Magnetic and Transport Properties of Phyrochlore Molybdates

Abstract

Magnetic and transport properties of the pyrochlore molybdate R 2- x R x ′ Mo 2 O 7 (R, R ′ = rare earth, Y), which exhibits the metal-insulator (M-I) transition with varying x , have been studied. The transition from an antiferromagnetic spin-glass state to a ferromagnetic one occurs at x far from the M-I phase boundary, indicating that the intimate correlation of the magnetic state with the conducting nature is not so obvious. In Nd 2 Mo 2 O 7 , the ordering of Mo spins takes place at about 95 K, where the anomalous Hall resistivity appears with decreasing temperature T along with the spontaneous magnetization. With the ordering of Nd moments which becomes significant below ∼20 K with decreasing T , the behavior of the anomalous Hall resistivity markedly changes, while the Mo-magnetization is partially cancelled by the Nd magnetization. It is shown that the anomalous Hall resistivity can be described by two components, 4π R s M Mo and 4π R s ′ M Nd , the contributions from the uniform magnetizations M Mo and M Nd of Mo and Nd moments, respectively. The sign of R s ′ is opposite to that of R s . Brief arguments are given if the unusual behavior of the Hall resistivity is related with the nonzero chirality of the magnetic moment system.