THERMAL-STABILITY OF ANISOTROPY IN TBFE FILMS PREPARED BY DC-MAGNETRON SPUTTERING

We have found that stresses induced during magnetron sputter deposition of amorphous TbFe films are very important in determining the thermal stability of the perpendicular anisotropy, K(u). To determine the stress-induced contribution to the anisotropy, the anisotropy was measured with a torque magnetometer before and after peeling films from their substrates. Data clearly show that the fractional change in anisotropy which occurs when the film is peeled from its substrate, DELTA-K(u)/K(u), decreases with increasing Ar pressures. Furthermore, annealing studies reveal that the thermal stability of K(u) improves with increasing Ar sputtering pressure-a trend which is in conflict with the tendency for films sputtered under low Ar pressure to be more oxidation resistant. This trend is attributed to the large stress-induced anisotropy component which exists at low argon pressures and its tendency to decrease as a result of long-term annealing. Measurements of the anisotropy of films which had been annealed at 200-degrees-C for 815 h showed that the residual K(u) after annealing increased with argon pressure. Measurements of the width of the peak in coercivity around T(comp) in these films shows that H(c) increases monotonically with argon pressure. This monotonic increase in H(c) is attributed to larger local variations in anisotropy caused by the less dense microstructure and the more random local anisotropy produced by the larger angle of incidence of adatoms which results from the increased scattering in the higher pressure sputtering gas.