CORRELATION BETWEEN THE STRUCTURE AND PARAMAGNETIC-SUSCEPTIBILITY OF NDOF

The high-resolution X-ray powder diffraction patterns on the polycryst alline NdOF were measured at selected temperatures between 6 and 295 K . The hexagonal unit cell constants a and c first decrease as a functi on of temperature as anticipated down to ca. 50 K but then suddenly a increases and c decreases strongly, The cell volume remains constant, however. The compression of the lattice in the direction parallel to t he c-axis is due to the high anisotropy of the NdOF lattice. The rigid NdO+ complex cation prevents the compression in the plane perpendicul ar to the c-axis and results in a slight dilatation in the plane. The experimental paramagnetic susceptibility measured between 3 and 850 K shows also an anomalous behavior around 50 K indicating that the struc tural changes influence the magnetic properties as well. The evolution of the paramagnetic susceptibility as a function of temperature was w ell simulated below 50 K by wave functions and energy level values obt ained from inelastic neutron scattering measurements at 2.5 K. Above 5 0 K the simulation fails because of structural changes. The high aniso tropy of the NdOF lattice was concluded to be responsible also for the anomalous behavior of the paramagnetic susceptibility as a function o f temperature. (C) 1998 Elsevier Science S.A.