Disorder in Co-Cu granular alloys studied by 59Co NMR

Abstract

We have performed59Co zerofield nuclear magnetic resonance (NMR) experiment at 4 K onCox−Cux1(x= 0.10, 0.32 and 0.76) nanogranular alloys. The NMR signalarises from Co rich ferromagnetic clusters formed within the Cu matrix. The analysis of NMR spectra shows that the resonance peaks arise from bothfccandhcpphases of Co. However, Co nuclei experience magnetic hyperfinefield from Co only environment as well as other environments in which nearest-neighbor (NN)Coatoms are replaced by Cu. Assuming that these two environments constitute the core and the shell of the Co clusters, it is estimated using previous magnetizationmeasurements that the contribution of core dominates in the ferromagnetism of the particles though it occupies only about 20% of the volume of Co clusters even forhigh Co containing alloys