Anomalous Hall effect of pyrochlore molybdate Nd2Mo2O7

Hall resistivity rho (H) has been investigated for single crystals of pyrochlore molyhdate Nd2Mo2 O-7. With decreasing temperature T, the anomalous Hall effect appears at around the Curie temperature T-C (similar to 95 K). In the relatively high temperature region (T > 60 K), rho (H) can be described by the well-known equation rho (H) = R0H + 4 piR(s)M, where R-0 and R-s are the ordinary and anomalous Hall coefficients, respectively, and M is the net magnetization predominantly contributed by the Mo spins. With further decreasing T, the ordering of the nTd moments, which is confirmed by neutron diffraction studies carried out by the present authors' group, induces marked change in the behavior of the anomalous part of pH. The behavior in the low temperature region has been found to be simply described by the equation rho (H) = R0H + 4 piR(s)M(Mo) + 4 piR(s)M(Mo) where M-Mo and M-Nd are the net magnetizations of the Mo- and Nd-moments, respectively. This result and the T-dependence of R-s and R-s' are quite different from those known for ordinary ferromagnets and might be related to the nonzero spin chirality observed in the present system.