Low-temperature magnetic properties of three linear S=1 ferromagnets with an easy plane anisotropy: TMNB, TMNC and CsNiF3

The magnetic susceptibilities parallel and perpendicular to the chain axis have been measured in the three linear ferromagnets TMNC, TMNB and CsNiF 3 between 1.2 and 77K. Strong anisotropy is observed at low temperature. The variation of chi //c with temperature is in good agreement with the predictions of the quantum given by de Neef. This allows a determination of the parameters J and D in these salts: in CsNiF 3 J=10+or-0.5K, D=8.5+or-0.5K; in TMNC, J=1.7+or-0.3K, D=3.4+or-0.5K; in TMNB, J=4.8+or-0.2K, D=3.4+or-0.5K. In the 3D long-range ordered state, a study of the variation with temperature of the spontaneous sublattice magnetisation has been performed by NMR; the curves reflect the existence of an anisotropy in the ab plane in TMNC and TMNB, but not in CsNiF 3 .