Magnetic frustration in the spinel compounds GeNi2O4 and GeCo2O4 -: art. no. 10A512

In the spinel compounds AB(2)O(4), the B sites form a pyrochlore lattice. GeCo2O4 and GeNi2O4 have been investigated using high magnetic field magnetization as well as neutron diffraction measurements. Both compounds become antiferromagnetic at low temperature (around 23 and 12 K, respectively) with the same propagation vector. The magnetization then presents two spin flop fields and one huge saturation field (above 50 T). The Curie-Weiss temperature is positive for the Co spinel and negative for the Ni one. A model taking into account the first neighbor interaction J(1) together with two different third neighbor interactions J(2) and J(3) is able to account for the common observed magnetic behavior. J(1) is ferromagnetic while J(2) and J(3) are antiferromagnetic, in agreement with Goodenough-Kanamori-Anderson rules. These competing interactions are responsible for the frustration in these compounds. (c) 2005 American Institute of Physics.