Perpendicular anisotropy of bias-sputtered GdCo film

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Abstract
Some important information about the structural change of GdCo sputtered film with substrate bias is obtained by using the replica technique. It is found that the increase in perpendicular magnetic anisotropy for increasing substrate bias is related directly with the ultrafine microstructure of the GdCo film. The relative substrate potential with respect to the Ar plasma depends either on Ar pressure during sputtering or on the external substrate bias. When this relative substrate potential becomes negative by a certain amount, sputtering of surface oxygen and resputtering of Gd in the growing film will be initiated, and consequently the structure of sputter-deposited film will change. The origin of microscopic perpendicular magnetic anistropy with or without substrate bias is described by a model proposed earlier for Permalloy films. The perpendicular magnetic anisotropy based on this microscopic shape anisotropy model is Ku = 2πMs2(δ/a), where δ is the thickness of the nonmagnetic boundary and ’’a’’ is the columnar diameter of the magnetic body. The quality factor Q is expressed as Q = (δ/a). These relations explain fairly well the increase in Ku with increasing negative bias voltage.