Giant magnetoresistance in granular ferromagnetic systems of Ni3Mn alloy

Giant magnetoresistance (GMR) phenomena were investigated in the inhomogene ous phase of Ni3Mn alloy, where magnetically ordered single-domain clusters are distributed in a disordered nonmagnetic matrix. The observed GMR varie s with the long-range-order parameter S and has values ranging from -0.5% t o -1.8% for 0.1 < S < 0.5. The GMR is proportional to [1 - (M/M-S)(2)] with an applied magnetic field, where M and M-S are the global and saturation m agnetizations, respectively. We found that the GMR is correlated with the a verage size [m] and the volume fraction epsilon of the ferromagnetic cluste rs. The GMR is maximized at [m] similar to 3(3) nm(3) and epsilon similar t o 0.25, these values being obtained from analysis using a superferromagneti c model.