Magnetic structure of rare-earth dodecaborides

We have investigated the magnetic structure of HoB12, ErB12 and TmB12 by neutron diffraction on isotopically enriched single-crystalline samples. Results in zero field as well as in magnetic field up to 5T reveal modulated incommensurate magnetic structures in these compounds. The basic reflections can be indexed with q=(1/2+/-δ, 1/2+/-δ, 1/2+/-δ), where δ=0.035 both for HoB12 and TmB12 and with q=(3/2+/-δ, 1/2+/-δ, 1/2+/-δ), where δ=0.035, for ErB12. In an applied magnetic field, new phases are observed. The complex magnetic structure of these materials seems to result from the interplay between the RKKY and dipole-dipole interaction. The role of frustration due to the fcc symmetry of dodecaborides and the crystalline electric field effect is also considered