Effects of oxidation and abnormal grain growth on the magnetic properties of thin Fe-SiO2 granular films

In the Fe-SiO2 granular system the effects of oxidation and abnormal grain growth on the magnetic behavior are significant. As film thickness is reduc ed a larger fraction of Fe grains intersect the free surface and are prone to oxidation even in good vacuum conditions. Films coated with protective S iO2 layers were found to be unaffected by oxidation. The presence of a surf ace during annealing also affects the microstructural evolution. Transmissi on electron microscopy observations revealed a bimodal distribution of Fe g rain sizes in uncoated films due to grain merger assisted by surface diffus ion. This bimodal distribution of Fe grain sizes is associated with a coerc ivity (H-c) vs vol. % Fe curve containing two peaks. By contrast, SiO2 coat ed films exhibited a uniform microstructure without unusually large grains and a smoother H-c vs vol. % Fe curve with a well defined maximum. Room tem perature coercivities of similar to 1000 Oe can be routinely achieved in Fe -SiO2 granular films as thin as 10 nm. X-ray photoelectron spectroscopy stu dies showed evidence for the chemical interaction between Fe and SiO2 in Si O2/Fe/SiO2 trilayer model film samples. (C) 1999 American Institute of Phys ics. [S0021-8979(99)68908-3].