Giant magnetoresistance in granular ferromagnetic systems of Ni3Mn alloy

Giant magnetoresistance (GMR) phenomena were investigated in the inhomogeneous phase of Ni3Mn alloy, where magnetically ordered single-domain clusters are distributed in a disordered nonmagnetic matrix. The observed GMR varies with the long-range-order parameter S and has values ranging from -0.5% to -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 magnetizations, respectively. We found that the GMR is correlated with the average size [m] and the volume fraction epsilon of the ferromagnetic clusters. The GMR is maximized at [m] similar to 3(3) nm(3) and epsilon similar to 0.25, these values being obtained from analysis using a superferromagnetic model.