Jae Wook Kim, Y. Kamiya, E. D. Mun, M. Jaime, N. Harrison, J. D. Thompson, H. T. Yi, Y. S. Oh, S. -W. Cheong, C. D. Batista, V. S. Zapf
We study the magnetic field ($H$)-induced behavior of the multiferroic material Ca$_3$Co$_{2-x}$Mn$_{x}$O$_6$ ($x$$\sim$0.97) by measuring magnetization ($M$), magnetostriction ($\Delta$$L/L$), electric polarization ($P$), and magnetocaloric effect (MCE). We measured $M$ and $\Delta$$L/L$ up to magnetic fields of $\mu_{0}H$$\simeq$92 T, which is beyond the saturation of the magnetic moments. On the controversial topic of the spin states of Co$^{2+}$ and Mn$^{4+}$, we find evidence for $S$=3/2 in both Co$^{2+}$ and Mn$^{4+}$ spins with no magnetic field-induced spin-state crossovers. Our data also reveal a regime at 25 T$\leq$$\mu_{0}H$$<$85 T in which the physical properties evolve smoothly, in contrast to the behavior below 25 T that shows step-like behavior and hysteretic. There is a linear slope in the background of $M$($H$) for both $H$$\parallel$$ab$ and $H$$\parallel$$c$, which implies that Mn$^{4+}$ spins are quasi-isotropic and develop components in the $ab$-plane in applied magnetic fields that cant until saturation at 85 T whereas the Ising Co$^{2+}$ spins saturate by 25 T. These observations show that although this compound shows some of the hallmarks of axial next-nearest neighbor Ising (ANNNI) physics at low fields, it cannot be described by the classic ANNNI model, and models need to take into account the coexistence of Ising and quasi-isotropic spins.
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http://arxiv.org/abs/1305.6892
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