Magnetic states at the surface of alpha-Fe2O3 thin films doped with Ti, Zn or Sn
Abstract
The spin states at the surface of epitaxial thin films of hematite, both undoped and doped with 1% Ti, Sn or Zn, respectively, were probed with x-ray magnetic linear dichroism (XMLD) spectroscopy. Morin transitions were observed for the undoped (TM~200 K) and Sn-doped (TM~300 K) cases, while Zn and Ti-doped samples were always in the high and low temperature phases, respectively. In contrast to what has been reported for bulk hematite doped with the tetravalent ions Sn4+ and Ti4+, for which TM dramatically decreases, these dopants substantially increase TM in thin films, far exceeding the bulk values. The normalized Fe LII-edge dichroism for T<TM does not strongly depend on doping or temperature, except for an apparent increase of the peak amplitudes for T<100 K. We observed magnetic field-induced inversions of the dichroism peaks. By applying a magnetic field of 6.5 T on the Ti-doped sample, a transition into the T>TM state was achieved. The temperature dependence of the critical field for the Sn-doped sample was characterized in detail. It was demonstrated the sample-to-sample variations of the Fe LIII-edge spectra were, for the most part, determined solely by the spin orientation state. Calculations of the polarization-depedent spectra based on a spin-multiplet model were in reasonable agreement with the experiment and showed a mixed excitation character of the peak structures.
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