Reversible structural phase transition in Ni-Mn-Ga alloys in a magnetic field

In Ni_2+x Mn_1?x Ga shape-memory ferromagnetic alloys with coincident magnetic and structural phase transitions, a reversible structural field-induced phase transition was observed at constant temperature and pressure in magnetic fields of about 10 T. Computational results are in qualitative agreement with experiment.     

Possibility of a magnetic transition in Ce alloys

The fact that divalent rare earth impurities have a strong effect in lowering the α-γ transition temperature in Ce, allows the γ phase to become stable at low temperature without much change in its physical properties. The assumption that in this way an ordering (Néel) temperature can be reached, plus a thermodynamical analysis of the electronic transformation that takes place at the α-γ transition, leads to the prediction of a phase diagram for these alloys similar to that found in Cr doped V₂O₃.     

Determination of temperature of phase transition in magnetic alloys by branching theory methods

In this article a transcendental equation is obtained for the temperature T_c of the phase transition of a binary magnetic alloy by means of the cluster-variation method. The dependence of T_c on the exchange and crystallographic parameters, concentration, and coordination number is investigated. Particular cases are analyzed of a thinned and concentrated magnetic alloy. In the present article the cluster-variation method is employed to evaluate the dependence of concentration on the critical temperature of a magnetic binary alloy either with fixed or mobile atoms. A complete system of equations for the critical temperature can be obtained by using the branching theory [1]. When solving the equations, one finds that the equation which is written in terms of a determinant of a high order is the most difficult one. If one takes into account that the parameter of a near order depends on temperature (mobile atoms), then this increases the order of the determinant. The uses of symmetry enables one to lower considerably the order of the determinant in both cases,which makes it finally possible to solve the problem under consideration. The method yields qualitatively different results depending on whether the approximation is of fixed or mobile atoms (as previously noted, e.g., in [2]).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 107–112, May, 1978.     

Magnetovolume instability in FCC iron-nickel alloys

The possibility of magnetic and elastic instabilities is pointed out from the thermodynamic aspects of the magnetovolume properties of a ferromagnet, and the instabilities, Invar anomalies and martensitic transformations in fcc iron-nickel alloys are discussed.     

Electronic topological transitions and phase stability in the fcc Al-Zn alloys

We report on a detailed investigation of the phase equilibria and the Fermi surface in the Al-Zn system. Our calculation are based on the density functional theory and we use the linear muffin-tin orbital method and the Green's function technique. The calculated free energies of alloy formation exhibit the existence of a miscibility gap between the alloys containing approximately 10 and 55 at.% of Zn, in agreement with the phase diagram of the Al-Zn system. Seven electronic topological transitions (ETT) were found in Al-Zn system within the stability range of the fcc solid solution. A relation between these ETT and the phase stability of the fcc Al-Zn solid solutions is established. We show that extremum points on the concentration dependencies of the thermodynamic properties of Al-Zn alloys can be explained by band-filling effects. Received 6 February 2002 Published online 19 November 2002     

New Heusler alloys with a metamagnetostructural phase transition

Investigations of new ferromagnetic shape-memory Ni-Mn-Z Heusler alloys (Z = In, Sn, Sb) are reviewed. Experimental data are described and explained on the assumption that these alloys undergo a phase transition from the ferromagnetic to the antiferromagnetic state (metamagnetic transition). The results of theoretical studies of the phase diagrams of these alloys are considered with regard to the possible change in the character of magnetic ordering (from ferromagnetic to antiferromagnetic) and interaction of the structural martensitic transformation with the metamagnetic transition.     

Magnetic properties of electrodeposited iron-nickel alloys

The basic magnetic properties, viz., magnetic saturation and coercive force, have been established by measurement of about 150 specimens for electrodeposited iron-nickel alloys over the entire range of chemical compositions. The magnetization data were related ot the physicochemical aspects of the electrodeposition process.     

First order magnetic transition in doped CeFe2 alloys: phase coexistence and metastability

First order ferromagnetic (FM) to antiferromagnetic (AFM) phase transition in doped CeFe2 alloys is studied with the micro-Hall probe technique. Clear visual evidence of magnetic phase coexistence on micrometer scales and the evolution of this phase coexistence as a function of temperature, magnetic field, and time across the first order FM-AFM transition is presented. Such phase coexistence and metastability arise as a natural consequence of an intrinsic disorder-influenced first order transition. The generality of these phenomena involving other classes of materials is discussed.     

