Ferromagnetic Binary Alloys Research Articles

Spin-mediated charge-to-heat current conversion phenomena in ferromagnetic binary alloys

Spin-mediated charge-to-heat current conversion phenomena, i.e., the anomalous Ettingshausen effect (AEE) and the anisotropic magneto-Peltier effect (AMPE), have been investigated in various ferromagnetic Ni-Fe, Ni-Pt, Ni-Pd, and Fe-Pt binary alloys at room temperature. When a charge current is applied to a ferromagnetic conductor, the AMPE modulates the Peltier coefficient depending on the angle between the directions of the charge current and magnetization, while the AEE generates a heat current in the direction perpendicular to both the charge current and magnetization. We observed the strong material dependence of the thermoelectric conversion coefficients and figures of merit of these phenomena. Among the ferromagnetic alloys used in this study, Ni$_{95}$Pt$_{5}$ exhibits the largest AMPE of which the anisotropy of the Peltier coefficient is $\sim 12\%$. In contrast, the magnitude of the AEE signals is moderate in Ni$_{95}$Pt$_{5}$ but largest in Ni$_{75}$Pt$_{25}$ and Ni$_{50}$Fe$_{50}$. We discuss these behaviors by exploring the relations between these charge-to-heat current conversion phenomena and other transport as well as magnetic properties. This systematic study will provide a clue for clarifying the mechanisms of the AMPE and AEE and for enhancing the thermoelectric conversion efficiency of these phenomena.

Predicting magnetization of ferromagnetic binary Fe alloys from chemical short range order

Among the ferromagnetic binary alloys, body centered cubic (bcc) Fe-Co is the one showing the highest magnetization. It is known experimentally that ordered Fe-Co structures show a larger magnetization than the random solid solutions with the same Co content. In this work, based on density functional theory (DFT) studies, we aim at a quantitative prediction of this feature, and point out the role of the orbital magnetic moments. Then, we introduce a DFT-based analytical model correlating local magnetic moments and chemical compositions for Co concentrations ranging from 0 to 70 at.%. It is also extended to predict the global magnetization of both ordered and disordered structures at given concentration and chemical short range orders. The latter model is particularly useful for interpreting experimental data. Based on these models, we note that the local magnetic moment of a Fe atom is mainly dictated by the Co concentration in its first two neighbor shells. The detailed local arrangement of the Co atoms has a minor effect. These simple models can fully reproduce the difference in magnetization between the ordered and disordered Fe-Co alloys between 30% and 70% Co, in good agreement with experimental data. Finally, we show that a similar model can be established for another bcc binary Fe alloy, the Fe-Ni, also presenting ferromagnetic interactions between atoms.

Tunning exchange bias in inverted antiferromagnetic/ferromagnetic core/shell nanoparticles by binary alloy shells

A detailed investigation of exchange bias properties of an inverted nanoparticle with an antiferromagnetic core and a ferromagnetic binary alloy shell of the type BxC1−x is presented by benefiting from Monte Carlo simulations. Exchange bias displays a non-monotonic behavior with the varying value of the concentration the type-B magnetic components, x. Coercivity exhibits a monotonic or a non-monotonic variation with x depending on the relative strength between unlike magnetic components in the shell. Particular attention has also been given to determine the effects of the cooling field process on the magnetic properties of the nanoparticle. Numerical results obtained in this work present a different physical mechanism and an alternative way for tuning the exchange bias and coercivity of bimagnetic core/shell nanoparticles.

Non-equilibrium phase transition properties of disordered binary ferromagnetic alloy

Non-equilibrium dynamic phase transition features of a disordered binary ferromagnetic alloy consisting of spin-1/2 and spin-1 components under the presence of a time dependent oscillating magnetic field have been analyzed for a two dimensional square lattice. With the help of Glauber-type stochastic process, the kinetic equations of time dependent magnetizations have been derived based on the effective-field theory with single-site correlations. A systematic analysis for the whole range of the concentrations of randomly distributed components as well as other system parameters has been carried out. According to our numerical investigations, the considered system presents unusual thermal and magnetic field behaviors such as the existence of dynamic multi-critical behavior and also boundaries of the coexistence region, where both dynamically ordered and disordered phases overlap, sensitively depends on the studied parameter space.

