μSR study of the S=1/2 triangular lattice antiferromagnet AgNiO2

AgNiO2, a model compound of an S=1/2 triangular lattice, was studied by muon spin relaxation in addition to ac, dc susceptibility, electrical resistivity and neutron diffraction. The relaxation rate shows a sharp peak at around TN=28 K followed by a sudden decrease of initial asymmetry indicating a magnetic ordering. Three internal fields ranging from 0.2 to 0.3 T were obtained from the muon precession period. However, a neutron diffraction experiment failed to detect any magnetic order at low temperatures. From these results, it was concluded that magnetic coherence is confined to small domain compared with the coherence length of neutron diffraction due to spin frustration.