Magnetism in the S=1 frustrated antiferromagnet GeNi2O4 studied using   implanted muons
  We present the results of a muon-spin relaxation study of GeNi2O4. We provide further clarification of the two transitions to the antiferromagnetic state and measure the magnetic field dependence of the heat capacity up to 14 T. Both oscillatory and relaxing signals are observed below the lower transition (at temperature $T_{N2}) in the muon-decay positron asymmetry spectra, arising from two distinct types of magnetic environment. A possible explanation is suggested in terms of the separate ordering of two magnetic subsystems, one of which does not order fully down to the lowest measured temperature. 
T. Lancaster, S.J. Blundell, D. Prabhakaran, P. J. Baker, W. Hayes,   F.L. Pratt