Magnetic response of a disordered binary ferromagnetic alloy to an oscillating magnetic field

By means of Monte Carlo simulation with local spin update Metropolis algorithm, we have elucidated non-equilibrium phase transition properties and stationary-state treatment of a disordered binary ferromagnetic alloy of the type ApB1−p on a square lattice. After a detailed analysis, we have found that the system shows many interesting and unusual thermal and magnetic behaviors, for instance, the locations of dynamic phase transition points change significantly depending upon amplitude and period of the external magnetic field as well as upon the active concentration of A-type components. Much effort has also been dedicated to clarify the hysteresis tools, such as coercivity, dynamic loop area as well as dynamic correlations between time dependent magnetizations and external time dependent applied field as a functions of period and amplitude of field as well as active concentration of A-type components, and outstanding physical findings have been reported in order to better understand the dynamic process underlying present system.

Effect of chemical ordering on 90° interlayer coupling in epitaxial Co–Fe/Cr/Co–Fe thin films

Interlayer exchange coupling (IEC) was studied in ferromagnetic binary alloy Co–Fe thin films through Cr spacer to investigate systematically, the effects of chemical compositions and the chemical ordering on the observation of 90° interlayer coupling in magnetic alloy based structures. The dominating 180° coupling with weak 90° coupling was observed at room temperature deposited CoxFe1−x/Cr/CoxFe1−x (x=0 to 0.8) trilayer samples for all values of x. However, the strength of the 90° coupling for x=0.4 and 0.5 was found to increase with increasing the annealing temperature, Tann for the bottom CoxFe1−x layer and the strength of 90° coupling became comparable to that of 180° coupling at Tann=400°C. The enhancement of 90° coupling was considered to be originated from the unconventional interfacial magnetic exchange interactions between Cr and Co (and Fe) due to the appearance of antiphase structures at the interface with the enhancement of chemical ordering (B2 ordering) which was confirmed by synchrotron X-ray diffraction.

X-Ray Magnetic Diffraction Experiment of Fe<sub>3</sub>Pt Alloy in Order Phase

We have performed X-ray magnetic diffraction experiments of a ferromagnetic binary alloy Fe3Pt in order phase, and have measured separately spin and orbital magnetic form factors. By a curve-fitting analysis in which atomic-model form factors of Fe-3d and Pt-5d electrons under the dipole approximation are assumed, we have obtained the spin and orbital magnetic moments of Fe and Pt atoms separately. The present result is comparable to those of other experimental and theoretical studies, which shows the validity of this experimental method.

Thermal artifact on the spin Seebeck effect in metallic thin films deposited on MgO substrates

Spin Seebeck effect (SSE) was investigated in Heusler compound Co2MnSi (CMS) and ferromagnetic binary alloy Ni80Fe20 (Py) thin films deposited on MgO substrates at different ambient temperatures, T = 30 K to 295 K, by maintaining a finite temperature gradient along the film plane. Low temperature enhancement of voltage signal and a peak around T = 70 K were detected in a Pt wire placed on the higher temperature end of CMS (or Py) film. It has been found that the low temperature enhancement was dominated by a thermal artifact, which was generated by the anomalous Nernst effect with an additional perpendicular temperature gradient across the film plane. The remarkable mismatch between thermal conductivities of MgO and CMS (or Py) at low temperatures is considered to give rise to the perpendicular temperature gradient causing the thermal artifact. We showed that consideration of thermal conductivity matching between thin film and substrate is essential for performing experiments of SSE correctly; moreover, the observation of SSE could be realized only when minimization of the thermal artifact is possible.

