Pseudo-easy-axis anisotropy in antiferromagnetic S = 1 diamond-lattice systems

• Published in: Physical review. B 2024-11, Vol.110 (17), Article 174438
• Main Authors: Vaidya, S., Hernández-Melián, A., Tidey, J. P., Curley, S. P. M., Sharma, S., Manuel, P., Wang, C., Hannaford, G. L., Blundell, S. J., Manson, Z. E., Manson, J. L., Singleton, J., Lancaster, T., Johnson, R. D., Goddard, P. A.
• Format: Article
• Language: English
• ISSN: 2469-9950; 2469-9969
• DOI: 10.1103/PhysRevB.110.174438

We investigate the magnetic properties of S = 1 antiferromagnetic diamond-lattice, Ni X 2 ( pyrimidine ) 2 ( X = Cl ,   Br ) , hosting a single-ion anisotropy (SIA) orientation which alternates between neighboring sites. Through neutron diffraction measurements of the X = Cl compound, the ordered state spins are found to align collinearly along a pseduo-easy axis, a unique direction created by the intersection of two easy planes. Similarities in the magnetization, exhibiting spin-flop transitions, and the magnetic susceptibility in the two compounds imply that the same magnetic structure and a pseduo-easy axis is also present for X = Br . We estimate the Hamiltonian parameters by combining analytical calculations and Monte Carlo (MC) simulations of the spin-flop and saturation field. The MC simulations also reveal that the spin-flop transition occurs when the applied field is parallel to the pseduo-easy axis. Contrary to conventional easy-axis systems, there exist field directions perpendicular to the pseduo-easy axis for which the magnetic saturation is approached asymptotically and no symmetry-breaking phase transition is observed at finite fields.