Processing-structure correlations of Ni-Fe-Cu-Cr soft magnetic alloy

Nickel-based alloy is an important class of magnetic materials that have high permeability, large saturation and remnant magnetization, low hysteresis loss and low coercivity. These properties vary with the grain size, shape, magnetic domains and orientation. As the grain approaches nanoscale, an important averaging of the magnetocrystalline anisotropy over many grains coupled within an exchange length results in a significant increase of the magnetic softness and the effect of the internal thermal energy becomes more pronounced. The crystalline Ni-Fe-Cu-Cr system processed by high-energy ball milling (HEBM) and metal injection moulding (MIM) were investigated using TEM and SEM. The average grain size of the HEBM samples was found to be in the order of several tens of nanometers while those of the MIM are in the order of tens of micrometers. The magnetic properties of the HEBM and MIM samples were also investigated. The magnetic properties of the HEBM samples are significantly 'softer' magnetically when compared to the MIM samples. The coercivity (H_c) of MIM sample is 37.5 Oe while the HEBM sample is 17.5 Oe. More remarkably, the initial permeability (μ_iμ) of the HEBM sample is an order higher than the MIM sample 2184 and 225 Oe respectively.