Single Crystal Growth, Crystallography, Magnetic Susceptibility, Heat Capacity, and Thermal Expansion of the Antiferromagnetic S = 1 Chain Compound CaV2O4

TL;DR

This study reports the synthesis, detailed structural and magnetic characterization, and analysis of the antiferromagnetic properties of single crystal CaV2O4, revealing complex magnetic transitions and interactions in an S=1 chain compound.

Contribution

It provides new single crystal growth data and comprehensive measurements, including crystallography, magnetization, heat capacity, and thermal expansion, along with modeling of magnetic interactions in CaV2O4.

Findings

Structural transition from orthorhombic to monoclinic at 108-145 K.

Long-range antiferromagnetic transition at 51-76 K.

Short-range AF ordering indicated by broad susceptibility maximum at 300 K.

Abstract

The compound CaV2O4 contains V^{+3} cations with spin S = 1 and has an orthorhombic structure at room temperature containing zigzag chains of V atoms running along the c-axis. We have grown single crystals of CaV2O4 and report crystallography, static magnetization, magnetic susceptibility \chi, ac magnetic susceptibility, heat capacity Cp, and thermal expansion measurements in the temperature T range of 1.8-350 K on the single crystals and on polycrystalline samples. An orthorhombic to monoclinic structural distortion and a long-range antiferromagnetic (AF) transition were found at sample-dependent temperatures T_S \approx 108-145 K and T_N \approx 51-76 K, respectively. In two annealed single crystals, another transition was found at \approx 200 K. In one of the crystals, this transition is mostly due to V2O3 impurity phase that grows coherently in the crystals during annealing. However, in the other crystal the origin of this transition at 200 K is unknown. The \chi(T) shows a broad maximum at \approx 300 K associated with short-range AF ordering and the anisotropy of \chi above T_N is small. The anisotropic \chi(T \to 0) data below T_N show that the (average) easy axis of the AF magnetic structure is the b-axis. The Cp(T) data indicate strong short-range AF ordering above T_N, consistent with the \chi(T) data. We fitted our \chi(T) data near room temperature by a J1-J2 S = 1 Heisenberg chain model, where J1(J2) is the (next)-nearest-neighbor exchange interaction. We find J1 \approx 230 K, and surprisingly, J2/J1 \approx 0 (or J1/J2 \approx 0). The interaction J_\perp between these S = 1 chains leading to long-range AF ordering at T_N is estimated to be J_\perp/J_1 \gtrsim 0.04.