Magnetic susceptibility of Nd (BrO3)3⋅9H2O single crystal: Effects of the crystal field and calculation of the electrostatic crystal field parameters

Abstract

Single crystals of neodymium bromate were grown and their principal magnetic susceptibility and anisotropy determined from 90 to 300K. The anisotropy, which is relatively small, decreases with lowering of temperature and suffers a reversal at ∼155 K. The magnetic moment peff shows a small linear variation with temperature. A least squares fit yields Curie constant C=1.666 and paramagnetic Curie temperature θ=−23.76 K for χ̄. The results were analyzed with one electron crystal field (CF) with the intermediate coupling reduced matrix elements. Inclusion of J mixing through the CF with all the 4I J manifolds leads to a considerable change in the Stark energies and the magnetic properties. A theoretical analysis of the observed optical absorption and magnetic data shows conclusively that the next nearest neighbor interactions which reduce the Nd3+ site symmetry to C3v do have a significant role to play. The effects of the CF on the thermal and hyperfine behavior of Nd3+ in bromate lattice have been worked out. An ab initio calculation of the CF parameters using the structural data on the crystal demonstrates the inherent weakness of the point charge treatment to account for the effective parameters obtained from experiments. Although it is felt that the factors primarily responsible for the discrepancy are the uncertainties in the structural data and in the exact location of the dipole and charge centers, this by no means discounts the importance of overlap and covalency.