Magnetic anisotropy of spin tetramer system SeCuO$_3$ studied by torque magnetometry and ESR spectroscopy

TL;DR

This study investigates the magnetic anisotropy of SeCuO₃ using torque magnetometry and ESR spectroscopy, revealing temperature-dependent anisotropic exchange interactions and spin-lattice coupling in the spin tetramer system.

Contribution

It provides experimental evidence of anisotropic exchange interactions and detailed magnetic axis behavior in SeCuO₃, which was not previously characterized.

Findings

Macroscopic magnetic axes rotate with temperature above 50 K

ESR linewidth indicates presence of anisotropic exchange interactions

System exhibits antiferromagnetic order below 8 K with spin-lattice coupling

Abstract

We present an experimental study of macroscopic and microscopic magnetic anisotropy of a spin tetramer system SeCuO$_3$ using torque magnetometry and ESR spectroscopy. Large rotation of macroscopic magnetic axes with temperature observed from torque magnetometry agrees reasonably well with the rotation of the $\textbf{g}$ tensor above $T \gtrsim 50$~K. Below 50~K, the $\textbf{g}$ tensor is temperature independent, while macroscopic magnetic axes continue to rotate. Additionally, the susceptibility anisotropy has a temperature dependence which cannot be reconciled with the isotropic Heisenberg model of interactions between spins. ESR linewidth analysis shows that anisotropic exchange interaction must be present in SeCuO$_3$. These findings strongly support the presence of anisotropic exchange interactions in the Hamiltonian of the studied system. Below $T_N=8$~K, the system enters a long - range antiferromagnetically ordered state with easy axis along the $<\bar{1} 0 1>^*$ direction. Small but significant rotation of magnetic axes is also observed in the antiferromagnetically ordered state suggesting strong spin-lattice coupling in this system.