Proton NMR study of randomly diluted magnet MnxCd1−x(HCOO)2·2(NH2)2CO

Abstract In the diluted magnetic system Mn x Cd 1− x (HCOO) 2 ·2(NH 2 ) 2 CO, the temperature dependence of the proton NMR spectra shows no clear anomalies at the Neel temperature. With increasing temperature, the width of the NMR spectral line gradually decreases. This phenomenon is observed even at temperatures above the Neel temperature. In addition, the spectral shape does not sharpen abruptly at the percolation threshold x p , which is the critical concentration for the magnetic long-range order to (dis)appear. These results strongly suggest the existence of Griffiths phase, in which some of the ordered spin clusters slowly fluctuate and have a finite value of the magnetic moments thermally averaged over the whole system.