ANISOTROPIC SPECIFIC-HEAT OF CONB2O6 IN MAGNETIC-FIELDS

We investigated the successive magnetic phase transitions of CoNb2O6 at 2.9 K and 1.9 K by measuring the specific heat, magnetic susceptibility and magnetization Of poly- and single-crystalline samples. The specific heat measurements performed in external magnetic fields up to about 1.5 kOe disclosed the Ising-like nature of the transitions and tremendous anisotropic magnetic-field dependence due to the low-dimensional character. Moreover, the specific heat and ac magnetic susceptibility data imply another magnetic state below 1 K. These consequences suggest a very interesting magnetic phase diagram, resulting from the competing single-ion anisotropy and exchange interactions in this compound.