Long-range and short-range magnetic order in β-HoH(D)2+x (x=O and 0.12)

The magnetic ordering existing at low temperatures in the stoichiometric: dideuteride HoD2 was investigated by powder neutron diffraction. Below the Neel temperature T-2 = 6.3 K, the magnetic structure is a modulated incommensurate antiferromagnet (AF), with a slightly temperature-dependent propagation vector. From T, similar to 3 to 4 K on and down to 1.4 K, it is coexisting with a commensurate AF configuration, modulated with a propagation vector k(1) = 1/4(113). The transition at T-1 is strongly hysteretic for both configurations, which is also manifest in electrical resistivity measurements. Magnetic fluctuations [short-range order (SRO) magnetism] are observed for T>T-2 UP to nearly 45 K. The superstoichiometric compound HoD2.12 exhibits quite intense SRO magnetism below T=8 K, which seems to be related to that existing for T>T-2 in the pure dideuteride HoD2 and can be fitted in the hexagonal gamma-phase cell. Attempts to observe ordering of the excess D atoms in the octahedral sublattice of HoD2.12 below room temperature were unsuccessful despite strong indications towards such a phenomenon from resistivity and x-ray lattice-parameter measurements.