Magneto-optical and magnetization studies in the rare-earth orthochromites. VI. NdCrO3

Abstract

Single crystals of NdCr${\mathrm{O}}_{3}$ were studied by means of bulk magnetization, susceptibility, and optical-absorption spectroscopy measurements. This compound orders at ${T}_{N}=214$ \ifmmode^\circ\else\textdegree\fi{}K in a ${\ensuremath{\Gamma}}_{2}({F}_{x})$ canted antiferromagnetic spin structure which persisits down to ${T}_{R}=35$\ifmmode^\circ\else\textdegree\fi{}K. At ${T}_{R}$ a first-order Morin-type phase transition occurs and, down to below 4.2\ifmmode^\circ\else\textdegree\fi{}K, the spins are in the antiferromagnetic ${\ensuremath{\Gamma}}_{1}(0)$ mode. The temperature dependence of the spontaneous magnetization above ${T}_{R}$ is significantly different from that of other rare-earth orthochromites and is reminiscent of that found in some ferrimagnetic materials. Using a single-ion model in the molecular-field approximation, it is shown that this behavior is due to magnetization contributions from the two lowest Kramers's doublets of the ${\mathrm{Nd}}^{3+}$ ground multiplet. The calculated Stark splitting is 97\ifmmode\pm\else\textpm\fi{}15\ifmmode^\circ\else\textdegree\fi{}K, in excellent agreement with the absorption spectroscopy measurements. Above ${T}_{R}$, the ground-doublet splitting is essentially due to the Nd-Cr interaction, while below ${T}_{R}$ the additional polarization due to Nd-Nd coupling becomes significant.