Multiferroicity with coexisting isotropic and anisotropic spins in Ca3Co2-xMnxO6

Abstract

We study magnetic and multiferroic behavior in Ca3Co2−xMnxO6 (x∼ 0.97) by high-field measurements of magnetization (M), magnetostriction [L(H)/L], electric polarization (P), and magnetocaloric effect. This study also gives insight into the zero- and low-magnetic-field magnetic structure and magnetoelectric coupling mechanisms. We measured M and ΔL/L up to pulsed magnetic fields of 92 T, and determined the saturation moment and field. On the controversial topic of the spin states of Co2+ and Mn4+ ions, we find evidence for S=32 spins for both ions with no magnetic-field-induced spin-state crossovers. Our data also indicate that Mn4+ spins are quasi-isotropic and develop components in the ab plane in applied magnetic fields of 10 T. These spins cant until saturation at 85 T, whereas the Ising Co2+ spins saturate by 25 T. Furthermore, our results imply that the mechanism for suppression of electric polarization with magnetic fields near 10 T is flopping of the Mn4+ spins into the ab plane, indicating that appropriate models must include the coexistence of Ising and quasi-isotropic spins.