The magnetic properties of Tb-Fe-(B) thin films fabricated by rf magnetron sputtering

The magnetic properties of giant magnetostrictive TbFe and TbFeB thin films are systematically investigated. The films were fabricated by rf magnetron sputtering using a composite target which consists of an Fe plate and Tb chips. The introduction of B to the films was done by using an Fe plate containing B. The microstructure, examined by X-ray diffraction, mainly consists of an amorphous phase and, at high Tb contents, a pure Tb phase also exists. A progressive change in the direction of anisotropy from the perpendicular to in-plane occurs as the Tb content increases from 35 to 68 at.% for the B-free TbFe films and from 44 to 67 at.% for the TbFeB thin films. The boundary at which the anisotropy change occurs shifts significantly towards to higher Tb contents when B is introduced to the films. The saturation magnetization exhibits a maximum at the Tb contents of 42 and 48 at.% and the values are about 5800 and 5100 G for the TbFe and TbFeB thin films, respectively. The coercive force, measured in the easy direction, decreases monotonically with the Tb content and ranges from 7.5 to 100 Oe when the films with in-plane anisotropy are considered. The magnetic softness of the present film which exhibits the coercive force of below 10 Oe and a typical squared-loop shape, and saturates at a low field of 1 kOe, is considered to be the best, to our knowledge, among this kind of thin films.