JPS60243539A - Magnetooptic effect measuring device - Google Patents

Abstract

PURPOSE:To suppress the interference property of laser light and to measure magnetooptic effect highly accurately, by providing a magnetic thin film at the position of the focal point of a condenser lens. CONSTITUTION:Laser light 14, which is emitted from a laser light source 13, is reflected by a mirror 15 and inputted to a polarizer 16. The light passes a Faraday cell 17, is converged by a condenser lens 18 and reaches a sample to be measured 20. In the sample 20, a magnetooptic recording layer 22 is formed on a substrate 21. The sample 20 is placed at the plane of the focal point of the condenser lens 18. When the converged laser light 14 is inputted on the sample 20, part of the light is reflected by the surface of the substrate 21 of the sample 20 and becomes reflected light 23'. The rest of the converged laser light 14 is reflected by the interface between the substrate 21 and the recording layer 22 and becomes reflected light 23. The reflected light 23 is converted into parallel light by a lens 24 and inputted to a light detector 26. Meanwhile, the reflected light 23' from the surface of the substrate 21 is not inputted to the light detector 26. Therefore the two reflected light beams are not interfered, and the sample to be measured 20 can be accurately measured.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a magneto-optic effect measuring device used for measuring magneto-optic effects - Kerr effect, Noah 2-Day effect - of a recording medium used for magneto-optical recording. .

(Prior art and its problems) Optical recording, especially optical disk memory, has attracted attention in recent years as a type of large-capacity file memory that enables high-density, large-capacity recording, as well as non-contact and high-speed access. There is. Among them, MnB1. MnCu
B1. MnTiB1. Crystalline magnetic thin film such as Mn/JGe or Tb%Gd, Dy%n.

Magneto-optical disk memory uses a magneto-optical recording layer consisting of an amorphous magnetic thin film created by combining rare earth metals such as Fe, Co, and transition metals such as Fe, Co, Ni, etc. It is said that it is possible to rewrite recorded information. Because of its advantages, it is being actively researched in various places.

Conventionally, a magneto-optic effect measuring apparatus as shown in FIG. 1 has been used as a method for evaluating the characteristics of magneto-optical recording media. Light 2 emitted from a light source 1 is reflected by a mirror opening, converted into linearly polarized light in one direction by a polarizer 3, and after passing through a Faraday cell 4, enters a recording medium 6 placed in an electromagnet 5. The recording medium 5 usually has a magneto-optical recording layer 8 formed on a substrate 7 made of glass or plastic. Reflected light 9 from the recording medium 6 passes through an analyzer 10 and reaches a photodetector 11 . The light 2 incident on the recording medium 6 passes through the magneto-optical recording layer 8
The plane of polarization rotates due to the magneto-optic effect depending on the magnetization direction. Therefore, the plane of polarization of the reflected light 9 varies depending on the magnetization state of the magneto-optical recording layer 8, and the intensity of the reflected light 9 that has passed through the analyzer 10 changes depending on the magnetization state of the magneto-optical recording layer 8. As a result, if the output of the photodetector 11 is plotted on the vertical axis and the magnetic field applied to the recording medium is plotted on the horizontal axis, a hysteresis loop as shown in FIG. 2 is obtained. The vertical axis corresponds to the rotation of the plane of polarization caused by the magneto-optic effect of the recording medium 6. The rotation angle (can be calibrated using the Faraday cell 4 and can be determined from FIG. 2. Also, the coercive force of the recording medium 6 can be determined from the lateral width of the loop in FIG. 2. The quality of the recording medium 6 The rotation angle is an important factor in determining the rotation angle θ, and it is essential for a magneto-optic effect measuring device to accurately measure the rotation angle θ.

A monochromator and a lamp or laser are used as the light source 1 of the magneto-optic effect measuring device.

In magneto-optical recording, since the recording medium is used with incidence on the substrate side, the magneto-optic effect is mainly measured by making light incident on the recording medium 60 from the substrate side. When a laser is used as the light source 1, when the laser beam enters the recording medium 6 as a parallel beam from the substrate side, the reflected light from the substrate surface and the reflected light from the substrate-magneto-optical recording layer interface are detected by the photodetector. 11, which significantly reduces the magneto-optic effect, that is, the measurement accuracy of the rotation angle. Figure 3 shows the magneto-optical effect (Kerr rotation angle) of a TbFe film (1500^ thick) fabricated by sputtering on glass substrates (0.5 m thick) with different degrees of parallelism using a HeNe laser (wavelength 632
This is the result of measurement using parallel light (beam diameter 2WO) of 8A) with incidence on the substrate side. It can be seen that when a substrate with good parallelism is used, the variation in the Kerr rotation angle depending on the measurement location is large, and the interference of laser light extremely reduces the measurement accuracy.

