JP7616946B2 - Method for controlling magnetic nanowire devices - Google Patents

Description

The present invention relates to a method for controlling a magnetic nanowire device, and in particular to a method for controlling a magnetic nanowire device that records information as magnetic domains using a current magnetic field.

Conventionally, magnetic nanowires using materials with perpendicular magnetic anisotropy have been known. For example, it has been reported that magnetic domains have been successfully driven using a multilayer laminated film structure of cobalt (Co) and terbium (Tb), which have a proven track record as perpendicular magnetization films, and a multilayer laminated film structure of cobalt and palladium (Pd) as magnetic nanowire materials. In addition, a method has been considered in which a recording head for a conventional HDD is placed in contact with the magnetic nanowire as a recording element (recording section) in this type of magnetic nanowire device to record information. However, there are problems such as the recording head being unable to be placed closest to the magnetic nanowire because the protective film of the recording head is several hundred nanometers thick, and the recording head having mechanical operating parts such as a suspension, which causes misalignment during alignment.

To solve these problems, the magnetic nanowire device 101 shown in FIG. 15(a) is arranged so that the magnetic nanowire 110 and the conductor (recording element 120) are arranged in a position where they are twisted perpendicularly to each other, sandwiching the interlayer insulating layer 130. For ease of understanding, it is assumed that the magnetic nanowires 110 are all magnetized downward as an initial value.

Figure 15(b) shows the principle of forming magnetic domains in a magnetic nanowire device with this structure. By passing a current (recording current A) through the conductor (recording element 120), a current magnetic field (recording magnetic field H) is generated around the recording element 120 in a clockwise direction along the recording current A. When the strength of this current magnetic field becomes greater than the strength of the anisotropic magnetic field of the magnetic nanowire 110 with perpendicular magnetic anisotropy, an upward or downward magnetic domain can be formed (magnetic domain recording) on the magnetic nanowire 110. Figure 15(c) shows a schematic diagram of the spread of the recording magnetic field H in the cross section of the recording element 120 and the magnetic nanowire 110, and the state of the formed magnetic domain D. When the magnetic nanowire 110 is a perpendicular magnetization medium, the vector component in the film thickness direction of the recording magnetic field vector that spreads concentrically around the recording element 120 mainly contributes to magnetization reversal.

The evaluation system at this time is shown in FIG. 16 (a bird's-eye view of the device) and FIG. 17 (a cross-sectional view of the device). A recording power source 40 is connected to the recording element 120, and a recording current (pulse voltage) can be applied to the recording element 120. By changing the direction of the recording current (positive or negative current), it is possible to form upward and downward magnetic domains on the magnetic nanowire 110. Specifically, a terminal 40a of the recording power source 40 is connected to one end 121 of the conductor (recording element 120), and the other end 122 is grounded. A terminal 51a of a first driving power source 51 is connected to one end (left end) of the magnetic nanowire 110. A terminal 52a of a second driving power source 52 is connected to the other end (right end) of the magnetic nanowire 110. Reference numerals 40b, 51b, and 52b are ground terminals, and reference numerals 40c, 51c, and 52c are operation and display units.
When recording an upward magnetic domain, the recording power supply 40 applies a positive recording current (pulse voltage) to the recording element 120, and when recording a downward magnetic domain (pulse voltage), a negative recording current is applied. A first driving power supply 51 and a second driving power supply 52 are connected to both ends of the magnetic nanowire 110, and the magnetic domain on the magnetic nanowire 110 can be moved (driven) left and right. When moving (driving) the magnetic domain to the right, this is achieved by applying a driving current (pulse voltage) from the first driving power supply 51 to the second driving power supply 52. When moving (driving) the magnetic domain to the left, this is achieved by applying a driving current (pulse voltage) from the second driving power supply 52 to the first driving power supply 51.

Conventionally, a method has been widely used in which a conductor (metal wiring) arranged perpendicular to the magnetic nanowire is used as a recording element (see, for example, Non-Patent Document 1). In addition, in the recording magnetic field produced by a single recording element, the magnetic domains formed on the magnetic nanowire spread in the longitudinal direction of the magnetic nanowire, making it difficult to form minute magnetic domains, and their shapes also fluctuate. In response to this, a method has been proposed in which the conductor (recording element) has a U-shaped structure that crosses the magnetic nanowire twice, on the outward and return paths, and the combined magnetic field of the two conductors (recording elements) is used to record magnetic domains in the gap between the two conductors, thereby controlling the magnetic domain length (see Patent Document 1 and Non-Patent Document 2).