Lattice dynamics and structural stability of orderedFe3Ni,Fe3PdandFe3Ptalloys using density functional theory

We investigate the binding surface along the Bain path and phonon dispersion relations for the cubic phase of the ferromagnetic binary alloys Fe3X (X = Ni, Pd, Pt) for L12 and DO22 ordered phases from first principles by means of density functional theory. The phonon dispersion relations exhibit a softening of the transverse acoustic mode at the M-point in the L12-phase in accordance with experiments for ordered Fe3Pt. This instability can be associated with a rotational movement of the Fe-atoms around the Ni-group element in the neighboring layers and is accompanied by an extensive reconstruction of the Fermi surface. In addition, we find an incomplete softening in [111] direction which is strongest for Fe3 Ni. We conclude that besides the valence electron density also the specific Fe-content and the masses of the alloying partners should be considered as parameters for the design of Fe-based functional magnetic materials.

Preparation of ferromagnetic binary alloy fine fibers by organic gel-thermal reduction process

Ferromagnetic metal fibers with a high aspect ratio (length/diameter) are attractive for use as high performance electromagnetic interference shielding materials. Ferromagnetic binary alloy fine fibers of iron-nickel, iron-cobalt and cobalt-nickel were prepared by the organic gel-thermal reduction process from the raw materials of critic acid and metal salts. These alloy fibers synthesized were featured with a diameter of about 1 um and a length as long as 1 m. The structure, thermal decomposition process and morphologies of the gel precursors and fibers derived from thermal reduction of the gel precursors were characterized by FTIR, XRD, TG/DSC and SEM. The gel spinnability largely depends on the molecular structure of metal-carboxylates formed during the gel formation. The gel consisting of linear-type structural molecules shows good spinnability.

An application of the dynamical mean-field approximation to ferromagnetic alloys

The effect of the fluctuation of local correlation in the phase diagram of binary ferromagnetic alloy is investigated by using the coherent potential approximation and the dynamical mean field approximation. The Curie temperature varies smoothly as the function of the concentration. This behaviour is different from the phase diagram which is calculated by the Hartree–Fock approximation.

Spin Density in Real and Momentum Space in Multi-Atom Alloys by KKR-CPA Method

The application of the spin-polarized version of multiple scattering the- ory for obtaining electron charge and spin densities in both real and momen- tum spaces of concentrated, multi-atom disordered alloys is presented. This method is based on the Korringa—Kohn—Rostoker (KKR) band structure ap- proach and coherent potential approximation (CPA) method. The effective one-electron potential is constructed within local spin density approxima- tion. The magnetic neutron form factors are in real space of our main inter- est. With the recent developments of new synchrotron photon sources, the Compton profile becomes the most interesting target in momentum space. In the most of examples, spin momentum density and its specific structure due � to Fermi surface will be shown. To get accurate enough description in mo- mentum space and quantity like Compton profile, the determination of the Fermi surface must be done with high precision. In this context we show how to apply generalized Lloyd formula for accurate determination of the Fermi level. Also we show how to use efficiently complex energy integration method for the computation of matrix elements, G(τ, τ) or G(p, p), of the KKR—CPA Green . function. Results for the iron—silicon ferromagnetic binary alloys and half-metallic ferromagnetic Heusler alloys are presented. PACS numbers: 71.15.Cr, 71.18.+y, 78.90.+t

Effect of disorder on the critical behaviour of a ferromagnetic binary Ising alloy

The effect of site and exchange disorders on the critical behaviour of a disordered ferromagnetic Ising binary alloy is studied by evaluating the magnetization and the susceptibility with the help of a cluster-variational method. The critical exponents γ ∗ and γ describing, respectively, the linear and nonlinear scaling of the susceptibility exhibit a non-monotonic temperature dependence for T> T c.γ ∗ increases with increasing disorder. The critical exponent β increases with disorder, whereas δ remains unaffected. A rapid shrinking of the asymptotic critical region and variation of the limiting ( T>> T c) values of γ = Θ p / T c with the increase in disorder are observed.

