Magnetic ordering in HoB12 below and above TN

We present results of neutron scattering experiments on frustrated antiferromagnet HoB12 above and below Neel temperature TN. Diffuse scattering patterns indicate that above TN=7.4K pronounced correlations between neighboring magnetic moments of Ho-ions appear, similar to one-dimensional (1D) magnets. Moreover, the diffuse scattering patterns show a symmetry reduction from fcc to simple cubic. Analogous behavior in three dimensional (3-D) systems is not known, although it was predicted by theory. Results below TN and in applied magnetic field, on the other hand, reveal three amplitude-modulated incommensurate magnetic structures in this compound. The role of various interactions leading to this behavior (above and below TN) is being discussed. Additional attention is paid also to rho(T) resistivity dependencies in various magnetic fields close to and above the quantum critical point.