JP 2020-27805 A

Kondo, Takeshi, and seven others, "Controlling the position of magnetic domain walls in Co/Ni nanowires and its application to magnetic shift registers," Technical Report of the Institute of Electronics, Information and Communication Engineers, October 12, 2017, vol. 117, no. 24, pp. 13-16 Mayumi Kawana and 3 others, "Simulation of magnetic domain formation in magnetic nanowires with various recording element shapes," Abstracts of the Academic Lectures of the Magnetic Society of Japan, August 28, 2018, Vol. 42, p. 109

In the magnetic nanowire device 101, the recording element 120 and the magnetic nanowire 110 must be electrically isolated, so that the interlayer insulating layer 130 must be inserted between them. The interlayer insulating layer 130 must ensure insulation, but if it is made thicker than necessary, the distance between the magnetic nanowire 110 and the recording element 120 increases, weakening the current magnetic field applied to the magnetic nanowire 110. As a result, the recording current required for recording increases, and the application of a large current to the recording element 120 causes destruction of the element. For this reason, it is preferable that the interlayer insulating layer 30 is thin. However, by making the interlayer insulating layer 130 thin, there is a risk that part of the recording current will flow out as a leak current to the magnetic nanowire 110 during recording. This leak current will cause the magnetic domain already formed on the magnetic nanowire 110 to be unintentionally driven during magnetic domain recording. Since magnetic domain recording and magnetic domain driving occur simultaneously, there is a risk that the magnetic domain will expand during recording, increasing the minimum bit length.

Furthermore, in elements with large leakage currents, the magnetic domains to be recorded and those that have already been formed are destroyed by Joule heat (the magnetic domains become maze patterned), making magnetic domain recording itself difficult. Suppressing leakage currents is essential for stable magnetic domain recording. Because the film thickness of the interlayer insulating layer is very thin (for example, about 10 nm), when multiple magnetic nanowires are fabricated on the same substrate, differences in the individual variations can cause leakage currents.

In addition, in device manufacturing, when magnetic nanowires/interlayer insulating layer/recording element are formed on a substrate in that order, a layered structure is formed through many processes such as forming a pattern by electron beam lithography, depositing materials using a sputtering device, and removing resist. Therefore, even if a device is designed under conditions that would not generate leakage current, leakage current may occur due to yield issues during manufacturing (film thickness and uniformity of the interlayer insulating layer, edge shapes of the magnetic nanowires and recording element, non-uniformity of film thickness on the substrate, etc.). It is most desirable to manufacture an element that can completely suppress leakage current, but if unnecessary leakage current can be suppressed even in elements that generate leakage current by ingenuity of device control technology, the problem of element yield can be solved and even defective devices can be used to a certain extent.

The present invention was made in consideration of the above problems, and aims to provide a method for controlling a magnetic nanowire device that can suppress leakage current and achieve device operation.

In order to solve the above problem, the control method for a magnetic nanowire device of the present invention is a control method for a magnetic nanowire device including a magnetic nanowire which is a thin-line magnetic material, and a recording element which is arranged on the magnetic nanowire via an interlayer insulating layer and records information on the magnetic nanowire as magnetic domains by a current magnetic field, wherein the recording element has two conductor portions which intersect with the magnetic nanowire at a twisted position, the two conductor portions are connected, and during recording, a magnetic domain is recorded in a magnetic nanowire region on the magnetic nanowire which is sandwiched between the two conductor portions, and during recording, two or more recording power sources electrically connected to the recording element generate a predetermined potential difference between the recording power sources so that a recording current capable of recording the magnetic domain flows to the recording element and so that the potential difference between the magnetic nanowire and the recording element is reduced to a potential difference that suppresses the potential difference to a leak current of a current value that does not drive the magnetic domain on the magnetic nanowire, and pulse voltages of opposite signs are applied to the two conductor portions at the same timing from a pair of recording power sources connected to both ends of the entire connection of the two conductor portions.

The present invention provides the following excellent effects.
According to the method for controlling a magnetic nanowire device, it is possible to suppress the leakage current from the recording element to the magnetic nanowire in the magnetic nanowire device and realize the operation of the device. In addition, it is possible to increase the possibility that even a device that has a large leakage current and would not be used in the prior art can be utilized by suppressing the leakage current. Therefore, it is possible to improve the yield.

