SPIN-FLIP ANOMALIES IN EPITAXIAL ALPHA-FE2O3 FILMS BY MOSSBAUER-SPECTROSCOPY

The spin-flip transition of 1000 angstrom-thick alpha-Fe2O3 films was investigated by conversion electron Mossbauer spectroscopy from 2.5 to 673 K. The films were epitaxially formed on alpha-Al2O3 single-crysta lline substrates by a reactive vapor deposition method. Not only the t ransition temperature but also the spin axis were found to strongly de pend upon the film orientation, probably as a result of anisotropic la ttice strains caused by interactions with the substrate. For a (102)-o riented film the transition takes place at about 400 K, much higher th an the Morin transition temperature (260 K) of the free crystal, and t he spin axis lying within the (102) plane above 400 K changes almost n ormal to the plane at room temperature and below: the normal makes 57. 6-degrees with the spin axis of the free crystal. A (001)-oriented fil m, on the other hand, does not show any transition at least down to 2. 5 K.