Huge anisotropic magnetostriction inLa1−xSrxCoO3−δ(x>~0.3):Field-induced orbital instability

Abstract

Magnetostriction parallel and perpendicular to the applied magnetic field has been measured for ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CoO}}_{3}$ $(x=0.3, 0.5)$ over a wide temperature range $(4.2<~T<~300$ K) and up to a maximum field of 14.2 T. We find a huge anisotropic magnetostriction $({\ensuremath{\lambda}}_{t})$ with values as large as $2.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ for $x=0.3$ and $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ for $x=0.5$ at 14.2 T and temperatures below 100 K. The volume magnetostriction has been found to be negligible. The large value of ${\ensuremath{\lambda}}_{t}$ cannot be explained on the basis of the usual spin-orbit-coupling contribution. We propose that such a huge anisotropic magnetostriction has its origin in the orbital instability of the trivalent Co ions under the magnetic field, giving rise to a transition from a nondegenerated low-spin state to an orbital degenerated intermediate-spin state.