Ferromagnetic Binary Alloys Research Articles

Magnetic States of a Binary Ferromagnetic Alloy with Competition of Easy‐Axis and Easy‐Plane Single‐Ion Anisotropies

AbstractThe magnetic phase diagrams of a binary ferromagnetic alloy with positive nearest‐neighbour exchange interactions and competing easy‐axis and easy‐plane single‐ion anisotropies are investigated in the molecular field approximation, especially the possibility of random asperomagnetic and fan states at low temperatures. The spontaneous magnetization vectors for these states are aligned along the crystallographic axes and the transverse projections of atomic spins are frozen in an incoherent spin‐glass like manner.

A binary ferromagnetic alloy with magnetic moments dependent on local environment. II. Neutron magnetic elastic scattering and hyperfine field distribution

AbstractThe neutron magnetic elastic scattering and the hyperfine field distribution are calculated for a collinear ferromagnetic alloy with magnetic moments which depend on their local chemical environment in a step‐like manner (Jaccarino‐Walker model). The question is analyzed how, using experimental data, one can discern the model under study from a binary magnetic alloy with competitive nearest‐neighbour exchange interactions and permanent magnetic moments. In the framework of the Jaccarino‐Walker model the concentration dependences of the spontaneous magnetization and Curie temperatures for Ni and Co alloys with elements of the Pt as well as Pd group are considered.

A binary ferromagnetic alloy with magnetic moments dependent on local environment. I. The Jaccarino‐Walker Model in the effective field approximation

AbstractA binary ferromagnetic alloy, in which the magnetic moments depend on their local chemical environment in a step‐like manner (the Jaccarino‐Walker model), is considered. It is assumed that Heisenberg exchange interactions of the nearest neighbours are responsible for the ferromagnetic ordering of these magnetic moments. Both, the Curie temperatures versus concentration and the percolation thresholds of the existence of the long‐range magnetic order are investigated for different variants of dependences of both the magnetic components on their local environments. The spin‐wave spectrum is analyzed as well.

Finite-Temperature Magnetism of Concentrated Ferromagnetic Alloys

A spin fluctuation theory developed previously by the present author using the functional integral method is generalized to discuss the finite-temperature properties of concentrated ferromagnetic binary alloys, A x B 1- x . We study the concentration- and temperature-dependences of various quantities such as the average magnetic moment, the local magnetic moment relevant to each constituent atom, the total spin susceptibility and partial susceptibilities of A and B atoms. It is shown that the theory in the limit of T =0 K reduces to that proposed by Hasegawa and Kanamori, and that the defect inherent in the one-electron theory of magnetic alloys is removed by including the effect of spin fluctuations. Numerical calculations are carried out for FeCr alloys.

Spin wave stiffness constant of narrow‐band ferromagnetic alloys with random hopping

AbstractThe spin wave stiffness constant D of ferromagnetic binary metallic alloys is derived at zero temperature from a random Hubbard model including diagonal and off‐diagonal disorder. The fluctuations of the hopping integrals are restricted to the additive limit. Vertex corrections to D due to the randoness of the transverse spin current are calculated in an extended CPA. D is renormalized by electron‐electron correlations within the coherent horizontal ladder approximation. Stability and damping of the spin waves, Ward relations, and the electrical conductivity are discussed.

Short-range and long-range ordering in ferromagnetic binary alloys

Atomic and magnetic ordering are described in a pair model. Some exact results are obtained for short-range correlation parameters in a one-dimensional alloy. Then, for the more realistic three-dimensional case, a generalised quasi-chemical approximation is introduced: long-range and short-range atomic and magnetic parameters are obtained as functions of temperature.

Annealed Ising Ferromagnet of Binary Alloys. II

Annealed Ising ferromagnetic Binary alloys of arbitrary concentrations are solved by use of the Takagi approximation. The atom ordering energy as well as the exchange energy are taken into account. In the present paper the case that one of the component atoms is non-magnetic is studied. Since the exchange energy and the atom ordering energy disturb each other, the onset of order tends to destroy the magnetization and vice versa. Therefore several critical concentrations are found. The complete phase diagram is obtained in which a tetra-critical point exists. Complicated calculations are carried out by the analytical method as much as possible and the rest is supplemented by the natural iteration method developed by Kikuchi using the computer.

A quasi-chemical model of strictly-regular ferromagnetic binary alloys containing a non-magnetic solute

A quasi-chemical theory of thermodynamics, based on a strictly-regular solution model, has been proposed for ferromagnetic binary alloys containing a non-magnetic solute. The free energies and the enthalpies of mixing as well as the effects of alloying on the Curie temperature and the spontaneous magnetization have been described in terms of the atomic interaction energy and the Heisenberg exchange integral. The theory has been shown to account fairly well for measured thermodynamic and ferromagnetic behaviors.

A note on magnon life-time in itinerant electron ferromagnetic alloys

A model of a binary ferromagnetic alloy A 1− c B c is discussed in terms of a single band Hubbard type hamiltonian. It is shown by summing up contribution of single-site scattering to all orders, that the inverse life time of long-wavelength magnons due to disorder scattering is proportional to q 5 and, in the limit c ⪡ 1, to the concentration c .

A Note on Orderings in Ferromagnetic Binary Alloys

A general formulation is given in treating an interrelationship between magnetic and atomic orderings in ferromagnetic binary alloys. The nature of the order parameter is re­ examined reflecting recent development in statistical mechanics. On the basis of the general formulation the usual molecular field approach to binary alloys is reconsidered. The critical slowing down is also discussed.

