Magnetic properties of epitaxial TmFe2O4 thin films with an anomalous interfacial structure†
TmFe2O4, a member of the RFe2O4 family (R = Sc, Y, In, and Dy to Lu), shows both charge and spin orderings and exhibits interesting dielectric and magnetic phenomena. We have grown epitaxial thin films of TmFe2O4 on (111)-oriented YSZ (yttria-stabilized zirconia) substrates via the pulsed laser deposition method and explored their interfacial structure at the atomic level and magnetic properties. The out-of-plane X-ray diffraction and reciprocal space mapping results reveal that the TmFe2O4 thin film grows with the c-axis perpendicular to the (111) surface of the YSZ substrate. The structure of the TmFe2O4/YSZ interface was investigated by using scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). Interestingly, the hexagonal TmFeO3−δ phase has been found at the interface between the TmFe2O4 thin film and the YSZ substrate with the Tm3+-rich region at the upper side of the substrate. We suggest the possible growth mechanism based on the structural analysis. TmFe2O4 itself exhibits a spin or cluster glass transition, as verified by the fact that the external magnetic field dependence of irreversible transition temperature is described well in terms of the de Almeida–Thouless line and that the aging-memory effect is clearly observed. Furthermore, the field-cooled hysteresis loops and training effect clearly demonstrate the presence of the intrinsic exchange bias at 100 K due to the unique magnetic structure of the interface.