Crystalline and magnetic structures, magnetization, heat capacity and anisotropic magnetostriction effect in a yttrium-chromium oxide

Abstract

We have studied a nearly stoichiometric insulating Y${}_{0.97(2)}$Cr${}_{0.98(2)}$O${}_{3.00(2)}$ single crystal by performing measurements of magnetization, heat capacity, and neutron diffraction. Albeit that the YCrO${}_3$ compound behaviors like a soft ferromagnet with a coersive force of $\sim$ 0.05 T, there exist strong antiferromagnetic (AFM) interactions between Cr${}^{3+}$ spins due to a strongly negative paramagnetic Curie-Weiss temperature, i.e., -433.2(6) K. The coexistence of ferromagnetism and antiferromagnetism may indicate a canted AFM structure. The AFM phase transition occurs at $T_{\text{N}}=$ 141.5(1) K, which increases to $T_{\text{N}}$(5T) = 144.5(1) K at 5 T. Within the accuracy of the present neuron-diffraction studies, we determine a G-type AFM structure with a propagation vector \textbf{k} = (1 1 0) and Cr${}^{3+}$ spin directions along the crystallographic \emph{c} axis of the orthorhombic structure with space group \emph{Pnma} below $T_{\text{N}}$. At 12 K, the refined moment size is 2.45(6) ${\mu }_{\text{B}}$, $\sim$ 82\% of the theoretical saturation value 3 ${\mu }_{\text{B}}$. The Cr${}^{3+}$ spin interactions are probably two-dimensional Ising like within the reciprocal (1 1 0) scattering plane. Below $T_{\text{N}}$, the lattice configuration (\emph{a}, \emph{b}, \emph{c}, and \emph{V}) deviates largely downward from the Gr$\ddot{\text{u}}$neisen law, displaying an anisotropic magnetostriction effect and a magnetoelastic effect. Especially, the sample contraction upon cooling is enhanced below the AFM transition temperature. There is evidence to suggest that the actual crystalline symmetry of YCrO${}_3$ compound is probably lower than the currently assumed one. Additionally, we compared the $t_{2\text{g}}$ YCrO${}_3$ and the $e_{\text{g}}$ La${}_{7/8}$Sr${}_{1/8}$MnO${}_3$ single crystals for a further understanding of the reason for the possible symmetry lowering.

13 pages, 13 figures

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