Atomic-scale mechanisms for magnetostriction in CoFe2O4 and La0.5

Abstract

The atomic environments involved in the magnetostriction effect in CoFe 2 O 4 and La 0.5 Sr 0.5 CoO 3 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 CoFe 2 O 4 spinel, a large negative strain along the (100) direction has been determined for the CoO 6 octahedron causing a tetragonal contraction in contrast with the La 0.5 Sr 0.5 CoO 3 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 CoFe 2 O 4 or expansion in La 0.5 Sr 0.5 CoO 3 , when the tetragonal axis of the Co site is reoriented under an externally applied magnetic field.

Anomalous Nernst Effect and Giant Magnetostriction in Microwave-Synthesized La0.5Sr0.5CoO3

“…As the 3d-orbitals are coupled to the lattice via crystal field interaction, the lattice expands along the field direction. Very recently, Subi ́as et al 52 carried out differential X-ray absorption in La 0.5 Sr 0.5 CoO 3 and CoFe 2 O 4 with and without an external magnetic field and concluded that the Co−O bond length along the [100] axis elongates under a magnetic field in La 0.5 Sr 0.5 CoO 3 , whereas it shrinks in CoFe 2 O 4 . The elongation is consistent with the observation we made here.…”

Strain-magneto-optics in CoFe2O4: Magneto-absorption in Voight geometry

“…It was assumed in Ref.9 that this band is related to electronic transitions from the valence band into the VО+3d(Fe 3+ ) state, where VО denotes an oxygen vacancy. However, it was recently shown 25 that the oxygen environment of the Co 2+ and Fe 3+ ions experiences octahedral distortions, which are stronger in the case of Co 2+ . We can assume that the band (1) is formed by the transitions into the VО+3d(Fe 3+ ) or/and VО+3d(Co 2+ ) states.…”

Sharp steps in magnetization, magnetoresistance, and magnetostriction in Pr0.6Sr0.4Co1−yGayO3

“…5 Exploration of magnetotransport in hole-doped rare-earth cobaltites other than R=La did not evoke much enthusiasm among researchers because the magnitude of MR at T=TC decreases with decreasing size of R 3+ or divalent alkaline earth ions. 6,7,8,9 An intriguing property of cobaltites is the existence of giant anisotropic magnetostriction in La1-xSrxCoO3 series (x=0.3-0.5) attributed to magnetic field-induced spin-state transition of Co ions at low temperatures, 10,11,12 however, magnetostriction in other rare-earth cobaltites is scarcely reported until now. 13,14 In this letter, we report the influence of Co-site substitution on the magnetization, magnetoresistance and magnetostriction in Pr0.6Sr0.4Co1-yGayO3 (y=0-0.3).…”