A model of magnetic inhomogeneous structure for Fe-Ni invar alloys

The magnetic inhomogeneous structure revealed by neutron small angle scattering for Fe-Ni Invar alloys can be interpreted in terms of a model in which an effective local concentration of Fe for each atom within a sphere is taken into account in order to determine the magnetic moment of the atom.     

Pressure-induced Invar effect in Fe-Ni alloys

We have measured the pressure-volume (P-V) relations for cubic iron-nickel alloys for three different compositions: Fe 0.64Ni (0.36), Fe 0.55Ni (0.45), and Fe 0.20Ni (0.80). It is observed that for a certain pressure range the bulk modulus does not change or can even decrease to some minimum value, after which it begins to increase under still higher pressure. In our experiment, we observe for the first time a new effect, namely, that the Fe-Ni alloys with high Ni concentrations, which show positive thermal expansion at ambient pressure, become Invar system upon compression over a certain pressure range.     

Magnetic properties of rapidly quenched Fe-Ni alloys

The magnetic properties of Fe-29 at.% Ni and Fe-50 at.% Ni alloys prepared by chill block melt spinning (CMBS) have been determined and compared with those of the bulk alloys. It has been found that atomic diffusion is enhanced by CMBS and that magnetic properties can change markedly even after annealing at relatively low temperatures. The increases in T_c observed are attributed to heterogeneous short range atomic ordering.     

Phase composition and structure of Fe-Ni alloys in a unique Antarctic meteorite Yamato 791694

Phase composition and structure of iron-nickel alloys in the Antarctic meteorite Y-791694 are discussed and compared to other non-Antarctic Ni-rich ataxites using the results obtained by Mössbauer spectroscopy, X-ray diffraction and other techniques.     

Single crystalline elastic constants of Fe-Ni invar alloys

The single crystalline elastic constants of Fe-Ni alloys containing 30 – 50 wt.% Ni are reported. The anomalous temperature dependence in the ferromagnetic state is due to a large magnetic contribution to the elastic constants.     

High-field susceptibility and magnetization in Fe-Ni invar alloys

The high-field susceptibility of Fe-Ni Invar alloys does not give rise to a sudden increase at the Curie temperature. The decrease in magnetization with increasing temperature is attributed to the T² term as well as to the spin wave term for Fe-Ni Invar alloys.     

Magnetic structure of critical Fe-Ni alloys as derived from Arrott plots and Mössbauer spectra

New evidence of magnetic phase transition brought about by an external magnetic field acting on critical composition bulk Fe-Ni alloys was found by using iron-nickel alloys containing 30 wt% Ni and 31.3 wt% Ni, respectively (balance Fe). The split in the central peak of Mössbauer spectrum of the Fe-Ni alloy containing 29.7 wt% Ni, at its Curie temperature in a weak external magnetic field of 3100 Oe, is a conclusive evidence of its superparamagnetic structure.     

Mössbauer spectroscopy of Fe-Ni and Fe-Pt alloys

Mössbauer measurement on Fe-Ni and on Fe-Pt in the ordered and disordered states at various temperatures and in a longitudinal external field (H_ext = 50 kOe) have been analyzed. Hyperfine field distributions of Fe-Ni Invar alloys indicate that in addition to the ferromagnetic phase a second phase or state exists whose magnetic properties seem to be closely related to those of γ-Fe. No second phase or state was detected in the ordered Fe-Pt, while the situation in disordered Fe-Pt is uncertain.     

Temperature dependence of forced volume magnetostriction in fcc Fe-Ni alloys

The forced volume magnetostriction of the fcc Fe-Ni Invar alloys has been measured in the temperature range from 77 to 900 K to elucidate the magnetovolume effect at finite temperatures. The temperature dependence of (θ ω/θ(H/M) is evaluated as well as (θ ω/θH), where ω is the volume expansion. These results are discussed using a phenomenological model for the magnetovolume effect which takes into account the contribution of the correlation between local magnetic moments.     

Effects of pressure on magnetization of Fe-Ni and Fe-Pt invar alloys

The changes of magnetization under hydrostatic pressure up to about 20 kbar have been measured on f.c.c. Fe₆₅Ni₃₅ and f.c.c. disordered Fe₇₂Pt₂₈ Invar alloys in a pulse magnetic field up to 50 kOe with temperature down to 4.2 K. Although the pressure coefficients of the magnetization at room temperature are almost the same for both specimens, the coefficients at 4.2 K of Fe₇₂Pt₂₈ alloys is about one order smaller than that of Fe₆₅Ni₃₅ alloy. These results are coincident with those obtained by the recent measurements of the forced volume magnetostriction.     

High-field susceptibility and spin wave spectrum in FCC Fe-Ni alloys

The high-field susceptibility and spin wave spectra in fcc Fe-Ni alloys are calculated numerically in the coherent potential approximation by using the realistic band structures with t_2g and e_g symmetries and by taking into account the difference between the band-widths of fcc Fe and Ni.     

Characteristic x-ray temperature of Fe-Ni alloys with a distinct crystal lattice

The temperature dependence of the coefficient of thermal expansion (_t), therms dynamic displacements , and the characteristic x-ray Debye temperature (_x) of nickel-iron films (24–34% Ni, the rest Fe) with bcc and fcc lattices is studied.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, No. 5, pp. 52–56, May, 1978.     

Evidence for the correlation of the magnetic inhomogeneous structure with the fluctuation of chemical composition in Fe-Ni Invar alloys

Small-angle scattering of polarized neutrons from Fe₆₅⁶²Ni₃₅ Invar alloys was performed to demonstrate the correlation of the magnetic inhomogeneous structure with the fluctuation of the chemical composition. The result supports our previously proposed model in which the Ni-rich local regions tend to be ferromagnetic and the Fe-rich local regions paramagnetic.     

Solid state transformations in Fe-Ni alloys from meteorites in powder form

We report here Mössbauer studies by transmission and back-scattering technics, with Cape York and Santa Catharina meteorites in powder form. Martensitic transformation -phase to -phase is induced by mechanical treatment and long-range order is affected.     

Low-temperature electronic transport behaviour of powder-metallurgical SiGe alloys

Electronic transport properties of mechanically alloyed phosphorous-doped SiGe alloys at low temperatures were examined. We found that in this granular medium hopping-processes show an influence on the electronic conductivity. In addition, Hall-measurements revealed that the electron mobility reflects the band-structure of this alloy concerning intervalley-scattering and alloy-scattering. Mobility reaches a minimum at an alloy composition of roughly 25 at.% silicon.     

Mössbauer of γFe-Ni alloys

Mössbauer measurement performed as a function of temperature show quite different patterns for iron and nickel rich γ Fe-Ni alloys. Isotropic magnetic and additionally both anisotropic magnetic and electric contributions from neighbour atoms to the hyperfine interactions are considered. The temperature dependence of the isotopic contributions suggests the exchange integral J_FeFe to be not constant.     

X-ray “tails” on powder patterns of annealed Au-Pt and Fe-Ni alloys

The paper describes tails and side-bands observed on the diffraction patterns of samples after diffusion heating. The origin of tails is explained by the presence of vacancy clusters. Side-bands on X-ray patterns of an Au-Pt sample are interpreted in terms of a pre-precipitate structure or of a metastable phase in the region rich in gold.Thanks for valuable advice are due to RNDr. M. ernohorský CSc., whose suggestions gave rise to this paper.