FIG. 2 is a schematic diagram showing a magnetic nanowire device according to an embodiment of the present invention connected to a power source. FIG. 1 is a schematic diagram of a magnetic nanowire device in which four magnetic nanowires used in the experiment are connected in parallel to a power source. 3 is a schematic diagram showing a cross section of the magnetic nanowire device in FIG. 2 and a power supply connection. 13 is a waveform diagram of a recording current flowing through a recording element when a pulse voltage is applied from a second recording power supply to the recording element in Experiment 1. FIG. 5 is a waveform diagram of leakage current 1 and leakage current 2 that flow to the magnetic nanowire when the recording current in FIG. 4 is passed through the recording element. FIG. 11 is a waveform diagram of a pulse voltage applied to a recording element from a first recording power source in Experiment 2. 13 is a waveform diagram of a pulse voltage applied to a recording element from a second recording power source simultaneously with a first recording power source in Experiment 2. FIG. FIG. 11 is a waveform diagram of a write current flowing through a write element in Experiment 2. 13 is a waveform diagram of leakage current 1 and leakage current 2 flowing through four magnetic nanowires in experiment 2. FIG. 11 is a timing chart of voltages applied when magnetic domain recording and magnetic domain driving are repeated in a magnetic nanowire device. 11 is a magneto-optical microscope image of magnetic domains generated in a magnetic nanowire device by repeating the timing chart of FIG. 10 . 11 is a schematic diagram of a first modified example of a method for controlling a magnetic nanowire device according to an embodiment of the present invention. FIG. 13 is a schematic diagram of a second modified example of the method for controlling a magnetic nanowire device according to the embodiment of the present invention. FIG. 13 is a schematic diagram of a third modified example of the method for controlling a magnetic nanowire device according to the embodiment of the present invention. FIG. FIG. 15(a) is a schematic diagram of a magnetic nanowire device, FIG. 15(b) is a schematic diagram (bird's-eye view) of magnetic domain recording on a magnetic nanowire, and FIG. 15(c) is a schematic diagram (cross-sectional view) of magnetic domain recording on a magnetic nanowire. FIG. 16 is a schematic diagram showing the magnetic nanowire device of FIG. 15 connected to a power source. 17 is a schematic diagram showing a cross section of the magnetic nanowire device in FIG. 16 and a power supply connection.

[Method for controlling a magnetic nanowire device]
A method for controlling a magnetic fine wire device will be described with reference to Fig. 1. In this embodiment, the magnetic fine wire device 1 will be described as a memory.
The magnetic nanowire device 1 includes a magnetic nanowire 10 which is a thin magnetic body, and a recording element 20 which is disposed on the magnetic nanowire 10 via an interlayer insulating layer 30 and records information as magnetic domains in the magnetic nanowire 10 by a current magnetic field. The recording element 20 has two conductor parts which intersect with the magnetic nanowire 10 at a twist position, and records magnetic domains in a magnetic nanowire region on the magnetic nanowire 10 sandwiched between the two conductor parts during recording.
The method of controlling the magnetic nanowire device is such that, during recording, two or more recording power sources electrically connected to the recording element 20 generate a predetermined potential difference between the recording power sources so that a recording current capable of recording a magnetic domain flows through the recording element 20 and so that the potential difference between the magnetic nanowire 10 and the recording element 20 is reduced, and pulse voltages of opposite signs are applied to the conductor portion from a pair of recording power sources 41, 42 connected to both ends of the conductor portion.

As shown in FIG. 1, the recording element 20 has a U-shaped structure with two connected conductor parts, and a pair of recording power sources 41, 42 are connected to both ends of the two connected conductor parts. In addition, two recording power sources (a first recording power source 41 and a second recording power source 42) are used here. It is preferable that the magnitude of the pulse voltage applied to the conductor parts from the pair of recording power sources 41, 42 is equal. During recording, it is preferable to reduce the potential difference between the magnetic fine wire 10 and the recording element 20 so that the current value of the current leaking from the recording element 20 to the magnetic fine wire 10 is reduced to a current value that does not drive the magnetic domain on the magnetic fine wire 10, and it is more preferable that the potential difference between the magnetic fine wire 10 and the recording element 20 is zero. Here, the magnetic domain on the magnetic fine wire 10 refers to the magnetic domain to be recorded on the magnetic fine wire 10 or the magnetic domain that has already been recorded.

[Configuration of magnetic nanowire device]
Next, the detailed configuration of each part of the magnetic nanowire device 1 will be further described.
1, the magnetic nanowire device 1 has, as an example, one magnetic nanowire 10 and a recording element 20 having two conductive wire portions. In the magnetic nanowire device 1, the recording element 20 is formed on the magnetic nanowire 10 via an interlayer insulating layer 30 at a twisted position relative to the magnetic nanowire 10.

The magnetic nanowire 10 is a thin film, and is formed in a narrow wire shape with a small thickness and width relative to its length. The thickness of the magnetic nanowire 10 can be, for example, 5 nm to 2 μm, the width can be, for example, 20 nm to 100 μm, and the length can be, for example, 100 nm to 500 μm. In the examples described below, the film thickness of the magnetic nanowire 10 is, for example, on the order of several nm. The magnetic nanowire 10 is formed into the above shape by electron beam drawing, photolithography, etching, or lift-off. In order to use the magnetic nanowire 10 as a recording medium and record information at high density, it is preferable to use a magnetic material with perpendicular magnetic anisotropy as the material for the magnetic nanowire 10. Such materials include alloys such as Co-Tb, Co-Pd, Co-Cr, Co-Pt, and Co-Cr-Pt, alloys of rare earth metals and transition metals such as Tb-Fe-Co and Gd-Fe (RE-TM alloys), and multilayer laminated structure films made of the above elements.

