Magnetostrictive properties of amorphous and partially crystalline TbDyFe thin films

Abstract

A series of amorphous and partially crystalline giant magnetostrictive thin films of the composition (Tb0.3Dy0.7)39Fe61 has been prepared by dc magnetron sputtering. The sputtering conditions were the same for all samples apart from the substrate temperature TS, which varied between 330 and 510 °C. The crystalline state and the magnetic properties of the samples were investigated in relation to the substrate temperature. Films deposited at TS=330–400 °C were amorphous. Crystallization started at TS=425 °C. The magnetostrictive coefficient λ, at 4 kOe and at room temperature, increased with increasing TS from 185 to 750 ppm at Hmax. This was related also to an increase of the Curie temperature TC from 35 to 315 °C. The hysteresis loops of the amorphous samples showed coercivities lower than 10 Oe. These samples presented λ≈300 ppm in a field of 1000 Oe. The direction of the magnetic moments in the amorphous films changed gradually from perpendicular to parallel to the film plane with increasing TS. The samples deposited at TS⩾425 °C showed λmax≈350–750 ppm, but the magnetostrictive curve was much broader and shifted to the value of Hc.