We have systematically investigated exchange coupled films of sputter deposited Ni80Fe20/FeMn and FeMn/Ni80Fe20 and obtained films with high exchange bias and low coercive forces. The variation of film properties with deposition conditions as well as with the permalloy and FeMn thicknesses have also been studied. The results demonstrated a strong dependence of exchange bias effect (HUA) on the amount of γ-phase FeMn, the amount of impurities, as well as the abruptness of the transition profile at the interface. In addition, our results have also raised a number of new questions concerning the magnetic state of the interface and the origin of the interface coupling phenomena.

A mean-field model of the magnetic properties of amorphous rare-earth–iron alloys has been developed which incorporates an Fe spin whose dependence on both the concentration and the species of rare earth is based on Mössbauer spectra. Using this model with a single fixed set of exchange constants, we have been able to calculate Curie temperatures which are in reasonable agreement with the data for amorphous rare-earth (Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu–iron alloys containing between 50 and 100 at.% iron. Better agreement with the measured Curie temperatures is achieved if the magnitudes of the Fe-Fe and rare-earth–Fe exchange constants are allowed to increase linearly with rare-earth concentration. The latter case has the additional advantage of reproducing the observed shape of the magnetization-vs-temperature curves for wide range of composition and rare-earth species.

We have been able to prepare amorphous oxides of Fe and Cr by sputter deposition. Magnetization measurements were made between 4.2 K and 300 K. Mössbauer spectra were obtained for the iron oxide samples in the same temperature range. Amorphous CrO2 films showed no evidence of magnetic order. For the amorphous Fe oxide films, the 4.2 K Mössbauer spectrum showed a broad symmetric six line pattern which collapsed to a doublet at T?100 K. The susceptibility of amorphous iron oxide shows a broad maximum near T=100 K and a paramagnetic moment of only 3μβ. We present arguments that this behavior cannot be described by superparamagnetism and therefore represents the intrinsic magnetic behavior of amorphous iron oxide.

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