The recording element 20 is a conductor, and is a conductive layer for the recording element that forms a magnetic domain inside the magnetic nanowire 10 while being electrically isolated from the magnetic nanowire 10. The recording element 20 has a conductor portion arranged perpendicular to the magnetic nanowire 10 at a twisted position so as to straddle the magnetic nanowire 10 twice. The ranges of thickness, width, length, etc. of the recording element 20 can be roughly the same as the ranges of thickness, width, length, etc. of the magnetic nanowire 10. Note that in the embodiment described below, the film thickness of the recording element 20 is, for example, on the order of 100 nm.

As the material for the recording element 20, a general electrode material can be used. Specifically, for example, metals with good conductivity such as Cu, Al, Au, Ag, Ta, Cr, Co, etc., or alloys thereof can be mentioned. As a method for forming the recording element 20, for example, a film of the electrode material can be formed by a known method such as a sputtering method, and a process such as electron beam drawing or photolithography, and a process such as etching or lift-off can be used.

In the example shown in FIG. 1, the cross-sectional shape of the recording element 20 is circular, but it may be rectangular. The cross-sectional shape of the recording element 20 and the magnetic nanowire 10 may be square, rectangular, polygonal, circular, elliptical, etc.

The insulator forming the interlayer insulating layer 30 is made of a general insulating _material . Examples of such materials include oxide films such as _SiO2 and _Al2O3 , silicon _nitride ( _Si3N4 ), and MgF2. The shape of the interlayer insulating layer 30 is not limited to the flat plate shape shown in the figure as long as it is stably supported on a substrate (not shown), and for example, an insulating material may be filled between the recording elements _20. Alternatively, the interlayer insulating layer 30 may be an insulating coating in which an insulating material is spread around the recording elements 20.

[System Configuration]
As shown in Fig. 1, the evaluation system 2 that controls the magnetic fine wire device 1 includes a first recording power supply 41 and a second recording power supply 42, and a first driving power supply 51 and a second driving power supply 52. In the system 2, the same components as those in the system 102 shown in Fig. 16 are given the same reference numerals and will not be described. In the first recording power supply 41 and the second recording power supply 42, reference numerals 41a and 42a denote terminals, reference numerals 41b and 42b denote ground terminals, and reference numerals 41c and 42c denote operation display units. The first recording power supply 41 and the second recording power supply 42 are each connected to two terminals of the recording element 20, and are capable of applying pulse voltages of opposite signs to each other.
The first recording power source 41 and the second recording power source 42 are connected to both ends of a conductor (recording element 20) arranged in a U-shape.

During recording, a pulse voltage is applied to the recording element 20 from the first recording power supply 41, and a pulse voltage having the same amplitude and opposite sign to that of the first recording power supply 41 is applied from the second recording power supply 42 at the same timing. The recording current flowing through the recording element 20 at this time is the difference voltage between the pulse voltage from the first recording power supply 41 and the pulse voltage of the opposite sign from the second recording power supply 42, and a recording current according to the resistance value of the recording element 20 flows. At this time, the potential of the recording element 20 as seen from the magnetic nanowire 10 is the sum of the pulse voltage from the first recording power supply 41 and the pulse voltage of the opposite sign from the second recording power supply 42, so that it appears to be 0V, i.e., the same potential as the magnetic nanowire 10, and no leak current flows. In addition, the magnitude of the recording voltages of the first recording power supply 41 and the second recording power supply 42 do not necessarily have to be equal, as long as the potential difference is sufficient to pass a recording current and the potential difference of the recording element 20 as seen from the magnetic nanowire 10 is small enough to suppress leakage current, but it is most desirable that they are equal.

In this embodiment, the recording element 20 is U-shaped (a single conductor wiring crosses the magnetic nanowire 10 twice as it travels back and forth) as shown in FIG. 1, and is folded back at a portion other than directly above the magnetic nanowire 10. This configuration makes it easy to apply pulse voltages with the same amplitude but opposite signs to the first recording power source 41 and the second recording power source 42, and makes it possible to make the potential difference between the recording element 20 and the magnetic nanowire 10 appear to be 0 V.

[Magnetic nanowire device having multiple magnetic nanowires]
It is preferable that the magnetic nanowire device is configured to include a plurality of magnetic nanowires 10, and the two conductor parts of the recording element 20 cross the plurality of magnetic nanowires 10 at twisted positions. The reason is that when magnetic nanowire memories are realized in the future, it is expected that millions of magnetic nanowires will be arranged in parallel. It is also expected that the recording element will be arranged so that the two conductor parts are perpendicular to these parallel magnetic nanowires, and recording control will be performed in which magnetic domains having the same magnetization direction are recorded on all the parallel magnetic nanowires by a composite magnetic field generated in the gap between the two conductor parts.

