Chemical Control of Spin Chirality in $(Nd_{1-x} Dy_x)_2 Mo_2 O_7$
  Magnetization and Hall resistivity have been investigated for single crystals of Dy-doped Nd$_{2}$Mo$_{2}$O$_{7}$. A sharp decrease of the Hall resistivity upon a metamagnetic transition, perhaps associated with magnetic-field ($H$) induced flop of Dy$^{3+}$ moments, has been observed in the Dy-doped crystals only for $H \parallel [111]$ direction. In addition, the sign of the Hall resistivity at a high field, both for $H \parallel [100]$ and for $H \parallel [111]$, changes with the Dy-doping. These results are explained in terms of the sign change of Mo spin chirality that is controlled by the Dy$^{3+}$ moments with a different sign of $f$-$d$ interaction from the Nd$^{3+}$ moments. 
S. Iguchi, D. Hashimoto, Y. Taguchi, and Y. Tokura