Anomalous Hall effect of pyrochlore molybdate Nd2Mo2O7

Hall resistivity rho (H) has been investigated for single crystals of pyroc hlore molyhdate Nd2Mo2 O-7. With decreasing temperature T, the anomalous Ha ll 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 describe d by the well-known equation rho (H) = R0H + 4 piR(s)M, where R-0 and R-s a re 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 neutro n diffraction studies carried out by the present authors' group, induces ma rked change in the behavior of the anomalous part of pH. The behavior in th e low temperature region has been found to be simply described by the equat ion rho (H) = R0H + 4 piR(s)M(Mo) + 4 piR(s)M(Mo) where M-Mo and M-Nd are t he 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 f or ordinary ferromagnets and might be related to the nonzero spin chirality observed in the present system.