JPS6059643B2 - magneto-optical converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is characterized in that when a material is irradiated with polarized light, for example, left-right circularly polarized light, the light excites magnetic ions in the material, and the direction and strength of the magnetization produced at that time is This invention relates to a magneto-optical conversion device for controlling

Traditionally, magnetic recording has been done in two ways: by winding a coil around a magnetic material such as a ferrite head and passing a recording current through the coil, and by irradiating it with laser light and changing the magnetization using the heat generated. However, such conventional recording methods have the disadvantage that high speed and high density are difficult to achieve due to factors determined by the quality of the material.

An object of the present invention is to provide a magneto-optical conversion device which eliminates the above-mentioned conventional drawbacks, has a much faster response speed than the conventional method, and is suitable for high-speed, high-density magnetic recording.

That is, the magneto-optical conversion device of the present invention excites magnetic ions in a substance with light and uses the magnetization generated at that time, and generates an ellipse of light having a wavelength corresponding to the energy of magnetization generated in the photo-induced magnetization storage. By irradiating the optically induced magnetized material with light whose ellipticity is changed in relation to the modulating signal and whose ellipticity is changed, the direction and strength of magnetization in the optically induced magnetized material is changed in relation to the modulating signal. It is characterized in that it is made to change according to

Hereinafter, the present invention will be explained in detail with reference to embodiments with reference to the drawings.

Examples of various configurations of magnetic recording devices applying the optically induced magnetization phenomenon are shown in FIGS. 1a to 1c.

In the configuration example of the optical communication signal receiver shown in FIG. Al.

When a single crystal of O3:Cr) is excited, when the light is circularly polarized to the right or left, the photo-induced magnetization Mz becomes -Mz in the opposite direction or +■ magnetization in the same direction with respect to the direction of travel of the light, respectively. arise. This change in magnetization is detected by the pickup coil 4 and taken out as an output signal from the signal receiver 2 via an amplifier 5 and a demodulator 6. On the other hand, in the perpendicular writing and normal writing configurations of the magneto-optical write head shown in FIGS. 1b and 1c, respectively, the modulated signal from the modulator 1 is When the crystal 7 is excited by light, the light-induced magnetization Mz changes in accordance with the change in the ellipticity of the light due to modulation.

The lines of magnetic force generated at this time can magnetize the magnetic tape 9 moving in the direction shown, as shown by the arrow.
The principle of operation is the same regardless of the difference in the writing mode shown in FIGS. 1B and 1C. The magneto-optical conversion device of the present invention utilizes the fact that the direction and intensity of induced deterioration can be controlled by changing the ellipticity of the excitation light. The following is a detailed explanation of the case.

Ruby's ground energy level, i.e., ground level 4A,
The selection rule and transition probability when excited by light between
As shown in the table, it is well known both theoretically and experimentally.
If we represent what is shown in Table 1 in a diagram, it becomes as shown in Figure 2 a, and the distance between the ground level ``A2'' and the excited level i (2E) is 6943A as shown in the figure. .
At the base level 4A2, in the zero magnetic field, MS = Shimon and MS = ±? It is divided into two levels. On the other hand, the excited quasi-position (2E) is degenerate to M″s=±↓.As is clear from Table 1 and Figure 2,
When a ruby is excited with light of wavelength 6943A that is tuned between the base level 4A2 and the excitation level 100 (2E), the right circularly polarized light (σ+) becomes (Ms=+艮→M″s=+ν
), (MS+M″s=-Q), and left-handed circularly polarized light (σ-
), the following transitions occur (MS=+M″s=+(MS=+M″s=10 questions)), and their transition probabilities are
(MS=±?→M″s=±closed): MS=shikose→M″s=
The ratio is 3:2.

Here, the right-handed circularly polarized light (σ+) is taken in the direction of rotation when the right-handed screw is tightened, and Ms. ．． The + sign of M″S is taken to be the traveling direction of the light (+Z). Next, Figure 2b shows the mode of transition when excited by right-handed circularly polarized light, and MS=? and MS = - closed and excited at a ratio of 3:2 at the same time), magnetization in the +Z direction decreases and apparent magnetization appears to occur in the -Z direction.

Similarly, when excited by left-handed circularly polarized light, magnetization occurs in the +Z direction, and when excited by linearly polarized light, magnetization in the +Z direction is simultaneously induced, and they cancel each other out, so that no magnetization appears on the outside. do not have.

Next, the results of measuring the photo-induced magnetization as described above are used in the third
As shown in the figure.

