NMR analysis and the magnetic properties of GdMn 6Ge 6

Abstract

The magnetic phase diagram of GdMn 6Ge 6 was deduced from magnetisation measurements of powder samples. In agreement with the results of molecular field calculations it contains a paramagnetic phase, a ferrimagnetic phase where the magnetisation of ferromagnetically coupled Mn and Gd sublattices points in opposite directions, a spin flop phase and a phase where ferromagnetically ordered Gd and Mn planes are present, but the interaction between these planes results in a macroscopic magnetisation smaller than that in the ferri-phase. For the first time the zero-field magnetic resonance of 73Ge-nuclei has been observed at 77 K and 4.2 K. A separation of the Zeeman and quadrupolar contributions yields the hyperfine fields and the electric field gradients at the three inequivalent Ge sites. The enhancement observed indicates the presence of some net magnetisation in the low-temperature zero-field phase. Applying an external magnetic field, the sign of the hyperfine field at the Ge nuclei was determined.