The control of magnetic characteristics of BaM ferrite thin films by bias sputtering (abstract)

Abstract

The thin films of a magnetoplumbite type of barium (BaM) ferrite have been deposited on SiO2/Si substrates at a rate of 100 Å/min in a gas mixture of 10% O2–90% Ar at a pressure of 2 mTorr by using the facing targets sputtering (FTS) apparatus. They possessed excellent chemical stability and high corrosion resistivity as well as perpendicular anisotropy as large as applicable for perpendicular magnetic recording media. They also seem to be applicable for millimeter wave isolator and circulator. In this study, the saturation magnetization Ms, the coercive force Hc, and the anisotropy field Hk of BaM ferrite films have been controlled by adjusting the rf-bias voltages to substrate Vb during sputtering, where Vb was always negative. The dependencies of Ms and Hc on Vb were shown in Fig. 1. Ms took the maximum value as large as 345 emu/cc at Vb of −30 V and decreased as Vb decreased in the range below −50 V. On the other hand, the perpendicular Hc decreased as Vb increased in the range above −100 V and took the minimum value as low as 910 Oe at Vb of −95 V. Hk and the magnetic anisotropy constant Ku also greatly depended on Vb. Such an apparent Vb dependence of these magnetic characteristics of BaM ferrite films seem to be attributed to the definite change in c-axis orientation of hexagonal crystallite and the different distribution of Fe3+ ions among several occupation sites. These results indicated that the c-axis orientation of BaM ferrite crystallites were promoted by applying proper Vb. Consequently, the bias sputtering technique with FTS method may be useful for preparing the BaM ferrite films composed of the multilayers with different magnetic characteristics, even if only one pair of targets are used without adjusting the other sputtering conditions.