Some transport properties in martensitic iron-nickel alloys

Summary Resistivity, Hall effect and magnetoresistivity measurements in Fe−Ni alloy specimens with Ni content ranging from 29 to 32 wt.% and subjected to martensitic transformation have been performed. The results have been interpreted by considering both the mechanisms of the martensitic transformation, different in 29 and 30 wt.% Ni alloys from that in 31 and 32 wt.% Ni ones, and the theories of Smith and Berger on the Hall effect in dilute ferromagnetic alloys, which have been applied to the above-described alloys. The Hall data, analysed by means of Kohler polts, have allowed us to identify the charge carrier scattering mechanisms prevailing in the different alloys,i.e. the skew scattering in 29 and 30 wt.% Ni alloys and the side jump scattering in 31 and 32 wt.% Ni ones. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Hyperfine field distribution in electrodeposited iron-nickel alloys

The distribution of hyperfine fields in f.c.c. electrodeposited iron-nickel alloys with composition ranging from 10 to 27 at% Fe has been studied from the observed Mössbauer spectra using a method of analysis developed by Hesse and Rübartsch. The different I_2,5/I_1,6 values for the different parts of the same component sample indicate that the distribution of the electrical field in bath plays an important role in the spin preferred orientation within electrodeposited layer. The asymmetry in the width of Mössbauer lines has been discussed.     

The theory of atomic and magnetic ordering in ternary alloys with fcc lattice

We consider the theory of the mutual influence of atomic and spin ordering phenomena in ternary alloys of transition elements with fcc lattice. The case of quasibinary alloys B₃A-B₃D is considered in detail. Concentration dependences of the critical temperature of the order-disorder phase transition are considered for cases of atomic and magnetic ordering.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 48–57, December, 1970.     

Order-to-order phase transition in alloys with face-centered superstructures

The possibility of a temperature phase transition from one superstructure in a binary alloy to a superstructure of another type is theoretically considered. A possible phase diagram for these transitions is constructed.Translated from Izvestiya Vysshikh Uchebnykh. Zavedenii, Fizika, No. 8, pp. 26–30, August, 1982.     

Noncollinear magnetic structures in binary alloys of transition elements

Concepts [1–4] are developed on these structures for A–B alloys having antiferromagnetic interaction between the individual local magnetic moments . The following cases are considered: 1) the exchange integrals I_AA > 0, I_BB < 0, I_AB > 0, while _A and _B are dependent on the composition; 2) I_AA > 0, I_BB < 0, I_AB < 0; _A, _B = const. Models are used to calculate the mean atomic magnetic moment for Co-Cr, Co-Mn, and Ni-Cr alloys. The agreement with experiment is satisfactory.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, Vol.12, No. 1, pp. 96–102, January, 1969.     

Theory of volume anomalies in magnetic transition metal alloys

The electronic contribution to the pressures which determines the equilibrium volume of transition metals is parametrized by use of the interacting Anderson model. It is discussed that there are two mechanisms which can explain the volume anomalies in the Invar alloys. The Fe-Fe atomic interaction which seems to be important in the Invar effect is also discussed.     

On the dissymmetry of mossbauer spectra in iron-nickel alloys

Valuable information about the disappearance of magnetism in the invar region (concentration of 30–45 pct of nickel) may be obtained by the examination of Mössbauer spectra.^I–5 However, it appears that some characteristics of these spectra are already present in non invar spectra have not been taken in account up to now: even in a 50 pct alloy, the six lines have anomalous widths and heights, and it is the aim of this note to put a quantitative interpretation of this fact, letting for the future the extension to invar spectra.     

Enhancement of solute self-diffusion in fcc alloys

Using a new simulation approach to the calculation of correlation factors in very dilute solutions, the present paper reports on results of the first calculations of the first and second solute enhancement factors for solute self-diffusion in the fourteen-frequency model postulated by Bocquet for describing the diffusion kinetics of paired and unpaired solute atoms in dilute fcc alloys. Bocquet's assumption that correlation effects do not contribute to solute self-diffusion enhancement is shown to have a fairly limited range of validity. Specifically, it is shown that this assumption is reasonable when the solvent–vacancy exchange frequency far from the solute is high compared with the others or when all of the solute–vacancy exchange frequencies are small compared with the others. The assumption is also reasonable when the vacancy is not attracted to the solute atoms and when the vacancy does not often alternate between two solute atoms. The present study would strongly suggest that many of the ratios of exchange frequencies that have been determined from experimental data on the basis of this assumption are likely to be in error.