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

Abstract

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 σs and the residual resistivity ρ0 of iron, nickel and Fe-Ni alloys at low temperatures. It is shown that the values Kσ = (1/σs) (Δσs/ΔP) and Kρ = (1/ρ0) (Δρ/ΔP) in invar alloys at low temperatures and other Fe-Ni alloys; the ratios Kρ/Kσ are approximately equal to the ratios (1/ρ0) (Δρ0/ΔH) /(1/σs) (Δσs/ΔH),which is in agreement with the conclusions of the suggested theory.

Coexisting antiferromagnetism and ferromagnetism in mechanically alloyed Fe-rich Fe–Ni alloys: implications regarding the Fe–Ni phase diagram below 400°C

“…The antiferromagnetism of the LM g (FCC) Ferich phase is consistent with the localized moment model ''latent-antiferromagnetism'' for Invar FeNi alloys [24], which assumes an antiferromagnetic coupling between Fe-Fe nearest neighbours and a ferromagnetic one between Fe-Ni and Ni-Ni neighbours. Thus, T N for g (FCC) Fe 100Àx Ni x seems to decrease with increased Ni contents from 67 K for x ¼ 0 to B20 K for Invars at xB35 [25] and our value, T N B40 K for x ¼ 24; fits well into that trend.…”

Direct measurement of magnetization isotherms of Fe64Ni36Invar alloy in a diamond anvil cell

“…The pressure-induced strong decrease in M S (T,P) determined at pressure range up to 3 GPa agrees with measurements under hydrostatic pressures up to 1 GPa, dlnM S (5 K)/dP = −10.7 × 10 −2 GPa −1 . [2,8,17] A sharper decrease in magnetization M S (T,P) in a pressure range from 3 to 4 GPa was observed at all selected temperatures. Pressure dependence of the normalized magnetization, M S (T,P)/M 0 , is presented in Figure 3.…”

“…[2,8,10,12] Values of the pressure parameter dlnM S /dP of the Fe 69 Ni 31 alloy were reported in a range from − 12.3 × 10 −2 GPa −1 [8] at 4.2 K to the extreme values − 37 × 10 −2 GPa −1 [10] in the case of hydrostatic pressure up to 2 or − 28 × 10 −2 GPa −1 for the shock-wave compression [10] at room temperature. The value of the parameter dlnM S /dP decreases rapidly with increasing Ni-content in the FeNi Invar alloys down to − 2.5 × 10 −2 GPa −1 for the Fe 60 Ni 40 alloy [8] at 4.2 K or to − 15 × 10 −2 GPa −1 for the Fe 65 Ni 35 alloy at 295 K. [12] The value of dlnM S /dP of the Fe 65 Ni 35 alloy was also determined by indirect methods that were based on pressure measurements of magnetostriction ( − 4.7 × 10 −2 GPa −1 at 2 K), [13] the Mössbauer spectra ( − 4.4 × 10 −2 GPa −1 at 4.2 K) [14] or susceptibility in pulse field ( − 19 × 10 −2 GPa −1 at 300 K). [15] Recently, the suited techniques providing direct information on the local magnetic properties of atoms have been utilized within diamond anvil cell (DAC) pressure measurements to identify magnetic transitions in Fe-based systems and to support the mentioned theoretical models.…”

Anti-Invar properties and magnetic order in fcc Fe–Ni–C alloy

“…The magnetic order evolution is based on the Kondorski and Sedov idea about mixed exchange interactions in Fe-Ni system between atomic spins of Fe and Ni [18], the earlier Weiss model [5] and energy calculations [6] concerning an existence of different LS AF and HS FM states with the thermally induced population. In order to reveal changes in magnetic order with the temperature the Mössbauer and SANS measurements at low temperatures 150-295 K and under external magnetic field were conducted.…”