Crystal and magnetic structure of antiferromagnetic HoAuGe

HoAuGe was prepared from the elements by are melting and subsequent anneali ng at 1070 K. Its crystal structure was refined from single-crystal xray di ffractometer data: a = 440.10(5) pm, c = 723.26(9) pm, V 0.1213(1) nm(3), w R2 = 0.0640, 225 F-2-values and ten variables. The nuclear structure was co nfirmed by neutron powder diffraction. HoAuGe adopts the NdPtSb-type struct ure. The gold and germanium atoms form two-dimensional infinite: [AuGe] pol yanions with intralayer Au-Ge distances of 260.5 pm, while the interlayer A u-Ge distances of 304.1 pm are much longer. The polyanions are separated by the holmium ions. Magnetic susceptibility, specific heat capacity and neut ron diffraction measurements reveal antiferromagnetic ordering at TN = 5.6( 2) K with further magnetic reordering at T-1 = 3.5(2) K and T-2 = 2.4(2) K. At higher temperatures Curie-Weiss behaviour is observed With mu (exp)(eff ) = 10.2(2) mu (B) and circle dividep = 0(1)K. From the magnetic specific h eat a fourfold fourfold-degenerate ground state is found. The magnetic stru cture at 1.3 K is described by the propagation vector (k) over bar = (1/2, 0, 0) with the Ho spins oriented within the be-plane. As the temperature in creases towards T-N, the magnetic structure becomes incommensurate, which a ccounts for the observed additional transitions below T-N.