Therefore, in the following, in order to verify whether the same information can be simultaneously recorded in multiple magnetic nanowires as shown in FIG. 2, basic experiments (Experiment 1, Experiment 2) will be described in which magnetic domain recording was attempted in a magnetic nanowire device in which four magnetic nanowires are arranged in parallel. In the system 2B shown in FIG. 2, the same components as those in the system 2 in FIG. 1 are given the same reference numerals and will not be described. The magnetic nanowire device 1B differs from the magnetic nanowire device 1 in FIG. 1 in that it has four magnetic nanowires 10. The recording element 20 has a U-shape, and two conductor parts cross each magnetic nanowire 10 twice at the twisted position, so that a magnetic domain is formed between the two conductor parts by the composite magnetic field of the current (recording current) flowing through the two conductor parts. By shortening the distance (gap) between the conductor parts, the range of the composite magnetic field can be narrowed, and the length of the recorded magnetic domain can be shortened. From the viewpoint of recording density, it is preferable to shorten the gap. For example, it is possible to form a fine gap of about 40 nm to 100 nm by using electron beam lithography. Below, we will explain Experiment 1 and Experiment 2 in order.

(Experiment 1)
Four magnetic nanowires 10 arranged in parallel are formed on a surface thermally oxidized silicon substrate by sputtering. The magnetic nanowires 10 used have perpendicular magnetization characteristics, and in this example, a multilayered film (4.5 nm thick) of cobalt and terbium is deposited with platinum thereon to give a total film thickness of 7.5 nm. The width of the magnetic nanowires 10 is 3 μm. The multilayered film is made up of five pairs of alternating layers of 0.3 nm thick cobalt and 0.6 nm thick terbium.

18 nm of silicon nitride was deposited on the magnetic nanowire 10 as the interlayer insulating layer 30. A U-shaped conductor (recording element 20) was formed on top of this with a thickness of 100 nm and a width of 3 μm. One side of the U-shaped conductor is the outgoing path, and the other is the return path, and magnetic domains are recorded in the gap of the recording element 20 by the combined magnetic field of the two conductors.

The gap between the conductor portions of the recording element 20 at this time was set to 100 nm. The thickness of the interlayer insulating layer 30 was set to 18 nm, which is a sufficient thickness to ensure insulation between the recording element 20 and the magnetic nanowire 10. However, an element with poor insulation caused by the yield in forming the multilayer device and non-uniformity due to the position on the substrate was selected. This element is assumed to generate a leakage current from the recording element 20 to the magnetic nanowire 10 when recording magnetic domains. The following experiment 1 was carried out using this element with poor insulation.

Experiment 1 is an experiment relating to a comparative example for explaining the effect of the present invention, and only the recording voltage application process is performed during magnetic domain recording. In experiment 1, a recording current was applied from the second recording power supply 42 without using the first recording power supply 41 in FIG. 2, and it was confirmed whether magnetic domain recording could be performed on each magnetic nanowire 10. From the experiments so far, it has been confirmed that in a state in which there is no leakage current, magnetic domain recording can be performed on the magnetic nanowire 10 when a current of about 100 mA flows through the recording element 20 in the magnetic nanowire 10 and the U-shaped recording element 20 of the above configuration. Furthermore, in the case of four magnetic nanowires 10 arranged in parallel as shown in FIG. 2, it has been confirmed from a prior experiment that magnetic domains are driven when a current of 15 mA flows through the entire four magnetic nanowires.

4 shows the waveform of the recording current when a recording current of 71.6 mA and 3 μs is applied to the recording element 20 from the second recording power supply 42 in the direction of the first recording power supply 41. The recording current can be observed, for example, by the second driving power supply 52. FIG. 5 shows leakage currents 1 and 2 that flow to the magnetic nanowire 10 through the interlayer insulating layer 30 at this time. Here, leakage current 1 is a leakage current that flows from the magnetic nanowire 10 to the first driving power supply 51 side as shown in FIG. 3, and leakage current 2 is a leakage current that flows from the magnetic nanowire 10 to the second driving power supply 52 side. The current values and voltage values described with reference to FIG. 4 to FIG. 8 are values at 1.5×10 ⁻⁶ s.

