Hall resistivity ρH has been investigated for single crystals of pyrochlore molybdate Nd2Mo2O7. With decreasing temperature T, the anomalous Hall effect appears at around the Curie temperature TC (∼95K). In the relatively high temperature region (T > 60K), ρH can be described by the well-known equation ρH = R0H + 4πRsM, where R0 and Rs 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 Nd 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 ρH. The behavior in the low temperature region has been found to be simply described by the equation ρH = R0H + 4πRsMMo + 4πR′sMNd, where MMo and MNd are the net magnetizations of the Mo- and Nd-moments, respectively. This result and the T-dependence of Rs 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.
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