Successive spin freezing behavior in a pyrochlore antiferromagnet Y2Mo2O7 under magnetic fields

Magnetic ordering of a geometrically frustrated pyrochlore antiferromagnet Y2Mo2O7 has been investigated by AC and DC magnetic measurements. A spin freezing transition at similar to 23K is indicated by AC susceptibility and low-field DC magnetization data. Under magnetic field above 700 Oe, a two-step increase of the irreversible magnetization M-irr (=M-FC - M-ZFC) is observed, corresponding to the freezing of the transverse and longitudinal spin components. The field dependence of the freezing temperatures is consistent with the H-T relations of a Heisenberg mean field spin-glass. The coefficients of the H-T relations for the longitudinal freezing are, however, fairly large compared with those of conventional disordered spin-glasses studied so far.