As shown in FIG. 5, the leakage current 1 was 13 mA, and the leakage current 2 was 15 mA. The magnitude of the leakage current 2 (15 mA) was the same as the driving current when driving the magnetic domains of the magnetic nanowire 10. Therefore, it was confirmed that the magnetic domains already formed on the magnetic nanowire 10 were driven to the right (toward the second driving power supply 52) in FIG. 3 by the leakage current 2. In addition, an attempt was made to apply a recording current of 100 mA from the second recording power supply 42, which would enable magnetic domain recording, but the leakage current became even larger, and not only did it drive the magnetic domains, but the magnetic domains of the entire magnetic nanowire became a maze pattern, making it impossible to record the magnetic domains. Note that the maze patterning of the magnetic domains is a phenomenon in which the magnetic domains of the magnetic nanowire are broken into pieces by Joule heat from the leakage current.

(Experiment 2)
Since the method of experiment 1 did not allow magnetic domain recording, two recording power sources 41 and 42 were connected to both ends of the conductor (recording element 20) as shown in FIG. 2. Then, the recording voltage (pulse voltage) shown in FIG. 6 was applied to the first recording power source 41, and the recording voltage (pulse voltage) shown in FIG. 7 was applied to the second recording power source 42 at the same time. Both of these recording voltages had an amplitude of 7.5 V and a pulse width of 3 μs, but the signs were opposite to each other. That is, the first recording power source 41 applied a recording voltage of −7.5 V to the recording element 20, and the second recording power source 42 applied a recording voltage of +7.5 V. Here, the pulse width was set to 3 μs, but it is not limited to this as long as it is a pulse width sufficient for magnetic domain recording. However, as a magnetic nanowire device, it is desirable to be able to record magnetic domains at high speed, and therefore a small pulse width is desirable, so that the pulse width is preferably about 20 ps to 5 μs, for example.

At this time, the potential difference between the second recording power supply 42 (positive pulse power supply) and the first recording power supply 41 (negative pulse power supply) is 15 V, and since a potential difference is generated, a current is applied to the recording element 20 in the direction from the second recording power supply 42 to the first recording power supply 41.
At this time, the potential difference between the magnetic nanowire 10 and the recording element 20 is the sum of the voltages of the first recording power supply 41 and the second recording power supply 42, and is therefore 0 V. This makes it possible to suppress leakage current from the recording element 20 through the interlayer insulating layer 30. In addition, the gap between the conductor parts of the recording element 20 is 100 nm, which is a sufficient distance compared to the film thickness (18 nm) of the interlayer insulating layer 30, and therefore no destruction of the element or destruction of the recorded magnetic domains due to leakage between the conductor parts was observed.

Figure 8 shows the waveform of the recording current (the direction from the second recording power supply 42 to the first recording power supply 41 is positive) that actually flowed through the recording element 20. Figure 9 shows the leakage currents 1 and 2 that flowed through the interlayer insulating layer 30 to the magnetic nanowire 10 at this time. As shown in Figure 8, a current of 108 mA (>100 mA) flows through the recording element 20, and it was confirmed that this recording current was sufficient to record magnetic domains in each magnetic nanowire 10. Also, as shown in Figure 9, the leakage currents 1 and 2 at this time were approximately -3 mA to +3 mA, which was suppressed to a value sufficiently lower than the driving current (15 mA) that drives the magnetic domains. Note that under the conditions of Experiment 2, a sufficiently suppressed leakage current that does not move the magnetic domains of the magnetic nanowire 10 is, for example, a current of 3.5 mA or less.

As an example, a case where upward magnetic domain recording and driving of the recorded magnetic domain at that time, and downward magnetic domain recording and driving of the recorded magnetic domain at that time are alternately repeated in the magnetic fine wire device 1 will be described with reference to FIG. 10. FIG. 10 is an example of a timing chart when magnetic domain recording and magnetic domain driving are alternately repeated in the magnetic fine wire device 1 using the first recording power supply 41, the second recording power supply 42, and the second driving power supply 52.

In this example, during magnetic domain recording, in the period from time t0 to time t11, in order to cause a recording current to flow from the second recording power supply 42 to the first recording power supply 41, a positive pulse voltage is applied to the recording element 20 from the second recording power supply 42 and a negative pulse voltage is applied from the first recording power supply 41.
Also, during recording of another magnetic domain, in the period from time t12 to time t13, in order to cause a recording current to flow from the first recording power supply 41 to the second recording power supply 42, a positive pulse voltage was applied to the recording element 20 from the first recording power supply 41 and a negative pulse voltage was applied from the second recording power supply 42.

