Abstract
The atomic environments involved in the magnetostriction effect in and polycrystalline samples have been identified by differential extended x-ray absorption fine structure (DiffEXAFS) spectroscopy. We demonstrate that cobalt atoms at octahedral sites are responsible for their magnetostriction. The analysis of DiffEXAFS data indicates that the local-site magnetostrictive strains of Co atoms are reversed in these two oxides, in agreement with the macroscopic magnetostriction. For the spinel, a large negative strain along the (100) direction has been determined for the octahedron causing a tetragonal contraction in contrast with the perovskite, where a positive moderate strain along the (100) direction was found resulting in a tetragonal expansion. The different local-site magnetostriction is understood in terms of the different valence and spin state of the Co atoms for the two oxides. The macroscopic magnetostriction would be explained then by the relative change in volume, either contraction in or expansion in , when the tetragonal axis of the Co site is reoriented under an externally applied magnetic field.
2 More- Received 17 June 2019
- Revised 27 August 2019
DOI:https://doi.org/10.1103/PhysRevB.100.104420
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