The Influence of Grain Structure and Nonmagnetic Inclusions on the Magnetic Properties of High‐Permeability Fe‐Ni‐Alloys

For permalloys, the coercive force ${\mathrm{H}}_{\mathrm{c}}$ was investigated as a function of grain size and nonmagnetic inclusions. ${\mathrm{H}}_{\mathrm{c}}$ can be described as a linear unction of 3 contributions: ${\mathrm{H}}_{\mathrm{c}}\mathrm{\hspace{0.17em}=\hspace{0.17em}}{\mathrm{H}}_{\mathrm{cd}}\mathrm{\hspace{0.17em}+\hspace{0.17em}}{\mathrm{H}}_{\mathrm{cn}}\mathrm{\hspace{0.17em}+\hspace{0.17em}}{\mathrm{H}}_{\mathrm{co}}$ . ${\mathrm{H}}_{\mathrm{cd}}$ the contribution of grain boundaries, is found to be proportional to the inverse grain diameter 1/d_K. ${\mathrm{H}}_{\mathrm{cn}}$ is proportional to the number of inclusions, and ${\mathrm{H}}_{\mathrm{co}}$ , the remaining term, is probably due to magnetostrictive forces. Depending on melting and deoxidizing conditions, ${\mathrm{H}}_{\mathrm{cn}}$ is found to depend on micron‐ or submicron‐ size inclusions. As particles with a diameter s of about δ (Bloch wall thickness) should give a maximum contribution to ${\mathrm{H}}_{\mathrm{c}}$ , one has to suppose that in the second case, the submicron‐size particles give rise to stress fields of about ϱ. The different behaviour of the particles is probably due to differences in the thermal expansion coefficients of matrix and inclusions.