MAGNETIC-ORDERING IN PYROCHLORE HO2MN2O7

The magnetic susceptibility of Ho2Mn2O7 With a spontaneous rise below about 40 K and a paramagnetic Curie temperature of +39 K suggests a fe rromagnetic ordering. Indeed neutron diffraction profiles show strongl y enhanced Bragg peaks with a temperature dependence which indicates a n apparent T-c approximate to 35 K. Nonetheless, the magnetic diffract ion pattern is not consistent with a collinear ferro or ferrimagnetic ordering of the Ho3+ and Mn4+ sublattices. Furthermore, specific heat and small angle neutron scattering (SANS) show features which are also incompatible with conventional long-range order. (C) 1996 American In stitute of Physics.