One method of avoiding the coherence of the light source is to use a monochromator and a lamp as the light source 1.

However, in this case, since the amount of light reaching the photodetector 11 is extremely small, a photomultiplier (photomultiplier tube) that requires a high-voltage power supply is required as the photodetector 11, and the device configuration becomes complicated.

(Objective of the Invention) The object of the present invention is to eliminate such conventional drawbacks, use laser light as a light source, suppress the interference of the laser light,
An object of the present invention is to provide a magneto-optic effect measuring device that can measure magneto-optic effects with high precision.

(Structure of the Invention) According to the present invention, in a magneto-optic effect measurement device that uses a laser beam as a light source and measures the magneto-optic effect of a magnetic thin film using reflected light from a magnetic thin film having perpendicular magnetic anisotropy, A magneto-optical effect measuring device is obtained, characterized in that a lens is placed in front of the magnetic thin film, and the magnetic film is placed on the focal plane of the lens.

(Detailed Description of Configuration) The present invention solves the problems of the prior art by adopting the above-described configuration. By condensing the laser beam incident on the magnetic thin film with a condenser lens placed in the laser beam path, and placing the magnetic thin film at the focused position, the reflected light from the surface of the substrate supporting the magnetic thin film and the reflected light can be separated. , it is possible to completely separate the light reflected from the substrate and the magnetic thin film interface. Thereby, it is possible to cancel the interference effect caused by the reflected light on the photodetector of the magneto-optic effect measuring device, and it is possible to perform accurate measurement.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 4 is a configuration diagram of a magneto-optical effect measuring device to which the present invention is applied. Laser light 14 emitted from laser light source 13 is reflected by mirror 15 and enters polarizer 16 . Furthermore, the laser beam 14 is 7 Alade cell 17
The light is focused by the condensing lens 18, and the electromagnet 19
It reaches the magneto-optical recording medium 20 placed inside. The magneto-optical recording medium 20 has a magneto-optical recording layer 22 formed on a substrate 21, and the focal plane Km of the condenser lens 18 is set. The reflected light 23 from the magneto-optical recording medium 20 is returned to parallel light by the lens 24, and then the plane of polarization on the magneto-optical recording medium is determined by the analyzer 25, which is set to an almost extinction state with respect to the polarizer 16. The rotation is converted into a change in light intensity, which is incident on the photodetector 26.

Here, as the laser light source 13, a HeNe laser (
Wavelength 6328 large) and semiconductor laser (wavelength 8300A)
However, the laser light source is not limited to these two types, and various laser light sources such as Ar laser, He-Cd laser, and dye laser can be used. Although Durham-Thomson prisms were used as the polarizer 16 and the analyzer 25, other prisms may be used as long as they have good extinction ratios. The Faraday cell 17 is placed in an air-core coil, and the correspondence between the air-core coil current and the polarization plane rotation angle is calibrated in advance. As the condensing lens 18, a convex lens (focal length 20
0m) was used. The shape of the condenser lens 18 is not limited to this embodiment, but should be optimized depending on the design of the magneto-optic effect measurement device. The selection should be made so that the

As the magneto-optical recording medium 20, a TbPe film formed on a glass substrate with a thickness of 0.5 wow was used. As the lens 24, a lens having the same shape as the condenser lens 18 is used here. The lens 24 is used to return the reflected light 23 diverged from the magneto-optical recording medium 2° into parallel light, and the shape of the lens is not limited by this embodiment. As the photodetector 26, in this embodiment, a silicon photodetector with a light receiving area of 100 - is used.

FIG. 5 and FIG. 6 are diagrams showing the principle of the laser beam interference removal effect in the present invention.

