Composition Dependence of Magnetism in Single Crystal Co/Ni Dichloride Dihydrate

This mixed magnet is composed of 3D Ising (Co system) and Heisenberg (Ni system) antiferromagnets ordering at 17.2 K and 7.3 K, respectively. Ferromagnetically coupled metal-dichloride-metal...chemical and structural chains occur in each component, with antiferromagnetic interchain interactions operating. Metamagnetic transitions in the pure Co and Ni systems occur near 31 and 19 kG, respectively. Mixed magnetic single crystals have been obtained and studied for Co-rich compositions. Strong anisotropy is apparent in the susceptibility vs temperature and in the magnetization vs field. The appearance of both the easy and hard axis susceptibilities and the easy and hard axis magnetizations evolve with composition. Metamagnetic transitions are evident, but appear at much lower fields than for either pure component. There is modest composition dependence in the apparent critical field. The temperature variation of easy axis hysteresis loop areas is analyzed to suggest an activation energy for domain wall motion which varies little with composition.