Uniaxial Anisotropy Studies in Amorphous Tb-Fe on Polyimide Substrates

Abstract

Amorphous Tb-Fe films have been RF sputter deposited onto water cooled Kapton polyimide substrates at three different Ar pressures and at 80 W RF power. M-H and polar Kerr loops have been studied, Torque measurements have been made in the temperature range from 6 to 300 K. For Ar pressure of 8mTorr, a maximum uniaxial anisotropy K_u value of 2.4.10⁶ erg/cm³ has been found and is attributed, in part, to stress (compressive) effects. As T is decreased, K increases in contrast to films deposited onto glass substrates. This is explained in terms of the absence of stresses in the sample caused by cooling because the thermal expansion coefficients of the Kapton and the Tb-Fe film are comparable. On the contrary, for a glass substrate which has a low thermal expansion coefficient, additional tensile stresses are induced under such circumstances which lead to a decrease in the value of the stress anistropy term. Cooling in a magnetic field is shown to modify the torque curves.