Magnetic Structure of Rare-Earth Dodecaborides

We have investigated the magnetic structure of HoB 12 , ErB 12 and TmB 12 by neutron diffraction on isotopically enriched single-crystalline samples. Results in zero field as well as in magnetic field up to 5 T 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 HoB 12 and TmB 12 and with q = (3/2±δ, 1/2±δ, 1/2±δ), where δ = 0.035, for ErB 12 . 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.