X-ray absorption and x-ray magnetic circular dichroism in bulk and thin films of ferrimagnetic GdTiO3

Abstract

Perovskite rare-earth titanates are prototypical Mott insulators in which Ti 3+ ions with 3d 1 electronic configuration exhibit ferromagnetic or antiferromagnetic spin order, depending on the rare-earth size. This peculiar magnetic behavior has, however, been barely studied with element-specific probes, either in bulk or in thin films. The recent finding of fingerprints of ferromagnetism in two-dimensional electron gases at oxide interfaces involving rare-earth titanates has produced a surge of the interest in these complex materials. Harnessing the interfacial magnetic states in these heterostructures calls for a better understanding of their insufficiently explored magnetic states in bulk and especially in thin film form. In this paper, we combine high-resolution transmission electron microscopy with x-ray absorption spectroscopy and x-ray magnetic circular dichroism (XMCD) to determine the structural, electronic, and magnetic structure of GdTiO 3 in bulk and thin film form. In both cases, we find that the sample surface is strongly overoxidized but a few nm below, Ti is mostly 3+ and shows a large XMCD. We provide evidence for the ferrimagnetic nature of GdTiO 3 with antialigned Gd and Ti sublattices and show that, just as in antiferromagnetic LaTiO 3 or ferromagnetic YTiO 3 , Ti carries no orbital moment.

Growth and characterization of large (Y,La)TiO$_3$ and (Y,Ca)TiO$_3$ single crystals

“…A comparison with reference Ti 4+ spectra obtained for a SrTiO 3 single crystal clearly indicates that the additional XAS intensity in samples T3 and T4 appears in the energy range associated with the Ti 4+ spectral peaks, indicative of an overoxidation in samples T3 and T4. Such a partial conversion of Ti 3+ to Ti 4+ has been reported in several other XAS works on the RTiO 3 class of materials 19,20,25 . In order to confirm the effect of such oxidation on the magnetic properties, we performed XMCD measurements at 6 K, deep in the ferromagnetic phase.…”

“…Whereas this overoxidation effect can result from both cation vacancies and oxygen interstitials, the latter has been shown to be energetically favored 14 . The overoxidation effect has been the subject of recent studies, particularly of films, and has been shown to significantly affect magnetic and electronic properties 19,20 .…”