MnAs 化合物 薄膜의 磁氣-光學的 效果 = Magneto-Optic Effect of MnAs Compound Thin Films

다국어 초록 (Multilingual Abstract)

For the ferromagnetic MnAs films of the NiAs crystal structure the magneto-optical properties were investigated.
MnAs thin films were prepared by vaccum cvaporation. As, Mn films were evaporated successivly onto glass substrates at room temperature. After being covered with siO layer, these layered films were annealed. The SiO layer was coated for the pirpose of enhancing the kerr rotation and obtaining a quality film free an oxidation during the annealing. The factors for the refined ferromagnetic thin films were examined by ajusting the conditions of evaporation process and thermal diffusion. To get the good ferromagnetic properties MnAs double-layered films must be annealed for more than 10 hours at temperature 300℃ in vacuum of 10^-5∼10^-6 Torr. The crystal structure of compound MnAs films was investigated by X-ray diffraction and was confirmed to be of NiAs type with the lattice constants a=3.70 Å and c=5.72 Å.
The magnetic hysteresis loops of Mn_(1+X)As (-0.2＜X＜0.2) films of the thickness 800 Å were measured by a mageto-potical method. The saturation magnetization (Ms) and the coercivity (Hc) are found to be varied with x and the maximum value of Ms, 630 Gauss and of Hc, 1900 Oe, are obtained with x=o. It is found that for the film of x＞o magnetization measurements are associated with the migration of excess mangnese ions into the bipyramidal interstices in which they are known to couple antiferromagnetically with the octahedral lattice site manganese ions.
The longitudinal magneto-optic Kerr effect is taken into account, for it is investigated that the film have the easy direction magnetization in the c-plane. The magneto-optic Kerr effect of the films was investigated by measuring the rotation angle of the polarization and the ellipticity of the reflected light from the film surface using an ellipsometer. The rotation angles were so small that a Faraday cell, which sinusoidally rotated the polarization of the reflected light, was employed to improve the experimental accuracy. The state of polarization was analytically represened by using as the refractive index, the index of absorption, the magneto-optic amplitude, its phase were obtained by analyzing the measured rotation angles and ellipticities in terms of the reflection coefficient derived by Voigt. The absorption coefficient, the figure of merit, reflectivity, specific Faraday rotation were also calulated using the above quantities.
Moreover the dependence of the optical indices upon the incident angle, the wavelength of the light (4500∼9500 Å), and the film composition have also investigated. For the film of x=o at an angle of incidence of 60˚ the dispersion of the Kerr rotation shows a change in sign at 7000 Å. A maximum Kerr rotation of +1.02×10 exp (-3) rad is found at 9000 Å and a maximum Kerr ellipticity of -2.6×10 exp (-3) rad at 7000 Å. The complex index of refraction increases from N=1.82-j 1.75 at 4500 Å to 2.11-j 3.30 at 9500 Å. Q_O and q increase from 8.0×10 exp (-3) and 30˚ at 4500 Å to a maximum of 19.2×10 exp (-3) and 55˚ at 9000 Å, respectively. From these data a specific Faraday rotation of 156000˚/㎝ and an absorption coefficient of 4.5×10 exp (5)/㎝ were calculated at 8000 Å. The figure of merit value of 0.34˚ is approximately 50 % of the value measured for MnBi films on glass in this wavelength region and is large enough to be useful as a material for magneto-optic read out devices of application in beam addressable memories. We show that the magneto-optic effect in MnAs is enough for MnAs to be considered as a magneto optic material.