Unconventional anomalous hall effect enhanced by a noncoplanar spin texture in the frustrated kondo lattice Pr2Ir2O7

We have investigated the Hall effect in the geometrically frustrated Kondo lattice Pr2Ir2O7. In its spin-liquid-like paramagnetic regime, the Hall resistivity ρxy is found to increase logarithmically on cooling. Moreover, in this low temperature region, the field dependence of the Hall conductivity σxy shows a large enhancement up to 30Ω-1cm-1 as well as a nonmonotonic change with the magnetization. Our results are far different from the anomalous Hall effect due to the spin-orbit coupling observed in ordinary magnetic conductors. We discuss the possible spin-chirality effect in the Ir 5d conduction band due to the noncoplanar texture of Pr 111 Ising-like moments.