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

We have studied a nearly stoichiometric insulating Y0.97(2)Cr0.98(2)O3.00(2) single crystal by performing measurements of magnetization, heat capacity, and neutron diffraction. Albeit that the YCrO3 compound behaves like a soft ferromagnet with a coersive force of similar to 0.05 T, there exist strong antiferromagnetic (AFM) interactions between Cr3+ 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-N = 141.5(1)K, which increases to T-N (5 T) = 144.5(1) K at 5 T. Within the accuracy of the present neutron-diffraction studies, we determined a G-type AFM structure with a propagation vector k = (1 1 0) and Cr3+ spin directions along the crystallographic c axis of the orthorhombic structure with space group Pnma below T-N. At 12 K, the refined moment size is 2.45(6) mu(B), similar to 82% of the theoretical saturation value 3 mu B. The Cr3+ spin interactions are probably two-dimensional Ising like within the reciprocal (1 1 0) scattering plane. Below T-N, the lattice configuration (a, b, c, and V) deviates largely downward from the Grfineisen 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 YCrO3 compound is probably lower than the currently assumed one. Additionally, we compared the t(2)g YCrO3 and the e(g) La7/8Sr1/8MnO3 single crystals for a further understanding of the reason for the possible symmetry lowering.