Magnetic structure and glassiness in Fe_0.5Ni _0.5PS₃

This work explores the magnetic properties of Fe_0.5Ni _0.5PS₃. The system shows pronounced hysteresis in the magnetic phase transition temperature as a function of the direction of the change in temperature. Field cooled/zero field cooled hysteresis is not pronounced. However, the transition temperature between antiferromagnetic and paramagnetic order occurs at approximately 97 K on cooling, but at 138 K on warming, whether the warming is after zero field or field cooling. This is indicative of magnetic glassiness, and made all the more unusual because all measurements exhibit a transition to a third magnetic phase existing at temperatures below ∼14K. The intermediate phase relaxes on a laboratory time scale of the order of 48 min, into an antiferromagnetic state whose magnetic structure is, from neutron diffraction, indistinguishable from the low temperature state. This low temperature state shows magnetic ordering consistent with that observed in CoPS₃ and NiPS₃. Analysis of the neutron measurements shows that the direction of moments cannot be along the b-axis. It is also shown that the moments are unlikely to lie in the c ^* direction. Therefore, we suggest that the moments lie along the a-axis.