Magnetic properties and structures of RZn12 compounds

The magnetic properties of RZn12 compounds have been studied between 1.5 and 300 k, and the magnetic structures have been determined by neutron diffraction. For all these compounds the low-field susceptibility shows a maximum which is characteristic of a Neel temperature between 16.5K for GdZn12 and 2.4 K for HoZn12. Well above Tsub(N), this susceptibility obeys a Curie-Weiss law; the paramagnetic moment approximates to the free-ion value. The results are in good agreement with those previously obtained for some of these compounds. Below Tsub(N) the magnetization curves have been studied up to 150 kOe. A large number of satellite lines characterize the neutron-diffraction patterns below the Neel temperature. All the propagation vectors are of the type tau [1/2, 1/2, tau]. For TbZn12 a sinusoidally modulated structure is observed (tau = 0.29). In the erbium compound (a Kramer ion) the magnetic cell is commensurate with the crystallographic cell (tau = 0.25) and the magnetic moments are parallel to the c axis. In HoZn12, the non-collinear structure is indexed with two propagation vectors. A transition is observed at 2K; at lower temperatures the magnetic cell is commensurate with the crystallographic cell. Competition appears between predominantly negative long-range magnetic interactions. The crystal-field potential affects the values of the magnetic moments and the ordering temperatures. (author)