Magnetic states at the surface of alpha-Fe2O3 thin films doped with Ti, Zn or Sn

TL;DR

This study investigates the surface magnetic states of epitaxial alpha-Fe2O3 thin films doped with Ti, Zn, or Sn using XMLD spectroscopy, revealing dopant-dependent changes in Morin transition temperatures and magnetic behavior.

Contribution

It demonstrates that doping hematite thin films with Ti, Zn, or Sn significantly alters their surface magnetic states and Morin transition temperatures, contrasting with bulk behavior.

Findings

Sn and Ti doping increase Morin transition temperature in thin films.

Magnetic field can induce phase transitions in doped thin films.

Sample-to-sample variations are mainly due to spin orientation differences.

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 (T_M~200 K) and Sn-doped (T_M~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 T_M dramatically decreases, these dopants substantially increase T_M in thin films, far exceeding the bulk values. The normalized Fe LII-edge dichroism for T<T_M 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>T_M 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.