Spin disorder induced magnetization and susceptibility originating in NiO6 octahedra of nickelates

Spin disorders in NiO6 octahedra of several nickelate systems have been modeled by varying an inter-spin separation (rik) between spins of O and Ni. Using the mean field theory (MFT) we have calculated magnetization as a function of (i) temperature and (ii) rik in a wide range of H for a small ratio of D/T, where D is single ion anisotropy. Even at very low T, the saturation region in M(T) gets affected for rik = a/2. The curvature of M(T) is highly reduced with the increasing H including an almost linear variation at higher fields. With the change in single ion anisotropy M(rik) is found to be strongly affected. Dependencies of susceptibility (χ) on both (i) temperature (T) and (ii) rik have also been calculated. Possible magnetic phase transitions are identified to be sensitive to the positional spin disorder. Effect of D on susceptibility is found to be very different in nature for rik ≤ 0.2.