The measurement results shown in Figure 3 are obtained using a ruby laser as excitation light.
When a ruby single crystal is excited with the C axis of the crystal parallel to the traveling direction of light, the magnetization in the C axis direction is 10
Detected by the pickup coil of the turn, and 10
This is a measurement photo amplified by @. In the measurement photograph shown in Figure 3, Δ■Zσ1 indicates the signal voltage when excited by left-handed circularly polarized light, and Δ■zσ+ indicates the signal voltage when excited by right-handed circularly polarized light, and the lower (σ−, σ+) show the waveforms of the excitation laser beams, respectively. As shown in FIG. 2, the polarity of the signal voltage is reversed between right and left circularly polarized excitation. Next, FIG. 4 shows how the signal voltage changes when the difference between the right and left circularly polarized intensities of the excitation light is changed.

According to the characteristic curve shown in Figure 4, when circularly polarized light is formed by a linear polarizer and a wavelength plate, the difference in intensity between right and left circularly polarized light is
It can be seen that it changes with a period of . In other words, the strength of photo-induced magnetization is proportional to the difference in intensity between right-handed and left-handed circularly polarized light, and when excited by right-handed or left-handed circularly polarized light, it shows the maximum or minimum value, respectively, and when excited by linearly polarized light, it shows the maximum or minimum value, respectively. Sometimes the strength of magnetization is zero. These experimental results show that the strength and direction of magnetization can be controlled by changing the ellipticity of the excitation light. Note that the direction of optically induced magnetization of a ruby single crystal due to circularly polarized light excitation is determined by right circularly polarized light (
σ+) excitation, left circularly polarized (σ−) excitation and linearly polarized (σ
For ±) excitation, the experimental results shown in FIGS. 5A, b, and c, respectively, have been obtained, and are in good agreement with the theoretical predictions described above with respect to FIG. Next, Fig. 6 shows the experimental results of measuring the dependence of the signal voltage obtained as described above on the laser power.The characteristic curve shown in Fig. 6 shows that the signal voltage is proportional to the laser power. I understand. The time change in photo-induced magnetization caused by the transition between levels described above can be explained by assuming the following equation. Here, ■(σ±)(
t) is the time change when excited by linearly polarized light σ, and Ms. ．． ms'' is the magnetic moment in the substrate state and excited state, β indicates the Bohr magneton, and Nms-
? Ms″(t) indicates the time change of chromium (Cr) ions in ruby when transitioning from the ground state to the excited state, and furthermore, Gg=1.98, Ge=
2.45, and τ8 and τ8 indicate the relaxation times in the ground state and excited state, respectively, and τ8) γ8
There is a relationship between

In addition, N. ．． s−+Ms″(t) is obtained by using a laser waveform and a value determined by a power meter, and setting the reflectance at the end face of the ruby single crystal to 8%.

Next, if we plot the experimental results of photo-induced magnetization and the results calculated using equation (1) above, matching their respective peak values, we get a graph as shown in Figure 7. The results of the experiment described above can be well explained from the correspondence with the calculation results.

That is, as can be seen from FIG. 7, it is clear that the photo-induced magnetization depends on the intensity of the laser beam and there is no delay.
That is, the photo-induced magnetization changes closely following changes in light. On the other hand, in the magneto-optical conversion device of the present invention, a single crystal of a photo-induced magnetized material, such as ruby (Al2O3:Cr), which is magnetized by changing its energy level transition state depending on the polarization state of the irradiated light, is used. By adding a small amount of a magnetic element such as chromium (Cr) to the single crystal to replace the constituent element, the single crystal is irradiated with polarized light of a wavelength matching the replaced magnetic element to change its magnetized state. As can be seen from equation (1) above, the peak value of the intensity of photo-induced magnetization depends on the number of excited chromium ions, N. 9-. 5″(t).

However, as the number of excited chromium ions increases, the relaxation time in the ruby single crystal becomes shorter, so although the peak value of the photo-induced magnetization intensity increases, its decay becomes faster, and the average intensity That is, the strength in the low frequency range decreases. Therefore, when the concentration of chromium (Cr) in ruby increases, the peak value of the intensity of photo-induced magnetization increases and the relaxation time shortens, resulting in an increase in the high-frequency component of the photo-induced magnetization signal and a decrease in the magnetization signal. Broadband can be achieved. As is clear from the above, this phenomenon of photo-induced magnetization changing depending on the polarization state of the irradiated light does not occur only in ruby single crystals, but generally has the following properties. The same thing occurs in substances that have. In other words, as is clear from experiments using ruby and the results of their analysis, photo-induced magnetization occurs when the energy state of an ion transitions from one state to another, as shown in equation (1). , this occurs when the vector composition of magnetic moments associated with the transition is no longer zero. Therefore, regarding the generation of magnetic moments associated with optical excitation, materials that exhibit the following energy level state, such as vanadium V, A substance other than ruby can be used as a material for magneto-optical conversion.

