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Heat capacity data of U 3 Al 2 Si 3 single crystal exhibit a maximum at 38 K connected with a transition to a magnetically ordered state. For a full description of the electron part we use γ 0 = 145 mJ/mol K 2 and for the phonon part of the specific heat we used the harmonic approximation of the phonon spectrum including both the Debye model with T D = 296 K and the Einstein model with T E = 136, 249 and 438 K. The heat capacity data below the magnetic transition down to 2 K fit very well within the model introducing the energy gap A = 39 K in the dispersion relation of magnons. An upturn of the C/T(T) curve, found below T = 2 K, can not be fully attributed to the nuclear Schottky contribution. The electronic heat capacity coefficient (γ 230 mJ/mol K 2 is enhanced and varies between 0.15 K and 12 K as the square root of T.

We have studied the magnetic and electrical properties of non-stoichiometric U1+xNi1+yAl compounds. It has been shown that both the positive and negative deviations from the stoichiometry lead to suppression of magnetically ordered state, to the broadening of the phase transition and to the occurrence of a region with high degree of short range magnetic ordering between 20 K and 50 K. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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.