FIG. 5 is a diagram showing the arrangement of a sample to be measured (magneto-optical recording medium) 6 and a parallel laser beam 2.9.9' photodetector 11 in a conventional magneto-optic effect measuring device using a parallel laser beam. It is. In FIG. 5, a part of the parallel laser beam 2 incident on the sample to be measured 6 is reflected by the surface of the substrate 7 of the sample to be measured 6, and becomes reflected light 9'. Next, the other parallel laser beam is reflected at the interface between the substrate 7 and the magneto-optical recording layer 8 of the sample to be measured, and becomes reflected light 9. Since the reflected light 9 and the reflected light 9' have the same reflection direction, the photodetector 11
The magneto-optical effect measurement accuracy of the sample 6 to be measured is degraded.

Next, FIG. 6 shows the condenser lens 18, laser beam 14, 23, sample to be measured (magneto-optical recording medium) 20, lens 24, and photodetector 26 of the magneto-optic effect measuring device to which the present invention is applied.
FIG. In Figure 6, laser beam 1
4 is first converted into convergent light by the condenser lens 18, and then enters the sample to be measured 20. A portion of the convergent laser beam is reflected by the surface of the substrate 21 of the sample to be measured 20, and becomes reflected light 23'.

Next, the other focused laser beam is reflected at the interface between the substrate 21 and the magneto-optical recording layer 22 of the sample to be measured, and becomes reflected light 23. The reflected light 23 is converted into parallel light by a lens 24 and guided to a photodetector 26 . Here, reflected light 23 from the substrate surface
Since the light beam ' does not enter the photodetector, there is strong interference between the two reflected lights, and the magneto-optical effect of the sample to be measured can be measured with high accuracy.

(Effects of the Invention) FIG. 7 is a diagram showing the measurement results of the magneto-optic effect (Kerr rotation angle) measured by the embodiment of the magneto-optic effect measuring device to which the present invention is applied. The measurement sample was a glass substrate (0
, 5 mm thick) by sputtering method.
It is a film (1500^ thick). HeNe v- as a light source
The measurement was performed from the glass substrate side using a laser (wavelength: 6328A). Although the samples were prepared on glass substrates with different degrees of parallelism, the Kerr rotation angle shows a nearly constant value regardless of the degree of parallelism of the substrates.

By using a laser beam focused by a condensing lens, interference effects caused by the measurement sample can be removed, making it possible to perform accurate measurements.

In addition, samples that can be measured by the magneto-optical effect measuring device to which the present invention is applied have various shapes, configurations, and compositions other than those with specifications shown in the examples of the present invention, and include plastic substrates in addition to reeds and glass substrates. It can be applied to measurements of samples created on substrates, samples with multilayer structures, other rare earth transition metal magnetic thin films, and crystalline magnetic thin films.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional magneto-optical effect measurement device, Fig. 2 is a diagram showing an example of a hysteresis loop obtained from a conventional magneto-optic effect measurement device, and Fig. 3 is a diagram showing an example of a hysteresis loop obtained by a conventional magneto-optic effect measurement device. A diagram showing an example of the measurement result of the obtained Kerr rotation angle, FIG. 4 is a configuration diagram showing an embodiment of the present invention,
5 and 6 are diagrams showing the principle of the laser beam interference removal effect according to the present invention, and FIG. 7 is a diagram showing an example of the measurement results of the Kerr rotation angle obtained according to an embodiment of the present invention. In the figure, 1... light source, 2, 14... output light, 3.16
...Polarizer, 4.17...Faraday cell, 5.1
9... Electromagnet, 6.20... Magneto-optical recording medium, 7.
21... Substrate, 8.22... Magneto-optical recording layer, 9.2
5...Analyzer, 11.26...Photodetector, 9.9'
, 23.23'... Reflected light, z2;'ts... Mirror, 13... Laser light source, 18... Condenser lens,
24...Lens. 71-1 Fig. 2 O 2 Fig. O 3 Fig. Substrate parallelism (1 m) 71-4 Fig. 75 Fig. O 6 Fig.

Claims (1)

[Claims] In a magneto-optical effect measuring device that uses a laser beam as a light source and measures the magneto-optic effect of the magnetic thin film using reflected light from a magnetic thin film having perpendicular magnetic anisotropy, a lens is placed in front of the magnetic thin film, A magneto-optical effect measuring device, characterized in that the magnetic thin film is placed on the focal plane of the X point.