A NEW METHOD TO MEASURE THE PERPENDICULAR ANISOTROPY OF RE-TM AMORPHOUS FILMS USING SPONTANEOUS HALL EFFECT

Abstract

A new method to measure the effective magnetic anisotropy field (H:) of amorphous RETM films with perpendicular magnetic anisotropy is described. In this method, H; is determined by the measurement of spontaneous Hall effect. The experimental data for TbFe sputtered films agreed with the theoretical prediction. RETM amorphous films with perpendicular magnetic anisotropy, such as GdCo, GdFe, TbFe, GdTbFeCo, etc., have now attracted special interest because of their promissing possibility as magnetooptical recording material, and intensive studies have been concentrating on these materials. However, it has not yet been clearly explained why these amorphous films have the perpendicular anisotropy. By the way, it is not so easy to investigate the magnetic anisotropy of such RETM films by conventional torque method. The reasons are: 1) they are ferrimagnetic thin films and have compensation temperature, T,,,,, in the vicinity of room temperature, so that the value of saturation magnetization M, is very small, on the other hand, 2) the magnetic anisotropy field Hk is very large. Okarnoto, the first author of this paper, has recently developed a new method to measure the effective mag/ netic anisotropy field Hk = Hk-4rM, using the spontaneous Hall effect, which is very large in RETM films independent of their M, values [I]. According to his method, if the film has a rectangular Hall hysteresis loop (VH H loop) with magnetic remanence Hall voltage VH= this means the film has a rectangular M H / loop with remanence Mr then Hk can be determined from the VHr HII curve. Where, HII is the magnetic field applied in the direction of film plane. And if the film has a linear type of VH H loop as shown in figure 1, in which VH,? 0 due to the linear magnetization characteristics of the film, H; is determined from the Hall loop for the obliquely applied magnetic field in the direction a = 45' as illustrated in figure 2. In figure 1, a predicted Hall loop for a = 45' is also shown. In this paper, we deal with the latter case more detailed. Let us consider the case of figure 2, where the film has become a single domain state due to the sufficiently large applied field H. We define the effective uniaxial magnetic anisotropy energy K as 1 K = K, 2 a ~ : = -M,Hk. 2 (1) a= 4 5 O V H S / D --4 ---