Magnetic-Field-Induced Transitions in Spinel GeCo2O4

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The spinel GeCo2O4 has the pyrochlore lattice of Co2+ ions, in which the kagomé and triangular planes stack alternately along the [111] direction. It shows antiferromagnetic ordering below T_{\text{N}}\sim 21 K with a characteristic wave vector of \mathbf{Q}_{M}=(1/2,1/2,1/2). The spin arrangement is ferromagnetic in the kagomé and triangular planes and antiferromagnetic between the kagomé planes as well as between the triangular planes. GeCo2O4 exhibits a magnetic phase transition at H\sim 4 T. Powder neutron diffraction measurements were performed on GeCo2O4 in ambient and magnetic field. Our results are consistent with the magnetic structure model in which the kagomé and triangular planes behave independently in magnetic field, that is, the spin arrangement between the triangular planes becomes ferromagnetic above {\sim}4 T while retaining the antiferromagnetic arrangement between the kagomé planes.
2011-03-15