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NMR and ESR: interplay between orbital and spin degrees of freedom in rare‐earth titanates

Trivalent rare‐earth titanates exhibit an interesting interplay between spin, orbital and lattice degrees of freedom. Their magnetic ground state is defined by subtle lattice distortions which can be easily manipulated through chemical substitution or external stain. We will be presenting our magnetic resonance study on single‐ crystalline samples of Y(La, Ca)TiO3 in a wide range of isovalent substitution (La) and hole doping (Ca). The aim of our investigation was to elucidate the commonly ignored paramagnetic regime by utilizing nuclear magnetic resonance (NMR) and electron spin resonance (ESR). Anomalous behaviours have been detected at temperatures well above the Curie temperature (TC) in the stoichiometric compound YTiO3. Furthermore, the nature of the orbital state within these compounds is still not well understood. In our experiments, ESR of the unpaired Ti electron shows broad resonance lines at all temperatures and substitution/doping levels. We find that short electronic spin‐lattice relaxation times cause this. By modeling the relaxation as an Orbach process we were able to extract a small energy gap, likely produced by Jahn‐Teller splitting of the two lower Ti t2g orbitals. The value of the gap closely follows TC which indicates that full orbital degeneracy lifting is associated with ferromagnetic order. NMR was conducted on a spin‐1/2 89Y nucleus. Our results demonstrate a clear discrepancy between the static and dynamic local magnetic susceptibilities, with deviations from Curie‐Weiss behavior far above TC.

NMR ; ESR ; rare-earth titanates ; magnetizm

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