Antiferromagnetic spin structure and negative thermal expansion of Li2Ni(WO4)2

We report the results of a study on the crystal and magnetic structure of Li2Ni(WO4)2 with a neutron diffraction technique. The Ni2+ spins of S = 1 for NiO6 octahedra are coupled via corner-sharing, nonmagnetic double tungstate groups in a super-superexchange route. Two magnetic anomalies at TN1∼ 18 K and TN2∼ 13 K are revealed from the measured magnetic susceptibility χ(T), and TN2 is confirmed to be the onset of a commensurate long-range antiferromagnetic (AF) ordering through neutron diffraction. A negative thermal expansion phenomenon is observed below TN2, which has been interpreted as a result of competing normal thermal contraction and long-range AF spin ordering through counterbalanced WO4 and NiO6 polyhedral local distortion. The AF spin structure has been modeled and used to show that Ni spins with a saturated magnetic moment of ∼1.90(27)μB that lies in the a−c plane approximately 46∘(±10∘) off the a axis. The experimental results are compared and found to be consistent with theoretical calculations using density-functional theory with a generalized gradient approximation plus on-site Coulomb interaction. ©2015 American Physical Society

Keywords

Antiferromagnetism, Thermal expansion, Neutron diffraction, Crystal structure, Magnetic moments, Spin

Citation

Karna, S. K., Wang, C. W., Sankar, R., Avdeev, M., Singh, A., Panneer Muthuselvam, I., Singh, V. N., Guo, G. Y., & Chou, F. C. (2015). Antiferromagnetic spin structure and negative thermal expansion of Li2Ni(WO4)2. Physical Review B, 92(1), 014413. doi:10.1103/PhysRevB.92.014413