Stability phenomena in amorphous rare earth-transition metal films

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Abstract
TbFe films have been prepared with a range of compositions near to the room temperature compensation point and subjected to annealing at 100°C for up to 800 hours. Measurements of magnetic properties as a function of anneal time revealed a decrease in coercivity coupled with an increase in saturation magnetisation for all compositions. Changes in M s appeared to conform to a Johnson-Mehl-Avrami. exponent of approximately 0.5. Rutherford back-scattering spectrometry and electron microscopy revealed that the most likely cause of the observed changes in magnetic properties was oxygen diffusion resulting in the formation of TbO n oxides in turn leading to local diffusion, segregation and crystallisation of b.c.c, α-iron. The addition of an aluminium protective overlayer stablised the films against these changes, at least for the time and temperature ranges studied.