A NEUTRON-DIFFRACTION DETERMINATION OF THE MAGNETIC-PROPERTIES OF BARIUM HOLMIUM FLUORIDE, BAHO2F8

A previous study of single crystals of monoclinic barium holmium fluor ide, BaHo2F8, has shown that, as a result of crystal held splittings, the ground state of the Ho3+ ion, 4f(10), I-5(8), is a non-Kramers dou blet, with a single g value of 14.24, parallel to the crystallographic a axis. A transition to an antiferromagnetically ordered state occurs at about T-N = 1.76 K but the precise nature of the magnetically orde red state cannot be determined from these measurements alone. This pap er describes the results of a neutron diffraction investigation from 4 .2 K down to 0.3 K. An initial measurement on a powdered sample at 0.3 1 K was sufficient to determine which of three group theoretically all owed magnetic arrangements is present; the structure determined is ant iferromagnetic with a(10 1/2) magnetic propagation vector.