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MAGNETO-OPTICAL PROPERTIES OF AMORPHOUS TbFe ALLOYS M. Mansuripur, M. Ruane, P. Wolniansky, S. Chase, R. Rosenvold Boston University, College of Engineering, 110 Cummington Street, Boston, MA 02215. ABSTRACT Hysteresis loops and anisotropy energy constants are measured in a magneto-optical system that combines Kerr rotation and ellipticity to enhance signal strength. Temperature dependence of the polar Kerr effect is compared with the magnetization of the iron subnetwork in the mean-field approximation and good agreement is obtained. Perpendicular magnetic anisotropy is studied by magneto-optical methods, yielding the first two coefficients of the series expansion of anisotropy energy in terms of the angle of deviation from the easy axis. 1.

INTRODUCTION

Amorphous rare earth-transition metal (RE-TM) alloys are now considered the most promising media for erasable optical data storage applications [13]. In this paper magneto-optical measurements on TbFe alloys, prepared by sputtering onto quartz substrates, are compared with theoretical models. Section 2 describes hysteresis loop measurements and compares temperature dependence of the magneto-optical Kerr effect and the iron subnetwork magnetization derived from a mean-field theory. Results of anistropy measurements are given in Section 3 where we show that second order terms must be included in the expression for uniaxial anisotropy energy. 2.

HYSTERESIS LOOP MEASUREMENTS

Magneto-optical measurements of hysteresis loops versus temperature were performed in a differential detection system using HeNe light at X = 633 nm. All samples were sputter-deposited.on quartz to a thickness of about 1000 A and in-situ overcoated with 300 A of Si0 2 . The laser was incident on each sample from the overcoated side while an axial electromagnet created a 0.1 Hz sinusoidal magnetic field of amplitude Hmax. The three samples described here (samples I, II and III) were analyzed by X-ray fluorescence and found to be Tb2 8 . 3 Fe 7 1 . 7 , Tb2 0 . 3 Fe 7 9. 7 and (Tb 1 7 Fe 8 3 )9 4 Cu6 , respectively. The magneto-optic effect at red or near infrared wavelengths is believed to be mainly the result of interaction between light and the transition metal subnetwork in RE-TM alloys. To a first order approximation, the Kerr rotation angle 8k is proportional to the magnetization of the TM subnetwork:

MFe(T) = POk(T)

(1)

where P is the proportionality constant. The iron subnetwork magnetization can be calculated from the mean-field theory [4]. Fig. 1 shows the mean-field results for (Tb2 gFe 7 1 ) 8 5 Arj 5 (solid lines). The points (x's) represent measured Ok(T) for sample I with P=2500. The hysteresis loops are square at all temperatures up to the Curie point and the behavior of Hc vs. temperature is characteristic of Tb-rich samples with no compensation point temperature.

Mat. Res. Soc. Symp. Proc. Vol. 58. '1986 Materials Research Society

182

Although the mean-field theory and measured values of Ok agree extremely well, a second independent test of the model considers data obtaine