JPS6221167B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel structure of a magnetic head, particularly for reading magnetic information recorded in a linear magnetic material having a small coercive force in the center and a large coercive force in the surrounding shell. Concerning a new structure of a magnetic head.

FIG. 1 shows the structure of a linear magnetic material applied to the present invention. This magnetic material wire is the central part (core) 1
The core has a small coercive force, and the shell is magnetically hard and has a large coercive force. Both the core and shell have magnetic anisotropy in the axial direction, and the core part has a nucleation magnetic field (H
_N ) and the domain wall displacement magnetic field (H _W ). The thickness of the wire can be reduced to 0.012 inch or less in diameter, and its manufacturing method is disclosed in Japanese Patent Application Laid-open No. 8956/1989.

When magnetic information is recorded in the core and shell as shown in A and B of FIG. 1, a closed magnetic field as shown by the dotted line in the figure is formed and a stable state is obtained.

Next, the characteristics when an external magnetic field is applied to the wire will be explained with reference to FIG. FIG. 2a shows a case where a weak external magnetic field E ₁ is applied in the same direction as the shell's magnetic field, and since the external magnetic field E ₁ is weak, the internal state of the wire does not change at all. When the external magnetic field becomes strong as shown by _E2 in FIG. 2b, the direction of the magnetic field in the core is reversed under the influence of the external magnetic field, and as a result of the reversal, an output voltage _v1 is generated in the external magnetic head. The external magnetic field is as shown in Figure 2c.
As shown in FIG. 2b, the inside of the wire is the same as in FIG. 2b even though it is made stronger. Next, when the external magnetic field is removed as shown in Figure 2d, the core's magnetic field returns to its original state again as shown in the figure due to the closed magnetic field created by the shell, and as the core's magnetic field is reversed, it is applied to the external magnetic head. An output voltage v ₂ is generated.

Here, the output voltages v ₁ and v ₂ are caused by the movement of the domain walls, and are not caused by the movement of the medium in conventional magnetic recording, so the output voltages are relatively high (for example, if the wire is 0.5 V with a length of 15 mm) (distance between the magnetic head and the magnetic head is 0.5 mm), and when the wire is applied to recording on a magnetic card, a feature is obtained that the recording on the magnetic card is not erased by an external magnetic field.

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic head for reading information recorded by a wire having the characteristics described above, and in particular, to provide a magnetic head capable of generating a high output voltage.
To achieve this object, the present invention is characterized in that a magnetic head for reading magnetic information recorded in a linear magnetic material having a small coercive force at the center and a large coercive force at the surrounding shell portion is provided. a first excitation means for applying relatively weak excitation to the linear magnetic material; a second excitation means for applying strong excitation to the linear magnetic material in a direction opposite to the excitation by the first excitation means; The magnetic head has a magnetic sensor disposed at a position where the strength of the magnetic field between the excitation means is approximately zero. This will be explained in detail below with reference to the drawings.

In Figure 2, we have explained the characteristics of the wire when an external magnetic field is applied in one direction. Next, Figure 3 and 3 show the characteristics of the wire when an external magnetic field in both directions and an asymmetrical external magnetic field is applied. This will be explained with reference to FIGS. 4 and 5.

Figure 3 shows the situation of the applied external magnetic field, a
When a strong external magnetic field as shown by H in the figure is applied to the wire W, the magnetic field of the core is reversed and points in the same direction as the magnetic field of the shell, as shown in the figure. Next, as shown in FIG. 3b, when a weak magnetic field h in the opposite direction to H is applied, the magnetic field in the core returns to its initial state as shown. Figure 3c shows the state shown in Figure 3a after the strong external magnetic field H is applied again from the state shown in Figure 3b.
The situation is the same as that of

Figure 4 shows the output voltage generated in the magnetic head near the wire when a weak magnetic field and a strong magnetic field are applied alternately as shown in Figure 3.The horizontal axis is time and the vertical axis is the voltage scale. be. In FIG. 4, curves a and b represent asymmetric external magnetic fields applied to the wire, and the spike pulse A in FIG.
As shown in the figure, a large output voltage (0.5 V or more) is obtained due to the movement of the domain wall of the core as the transition from b to c in the figure occurs. The spike pulse B in FIG. 4 is an output caused by the movement of the domain wall of the core as it transitions from a to b in FIG. 3, and a relatively small output voltage is obtained as shown in the figure. The characteristics in Figure 4 are h = -20 oersted, H = +150
The horizontal axis is 2 msec/scale, and the vertical axis is 0.1 volt/scale.