Annealed Ising Ferromagnet of Binary Alloys. I

Annealed Ising ferromagnetic Binary alloys of arbitrary concentrations are solved by use of the Takagi approximation. The atom ordering energy as well as the exchange energy are taken into account. In the present paper the case that one of the component atoms is non-magnetic is studied. Since the exchange energy and the atom ordering energy disturb each other, the onset of order tends to destroy the magnetization and vice versa. Therefore several critical concentrations are found. The complete phase diagram is obtained in which a tetra-critical point exists. Complicated calculations are carried out by the analytical method as much as possible and the rest is supplemented by the natural iteration method developed by Kikuchi using the computer.

The magnon stiffness constant in itinerant electron ferromagnetic alloys

A method of calculating the magnon energy in itinerant electron ferromagnetic binary alloys is developed. A model of a single narrow band determined by the Hubbard hamiltonian with substitutional impurities is considered. Calculations are based on an effective magnon hamiltonian, derived in RPA, and the magnon energy is determined from magnon Green function averaged over configurations.

Electron interactions and the spin‐wave stiffness constant in ferromagnetic two‐component alloys

AbstractElectron interaction effects and the spin‐wave stiffness constant of an ordered ferromagnetic binary alloy are studied. A general condition for ferromagnetism is obtained for the system. Within a certain approximation, an explicit expression for the spin‐wave stiffness constant is derived in the limit of very weak ferromagnetism.

A calculation of the electronic structure of an impurity atom of a non-transition element in ferromagnetic iron

The electronic structure of an impurity atom of a non-transition element (Al, Ga, Si, Ge and Sn) in ferromagnetic iron was calculated from first principles. The calculated change in the saturation magnetization due to an impurity atom, Delta m, is in good agreement with experimental data. Detailed discussions are given on the underlying mechanism of some systematic trends in the changes of Delta m with the kind of impurity atoms, and on different behaviour of Delta m in iron-based and nickel-based alloys. A qualitative interpretation is given to the observed Delta m in ferromagnetic binary alloys due to the addition of Al. Brief discussions are also given on the specific heat and on the soft X-ray emission spectra.

Effect of aluminium on the magnetic moments in ferromagnetic binary alloys

The effect of aluminium addition on the magnetic moments of the constituent atoms of binary BCC Fe-Co, Fe-Cr and FCC Ni-Fe alloys was investigated by comparing the results of Mossbauer and average magnetization measurements. It was found that the Al neighbours do not perturb the moment of Fe atoms in the Fe-Co and Ni-Fe alloys whereas there is a decrease in the Co and Ni moments. This different behaviour of Fe, Co and Ni towards the Al diluent is explained in terms of a simple local model. The simple model does not, however, explain the effects produced by Al in the BCC Fe-Cr alloys.

Relaxation Process of M-Induced Uniaxaial Magnetic Anisotropy

The kinetics of the relaxation process of the M-induced uniaxial magnetic anisotropy of the ferromagnetic binary alloy with the cubic structure was theoretically studied. The interaction energy of the closest pair of the X - and Y -atom is assumed to be written in the form of E XY = U XY + L XY (cos 2 α-(1/3)), where α is the angle between the bond direction of the atom pair and the direction of the magnetization. The first term is independent of α, and the second term is the pseudodipolar interaction term. The rate equation for the directional pair probability of the interacting atoms is obtained. According to this equation, the equilibrium value of the anisotropy energy is the same with Neel's formula, and the relaxation behavior of the anisotropy depends on the crystal structure.

Generalized CPA approach to the disordered Heisenberg ferromagnet

A ferromagnetic binary alloy is considered where each component has spin SA, SB and concentration XA, XB=1-XA, respectively. The interaction is given by the Heisenberg hamiltonian with exchange constants Jalpha beta between nearest-neighbour spins Salpha , Sbeta ( alpha , beta =A or B). It is shown that neglecting fluctuations in the static field seen by a spin SA (SB), generalized CPA equations can be written for the configurational average matrix Gij, with components Gijalpha beta . The formalism is symmetric in both components and valid for arbitrary values of the exchange constants and spins. In the general case it is expected to be good only for intermediate values of the concentrations, because it fails to reproduce the known exact results in the dilute limit Xalpha <<1( alpha =A or B) due to the approximate treatment of the local field that suppresses the p and d modes and modifies the energy of the s modes. However, it is shown that the theory reproduces the exact results when the values of the impurity and host spins are restricted by the condition (Salpha Jalpha alpha /Salpha Jalpha alpha )=1, where alpha =A or B if alpha =B or A.

Localization transitions for nuclear spin waves in ferromagnetic alloys

We investigate the possible localization of nuclear spin waves associated with the minority constituent of a binary ferromagnetic alloy. NMR methods for observing the transition and the time scale of propagating spin waves are suggested.

Spin-wave states and thermodynamics of ferromagnetic two-component alloys or compounds in the Heisenberg model

Abstract The dynamical and thermodynamical properties of a ferromagnetic binary alloy with two atoms per unit cell is studied in the Heisenberg model in order to find the effects of the optical branch on the thermodynamics and the correspondence between the spin-wave states in a simple metal (B non-magnetic or equal to A) and in alloy. The L12 structure is also studied and general conclusions have been drawn for the thermodynamical quantities.

Mn-Al強磁性合金の磁化の強さについて

The magnetic intensity of the π phase Mn-Al alloys of various compositions, with or without additional elements such as Ti, Cr, Fe, Co, Ni and Cu, has been measured. The decrease in Mn content and the addition of Ti element have been found to increase the magnetic intensity.The results of Mn-Al binary alloys can be explained in terms of the magnetic structure suggested by P. B. Braun, while those of the alloys with the additional elements can be explained by the magnetic structure with a modification (i.e. the alloy elements at the lattice positions which are estimated from the atomic volume as well as the electronegativity) and the empirical rule for magnetic moments of ferromagnetic binary alloys.