During domain drive (time t11 to time t12, time t13 to time t14), the first drive power supply 51 was set to 0V, and the second drive power supply 52 was used as a negative pulse power supply, and a negative drive voltage (negative pulse voltage) was applied from the second drive power supply 52 to the magnetic nanowire 10 as shown in FIG. 10. For example, during the domain drive period from time t11 to time t12, a 500 ns pulse voltage was applied to the magnetic nanowire 10 three times, so that a drive current (14 mA, 500 ns drive current) flows from the first drive power supply 51 to the second drive power supply 52. In this method, even if there is a leak current from the recording element 20 to the magnetic nanowire 10, it can also be used as a drive current. Here, a 500 ns drive current is applied three times to perform a drive sufficient to observe the magnetic domain drive with a magneto-optical microscope, but the pulse width and the number of applications can be freely selected depending on the distance to which the magnetic domain is to be driven. However, increasing the pulse width can cause the magnetic nanowire to heat up, so this can be avoided by reducing the pulse width and increasing the number of times it is applied.

In addition, when driving the magnetic domain, the magnetic domain can be driven in the same manner by setting the second driving power supply 52 to 0 V and using the first driving power supply 51 as a positive pulse power supply to apply a positive driving voltage (positive pulse voltage) from the first driving power supply 51 to the magnetic nanowire 10.

Figure 11 is a magneto-optical microscope image of a magnetic nanowire in which upward and downward magnetic domains are alternately formed by repeating the timing chart of Figure 10, and shows an enlarged view of one of the four magnetic nanowires 10. In the magnetic nanowire 10, magnetic domains are recorded in the magnetic nanowire region between the center of one conductor part of the recording element 20 (left in Figure 11) and the center of the other conductor part (right in Figure 11). The four magnetic domains D are magnetic domains that are driven to the right from directly below the recording element 20. From the right end, they correspond to an upward magnetic domain, a downward magnetic domain, an upward magnetic domain, and a downward magnetic domain.

The present invention is not limited to the above-described embodiment, and various modifications are possible.
(First Modification)
Although the magnetic fine wire 10 includes Co-Tb as a magnetic material, other materials having perpendicular magnetic anisotropy may be used. If the magnetic material constituting the magnetic fine wire device includes a material that is oxidized by oxygen or moisture, such as Tb, the magnetic fine wire may be oxidized, which may make it difficult to drive the magnetic domain. If the magnetization in the magnetic fine wire is lost due to the progression of oxidation and the magnetic domain recording becomes difficult, the magnetic fine wire device will lose its function as a magnetic fine wire device. Therefore, depending on the type of magnetic material, it is preferable to seal the magnetic fine wire device in a container that can be sufficiently isolated from the outside air in order to prevent the magnetic fine wire device from being oxidized. A schematic diagram of this modified example is shown in FIG. 12. In the system 2C shown in FIG. 12, the same components as those in the system 2B shown in FIG. 3 are assigned the same reference numerals and will not be described. The container 60 that blocks the outside air isolates the magnetic fine wire device 1B from the atmosphere. Reference numerals 60a, 60b, 60c, and 60d denote connectors, which allow current to flow through the magnetic nanowire device 1B inside the container 60 while isolating it from the atmosphere outside the container 60. The atmosphere 70 inside the container 60, which blocks the outside air, is filled with a dry nitrogen atmosphere or is a vacuum. This modification prevents oxidation of the magnetic nanowire device, enabling more accurate control and evaluation of magnetic domain recording and magnetic domain driving.

(Second Modification)
The number of recording power sources used to control the magnetic fine wire device is not limited to two, and may be four as shown in FIG. 13. In the system 2D shown in FIG. 13, the same components as those in the system 2 shown in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted. In the third recording power source 43 and the fourth recording power source 44, reference numerals 43a and 44a are terminals, reference numerals 43b and 44b are ground terminals, and reference numerals 43c and 43c are operation display units. In the recording element of the magnetic fine wire device 1 shown in FIG. 13, the two conductor parts 20a and 20b are electrically separated. In this system 2D, four recording power sources 41 to 44 are used, and pulse voltages of opposite signs are applied to the conductor parts from a pair of recording power sources connected to both ends of the conductor parts so that recording currents flow simultaneously in opposite directions through the two conductor parts 20a and 20b of the recording element. Specifically, pulse voltages of mutually opposite signs are applied to the conductor portion 20a from a first recording power source 41 and a third recording power source 43 connected to both ends of the conductor portion 20a. At the same time, pulse voltages of mutually opposite signs are applied to the conductor portion 20b from a second recording power source 42 and a fourth recording power source 44 connected to both ends of the conductor portion 20b. This system 2D can achieve the same effects as the system 2 in FIG.

(Third Modification)
The number of recording power sources used to control the magnetic fine wire device may be three as shown in FIG. 14. In the system 2E shown in FIG. 14, the same components as those in the system 2 shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. In this system 2E, three recording power sources 41 to 43 are used to apply pulse voltages of opposite signs to the conductor portion from the first recording power source 41 and the second recording power source 42 connected to both ends of the conductor portion connected in the recording element 20. The third recording power source 43 can be connected to any position other than both ends of the conductor portion connected in the recording element 20. The recording voltage applied to the recording element 20 by the third recording power source 43 depends on the applied voltages of the first recording power source 41 and the second recording power source 42, and can be set according to the ratio of the length from the end of the recording element 20 to the third recording power source 43 to the total length of the conductor portion. This system 2E can also achieve the same effect as the system 2 in FIG. 1.

