Structure And Properties Of The Integer-Spin Frustrated Antiferromagnet Geni2o4

We report the results of magnetic susceptibility, specific heat, synchrotron x-ray, and neutron powder diffraction measurements for the normal spinel GeNi2O4, which becomes antiferromagnetic below a Neel temperature (T-N) of 12 K. The Neel transition occurs in two discrete steps, separated in temperature by 0.6 K. The total magnetic entropy evaluated from the specific heat data is only similar to1/2 of the expected 2R ln 3 per mole of GeNi2O4. The specific heat data also suggest the presence of both gapless and gapped excitations within the Neel state. GeNi2O4 remains cubic to temperatures well below T-N.