High-Field Magnetostriction of the Spin-State Transition Compound LaCoO3

The transverse and longitudinal magnetostrictions of LaCoO 3 have been measured in pulsed magnetic fields of up to 35 T in the temperature range between 4.2 and 300 K. The magnetostrictions are proportional to the squared magnetic field of up to B 0 =25 T. The magnetostrictions at B < B 0 are analyzed with a spin-state transition model involving a nonmagnetic ground state and a magnetic excited state for Co ions where Co ions in the latter have a larger optimum lattice volume than those in the former. The observed magnetostrictions are well interpreted by the excited state with g =3.35 and the excitation energy of Δ=140 K, which are consistent with those obtained in an electron spin resonance study [Noguchi et al. : Phys. Rev. B 66 (2002) 094404] but do not reproduce the observed magnetization. The analysis based on the model and a comparison of the present data to the pressure dependence of the magnetization suggest that the elastic energy represented in terms of only the lattice volume is insufficient for the quantitative description of magnetoelastic phenomena in LaCoO 3 . A sharp increase in the longitudinal magnetostriction with a large hysteresis observed in B > B 0 and T > 60 K is ascribed to a change in the domain structure of the twinned LaCoO 3 crystal induced by a magnetic field.