SINGLET-GROUNDSTATE MAGNETISM IN TBP .1. STATIC MAGNETIC-PROPERTIES

Elastic neutron scattering and magnetic susceptibility data are reported for temperatures around the Neél-point, TN=7.3 K, and for zero magnetic field. Above TN, the temperature dependence of the magnetic central peak intensity can adequately be described within the RPA assuming isotropic exchange between nearest and next-nearest neighbours as the only parameters. This two-parameter model is quantitatively confirmed by the susceptibility data. At TN, magnetic Bragg-intensities arise almost discontinuously (reaching 70% of the saturation within 0.1 K) accompanied by thermal hysteresis. For all temperatures below TN the sublattice magnetic moment is explained by solutions of meanfield equations, if an effective quadrupole-quadrupole interaction is included. The quadrupolar coupling parameter is fully consistent with a value determined recently from the softening of the c44-mode. These results show, that earlier suggestions of renormalization group results upon the origin of the first order phase transition in TbP are not needed. © 1979 Springer-Verlag.