That is, (1) the magnetic moment between the ground states changes.

(2) The magnetic moment between excited states changes.

(3) The magnetic moment between the ground states and between the excited states does not change, but the magnetic moment changes between the ground state and the excited state.

Next, the characteristic curve shown in Figure 7 is 67 millijoules (M
J) represents the time change in photo-induced magnetization when a ruby single crystal is excited with the laser power, and if the power of the laser light absorbed in the ruby single crystal is Jabs, then the value of the Ja ratio is Approximately 0.7 millijoules (MJ)
Therefore, the maximum value of photo-induced magnetization is 0.25 emuIy. J
a? That's about it.

Furthermore, the characteristic curve shown in FIG. 7 shows that the relaxation time can also be changed by an external magnetic field. The experimental results described above were obtained when the concentration of chromium (Cr) added to ruby (Al2O3) was 0.
It was measured on a sample with 026at%,
The relaxation time in zero magnetic field was 180 r1s.

However, for a sample with a chromium concentration higher than 0.026 at%, for example, 0.3 at%, the relaxation time in a zero magnetic field is about 100 r1S, and the photoinduced magnetization signal increases. In the above explanation, an example was described in which a trace amount of chromium (Cr) was added to a ruby single crystal to shorten its relaxation time.
Chromium (Cr) is not the only substance that can be added to ruby (Al2O3) to shorten the relaxation time; titanium (Ti) or trivalent vanadium (V3+) can also be added to shorten the relaxation time. ) by adding a trace amount of at least one of these different elements to
The speed of magneto-optical recording in the apparatus of the present invention can be further increased.

As is clear from the above explanation, since the present invention uses the magnetic moment of magnetic ions excited by optical energy, if the magneto-optical converter of the present invention is applied to magnetic recording, the speed of magnetic recording will be significantly increased. can do. In addition, since the laser beam can be focused extremely narrowly, high-density magnetic recording can be performed, and therefore, magnetic recording devices can be miniaturized. can get. Further, when a paramagnetic substance such as ruby is used, a hysteresis phenomenon does not occur, so that magneto-optical conversion with good linearity can be performed. Furthermore, magnetic tape, magnetic sheet,
If a magnetic material suitable for forming a magnetic recording medium such as a magnetic disk or a magnetic drum is used and exhibits the photo-induced magnetization phenomenon described above, the magnetic recording medium described above can be constructed using that material. This enables magneto-optical recording that does not require a magnetic head.

[Brief explanation of the drawing]

Figures 1A, b, and c are configuration diagrams each showing an example of the configuration of a device that applies the photo-induced magnetization phenomenon, Figures 2A and b are diagrams schematically showing the mode of photo-induced magnetization generation, and Figure 3 The figure is a characteristic curve diagram showing an example of measurement results of photo-induced magnetization, Figure 4 is a characteristic curve diagram showing an example of ellipticity dependence of photo-induced magnetization, and Figure 5A
, b, c are diagrams showing the relationship between the state of polarized light and the direction of optically induced magnetization, respectively; FIG. 6 is a characteristic curve diagram showing an example of the dependence of the optically induced magnetization signal on the excitation light power; Figure 7 is a characteristic curve diagram showing an example of the correspondence between experimental results and theoretical calculation results regarding optically induced magnetization. 1... Modulator, 2... Signal receiver, 3
...Photo-induced magnetized material (ruby single crystal), 4...
... ZETSUKUUP COIL, 5 ... Amplifier, 6
... Demodulator, 7... Photoinduced magnetization crystal, 8.
...Yoke, 9...Magnetic tape.

Claims (1)

[Scope of Claims] 1. The ellipticity of light having a wavelength corresponding to the energy of magnetization generation in the photo-induced magnetization storage device is changed in relation to a modulation signal, and the light with the changed ellipticity is used to generate the photo-induced magnetization storage device. 1. A magneto-optical transducer characterized in that the direction and strength of magnetization in the photo-induced magnetized substance are changed in relation to the modulation signal by irradiating the photo-induced magnetized substance. 2. The method according to claim 1, characterized in that the relaxation time of the photo-induced magnetized material is shortened by adding an element different from the element constituting the magnetized material to the photo-induced magnetized material. Magneto-optical conversion device. 3. The magneto-optical device according to claim 2, wherein the photo-induced magnetization storage is made of Al_2O_3, and at least one element among Cr, Ti, and trivalent V is added to the Al_2O_3. conversion device. 4. The magneto-optical conversion device according to claim 2, wherein the photo-induced magnetization storage is made of Al_2O_3, and more than 0.3 at% of Cr is added to the Al_2O_3.