Antiferromagnetic Domain Contrast in LaFeO3 Thin Films: Examined with X-ray Magnetic Linear Dichroism and Photo Electron Emission Microscopy

Abstract

This study will focus on strain induced by thermal history and thickness on antiferromagnetic epitaxial LaFeO3(110) thin films grown on Nb:SrTiO3(001) substrates. Lattice mismatching between film and substrate induce strain in the film lattice during growth of the film. This strain can be relaxed by thermal treatment after growth and may show tendencies in the domain size, shape and distribution related to strain. Thin films are grown in different thicknesses by rf magnetron sputtering and selected films are relaxed by thermal anneal treatment. The samples are investigated in room temperature and in heating experiments to obtain images of antiferromagnetic domain contrast along the L2 and L3 absorbtion egde of Fe by XMLD spectromicroscopy. Size of domains areas and contrast level are measured and related to the strain in the thin films. Averaged spectra of L2 absorbtion edge antiferromagnetic contrast showed a clearly observable domain contrast with consistently shaped energy spectrums. No difference in antiferromagnetic contrast due to lattice strain caused by lattice mismatching was observed. All as-grown samples showed comparable size, distribution and shape of antiferromagnetic domains on both polished and etched substrates. Relaxation of prepared samples in 1000±C for 12 hours in a 1 atm atmosphere of oxygen gave a distinct increase in size for the domains. Area calculation show a increase from typically 0.2 ¹m2 for as-grown films to 2 ¹m2 for relaxed films. Heating experiments estimate a Néel temperature of 625oK for as-grown films and 740oK for relaxed samples. The thermal anneal thus has a significant effect on LaFeO3 thin films as the domains increase in size and the Néel temperature in which the film is no longer antiferromagnetic increases to the Neel temperature of bulk LaFeO3. This preparation approach may be useful for further investigations of the exchange-bias effect.