The magnetic nanowire device 1 is described as a memory, but it may also be a spatial light modulator. Furthermore, when used as a reflective spatial light modulator, it is preferable that the magnetic nanowire 10 is capable of changing the polarization state of the incident light, i.e., that it is strongly influenced by the magneto-optical effect.

1, 1B Magnetic nanowire device 2, 2B, 2C, 2D, 2E System 10 Magnetic nanowire (magnetic material)
20 Recording element 20a Conductor portion (recording element)
20b Conductive portion (recording element)
30 Interlayer insulating layer 41 First recording power source (recording power source)
42 Second recording power source (recording power source)
43 Third recording power source (recording power source)
44 Fourth recording power supply (recording power supply)
51 First driving power source 52 Second driving power source 60 Container for blocking outside air D Magnetic domain

Claims (9)

A method for controlling a magnetic nanowire device including a magnetic nanowire that is a thin-line shaped magnetic body, and a recording element that is disposed on the magnetic nanowire via an interlayer insulating layer and records information in the magnetic nanowire as a magnetic domain by a current magnetic field, the method comprising the steps of:
the recording element has two conductor parts that intersect with the magnetic nanowire at a twisted position, the two conductor parts are connected, and during recording, a magnetic domain is recorded in a magnetic nanowire region on the magnetic nanowire that is sandwiched between the two conductor parts,
A method for controlling a magnetic nanowire device, characterized in that during recording, two or more recording power sources electrically connected to the recording element generate a predetermined potential difference between the recording power sources so that a recording current capable of recording magnetic domains flows through the recording element and so that the potential difference between the magnetic nanowire and the recording element is reduced to a potential difference that suppresses the potential difference to a leakage current of a current value that does not drive the magnetic domains on the magnetic nanowire , and pulse voltages of opposite signs are applied to the two conductor portions at the same timing from a pair of recording power sources connected to both ends of the entire connection of the two conductor portions. the recording element has a U-shaped structure in which the two conductive wire portions are connected,
2. The method for controlling a magnetic nanowire device according to claim 1, wherein the pair of recording power sources are connected to both ends of an entire area where the two conductor portions are connected together. The method for controlling a magnetic nanowire device according to claim 2, characterized in that two recording power sources are used. The method for controlling a magnetic nanowire device according to claim 3, characterized in that the magnitudes of the pulse voltages applied to the conductor portions from the pair of recording power sources are equal. The method for controlling a magnetic nanowire device according to claim 3 or 4, characterized in that the potential difference between the magnetic nanowire and the recording element is reduced so that the current value of the current leaking from the recording element to the magnetic nanowire during recording is reduced to a current value that does not drive the magnetic domain to be recorded on the magnetic nanowire or the magnetic domain already recorded. A method for controlling a magnetic nanowire device including a magnetic nanowire that is a thin-line shaped magnetic body, and a recording element that is disposed on the magnetic nanowire via an interlayer insulating layer and records information in the magnetic nanowire as a magnetic domain by a current magnetic field, the method comprising the steps of:
the recording element has two conductor parts that intersect with the magnetic nanowire at a twisted position, the two conductor parts are electrically separated, and during recording, a magnetic domain is recorded in a magnetic nanowire region on the magnetic nanowire that is sandwiched between the two conductor parts,
A method for controlling a magnetic nanowire device , characterized in that, during recording, a predetermined potential difference is generated between four recording power sources electrically connected to the recording element so that a recording current capable of recording magnetic domains flows to the recording element and the potential difference between the magnetic nanowire and the recording element is reduced to a potential difference that suppresses the potential difference to a leakage current of a current value that does not drive the magnetic domains on the magnetic nanowire, and pulse voltages of opposite signs are applied to the conductor portions of each of the recording elements at the same timing from a pair of recording power sources connected to both ends of the conductor portion so that recording currents flow simultaneously in opposite directions to each other through the two conductor portions. the magnetic nanowire device includes a plurality of the magnetic nanowires;
7. The method for controlling a magnetic nanowire device according to claim 1, wherein the recording element is configured such that two of the conductor portions intersect with a plurality of the magnetic nanowires at a twisted position. The method for controlling a magnetic nanowire device according to any one of claims 1 to 7, characterized in that the magnetic nanowire device is a memory or a spatial light modulator. The method for controlling a magnetic nanowire device according to claim 8, characterized in that the magnetic nanowire device is sealed in a container that can be isolated from the outside air and kept in a dry nitrogen atmosphere or vacuum.

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