Microstructure and stripe domains in Ni–S ferromagnetic thin films

Abstract

Stripe domains have been observed in Ni–S ferromagnetic thin films electrolytically deposited. There is a critical thickness of such films: a minimum thickness above which the stripe domains will be formed. The critical thickness is determined by the composition of these films. Ni–S films exhibit a stripe domain structure if they are 90–400nm in thickness and if the sulphur concentration is within the range of 8–20 at%. The presence of sulphur in these films leads to the appearance of this domain structure. Our experimental results concerning the behaviour of stripe domains in external magnetic field and referring to the variation of reduced remanence, coercive field, effective anisotropy constant suggest that stripe domains structure in Ni–S films may be caused by several mechanisms which together or alone can give rise to an ‘oblique’ anisotropy tilted out of the film plane. For the Ni–S films containing more than 8 at%, the coexistence of the crystalline and amorphous phases was observed. The presence of the amorphous phase could be due to internal stress increase. On the other hand, it is expected that the presence of sulphur in the Ni matrix creates the microstructural faults and intrinsic non-homogeneities during the deposition process which are ‘frozen’ in originating internal stress fields and so it gives rise to a magnetoelastic anisotropy. After the thermal treatment for 1h at 600K the coercive field of various thickness films is smaller than untreated films which demonstrates the existence of an internal stress diminishing.