Antiferromagnetism of Iron in Face-Centered Crystalline Lattice and the Causes of Anomalies in Invar Physical Properties

The anomalies of electrical and magnetic properties in invars at low temperatures and the fact that these anomalies are observed in Fe-Ni alloys with the nickel content ranging from 30 to 40% are explained on the grounds of an assumption that the exchange integral of electrons of neighboring ions of iron in a face-centered lattice is negative which entails a “latent” antiferromagnetism in the invars. This assumption is founded on experimental data obtained by authors and proving that in an Fe alloy with a face-centered lattice, stable at low temperatures thanks to the presence of chromium and nickel alloying elements, an antiferromagnetic transformation occurs. The paper presents results of investigation of the influence of pressure upon the magnetic saturation ${\sigma }_s$ and the residual resistivity ${\rho }_0$ of iron, nickel and Fe-Ni alloys at low temperatures. It is shown that the values $K_{\sigma }{\text{\hspace{0.17em}=\hspace{0.17em}(1/σ}}_s{\mathrm{)\hspace{0.17em}(\Delta \sigma }}_s\mathrm{/\Delta P)}$ and $K_{\rho }{\text{\hspace{0.17em}=\hspace{0.17em}(1/ρ}}_0\mathrm{)\hspace{0.17em}(\Delta \rho /\Delta P)}$ in invar alloys at low temperatures and other Fe-Ni alloys; the ratios $K_{\rho }{\mathrm{/K}}_{\sigma }$ are approximately equal to the ratios ${\text{(1/}}_{\text{ρ0}}{\mathrm{)\hspace{0.17em}(\Delta }}_{\text{ρ0}}{\text{/ΔH)\hspace{0.17em}/(1/}}_{\mathrm{\sigma s}}{\mathrm{)\hspace{0.17em}(\Delta }}_{\mathrm{\sigma s}}\mathrm{/\Delta H)}$ , which is in agreement with the conclusions of the suggested theory.