Magnetic ordering in the ternary phosphides Tb2Fe12P7, Tb2Co12P7, Tb2Ni12P7 and Ho2Ni12P7

The ordering of the magnetic moments of the lanthanide atoms in the hexagonal phosphides Tb2T12P7 (T = Fe, Co, Ni) and Ho2Ni12P7 has been investigated by SQUID measurements and neutron powder diffraction. In Tb2Co12P7 the magnetic moments of both the Tb3+ ions and the cobalt atoms are ferromagnetically ordered below T-c = 150 K. In contrast to this compound, the transition metal atoms in Tb2Fe12P7, Tb2Ni12P7 and Ho2Ni12P7 carry virtually no magnetic moments. In Tb2Fe12P7 the terbium moments show below T-N = 4.5(5)K a triangular spin arrangement within the ab-plane with the wave vector k = (1/3 1/3 0). For the lanthanide atoms in Tb2Ni12P7 and Ho2Ni12P7 a collinear antiferromagnetic order was found below T-N = 12.5(5)K and T-N = 10.0(5) K. (C) 1998 Elsevier Science B.V. All rights reserved.