Figure 5 shows the results when a weak external magnetic field and a strong external magnetic field are applied alternately as shown in Figures 3 and 4.
A of the diagram shows the magnetic hysteresis loop of the wire.
The discontinuities shown in and B occur as a result of domain wall switching, and the resulting output pulse is due to the presence of these discontinuities. Discontinuity A corresponds to output pulse A in FIG. 4, and discontinuity B corresponds to output pulse B in FIG.

As is clear from the above explanation, when an asymmetric external magnetic field is applied alternately to the wire, a high output voltage can be obtained due to switching of the domain wall. Among these, the amplitude of the output pulse A is very high, 0.5 volt or more, so it is very promising to use this pulse A as a reproduction output for magnetic recording.

FIG. 6 shows an example of the configuration of a magnetic head according to the present invention.
A shows an elevation view, B shows a plan view, and C shows a side view.
As shown in the figure, the magnetic head is provided on a base 10, a first excitation means 11 and a second excitation means 12 arranged in parallel thereon, and at a position that internally divides the space between them by l ₁ :l _{2 .} It consists of a magnetic sensor. Each excitation means 11 and 12 is a permanent magnet in the embodiment, and the permanent magnets are arranged in opposite directions as shown in order to apply oppositely oriented magnetic fields to the wire. In the embodiment, the magnetic sensor 13 has a coil 13a wound around a U-shaped ferromagnetic material. Magnetic sensor 13
may be placed at a position where the combined magnetic field of magnets 11 and 12 is almost zero, but it is more preferable to place it at a position where a slight positive magnetic field exists (a magnetic field corresponding to g in Fig. 5). Deploy. Therefore l ₁
The relationship between and l ₂ is l ₁ > l ₂ .

In the magnetic head having the above structure, it is assumed that relative motion is provided between the wire W and the magnetic head, and the wire W moves in the direction of the arrow in the figure. The wire first passes over the weak magnet 11, and its internal state is as shown in FIG. 3b. As the wire W moves to the left, the magnetic field applied to the wire changes as shown in FIG. 4b and a, and a spike pulse A is generated approximately at the boundary thereof. The magnetic sensor 13 is placed at a position where the spike pulse A is generated like a wire. Since a closed magnetic circuit is formed by the U-shaped ferromagnetic material and the wire, the coil 13a has a high voltage corresponding to the spike pulse A. Output voltage is obtained.

It is assumed that the permanent magnet 11 can apply a magnetic field of -20 Oe and the permanent magnet 12 can apply a magnetic field of +100 to +150 Oe to the wire.

FIG. 7 shows another example of the configuration of the magnetic head according to the present invention, in which one permanent magnet is hollowed out and the magnetic sensor is inserted into it in order to locate the magnetic sensor near the magnetic neutral point.

FIG. 8 shows a magnetic card (such as a bank card) to which the present invention is applied, in which wires are embedded in parallel in the recording track T of a plastic card CD in accordance with recorded information. Bits where wires are present are treated as information 1, bits where wires are not present are treated as information 0, and by moving the card over the magnetic head shown in FIG. 6 or 7, an output voltage corresponding to the recorded information is obtained.

As explained in detail in the embodiments above, the magnetic head according to the present invention is characterized in that the output voltage is extremely high because the output is generated by switching the domain walls, and the electric circuit connected to the head can be simplified. Furthermore, since the magnetic field of the wire is not extinguished by an external magnetic field, it is possible to obtain a recording medium that eliminates the disadvantage of extinguishment of conventional magnetic cards.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a magnetic wire to which the present invention is applied, FIG. 2 is an explanatory diagram of the operation of the wire in FIG. 1, and FIG.
Figures 4 and 5 are explanatory diagrams of the behavior of the wire when an asymmetric magnetic field is applied to the wire, Figures 6 and 7 are examples of the structure of the magnetic head according to the present invention, and Figure 8 is an example of the structure of the magnetic head according to the present invention. This is an example of a magnetic card. 10; base; 11; first excitation means; 12; second
Excitation means, 13: magnetic sensor.

Claims (1)

[Claims] 1. In a magnetic head for reading magnetic information recorded in a linear magnetic material having a small coercive force at the center and a large coercive force at the surrounding shell, compared to the linear magnetic material. a first excitation means for applying weak excitation to the target;
a second excitation means for applying strong excitation to the linear magnetic material in a direction opposite to the excitation by the first excitation means; and a second excitation means arranged at a position where the strength of the magnetic fields of the first excitation means and the second excitation means are approximately zero. What is claimed is: 1. A magnetic head comprising: a magnetic sensor; 2 The first excitation means is a permanent magnet that provides a magnetic field of approximately 20 oersted, and the second excitation means is a permanent magnet that provides a magnetic field of approximately 100 oersted.
A magnetic head according to claim 1, which is a permanent magnet that provides a magnetic field of 150 oersted.