ChemInform Abstract: Magnetic Diffuse Scattering

The diffuse scattering of neutrons from magnetic materials provides unique and important information regarding the spatial correlations of the atoms and the spins. Such measurements have been extensively applied to magnetically ordered systems, such as the ferromagnetic binary alloys, for which the observed correlations describe the magnetic moment fluctuations associated with local environment effects. With the advent of polarization analysis, these techniques are increasingly being applied to study disordered paramagnetic systems such as the spin-glasses and the diluted magnetic semiconductors. The spin-pair correlations obtained are essential in understanding the exchange interactions of such systems. In this paper, we describe recent neutron diffuse scattering results on the atom-pair and spin-pair correlations in some of these disordered magnetic systems. 56 refs.

Isotope Effects in the Diffusion of Hydrogen and Deuterium in Ferromagnetic Binary Alloys of the Cu3Au Type*

Article Isotope Effects in the Diffusion of Hydrogen and Deuterium in Ferromagnetic Binary Alloys of the Cu3Au Type* was published on January 1, 1989 in the journal Zeitschrift für Physikalische Chemie (volume 164, issue 1).

Electric hyperfine interactions in ferromagnetic binary alloys above the curie temperature

In the frame of an unscreened point charge model we calculated all possible electric field gradients for first neighbor atom arrangements in disordered binary fcc alloys. With these values and a distribution of isomer shifts we fit experimental spectra of nearly disordered alloys.

Magnetic Diffuse Scattering

The diffuse scattering of neutrons from magnetic materials provides unique and important information regarding the spatial correlations of the atoms and the spins. Such measurements have been extensively applied to magnetically ordered systems, such as the ferromagnetic binary alloys, for which the observed correlations describe the magnetic moment fluctuations associated with local environment effects. With the advent of polarization analysis, these techniques are increasingly being applied to study disordered paramagnetic systems such as the spin-glasses and the diluted magnetic semiconductors. The spin-pair correlations obtained are essential in understanding the exchange interactions of such systems. In this paper, we describe recent neutron diffuse scattering results on the atom-pair and spin-pair correlations in some of these disordered magnetic systems. 56 refs.

Preparation and Characteristics of Co-Cr Films by EP Magnetron Co-sputtering Technique

Experimental results are given on high-rate low-temperature deposition of Co-Cr films using an exposed pole (EP) magnetron simultaneous sputtering system developed by the authors for deposition of ferromagnetic binary alloy films. A composite target is prepared consisting of a Co washer, a Cr cylinder, and a Co disk; the performance of the sputtering system is examined and the film quality evaluated. The results are as follows: 1) the maximum deposition rate was as high as 0.18 μm/min for 7.6 W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of input power; 2) the deposition rate was higher for lower sputtering gas pressures; 3) the substrate temperature was as low as 100°C for 7.6 W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> input power; 4) the C-axis of the deposited Co-Cr films was oriented perpendicular to the film plane, with Δθ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> = 8 to 13°; and 5) perpendicular magnetic anisotropy films were obtained when the film M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> = 300 to 800 emu/cc and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> = 250 to 350 Oe. Thus it is concluded that EP magnetron simultaneous sputtering is very useful for the deposition of Co-Cr films.

ＥＰマグネトロンスパッタ法によるＣｏ‐Ｃｒ膜の作成と特性

This paper is concerned with the experimental results of the high rate and low temperature deposition of Co-Cr films using an exposed pole (EP) magnetron co-sputtering system developed by the authors for deposition of ferromagnetic binary alloy films. In this paper we prepare a composite target constructed of a Co washer, a Cr cylinder and a Co disk, and examine the performance of the sputtering system and evaluate the film quality. Results : 1) Maximum deposition rate was as high as 0.18 μm/min for 7.6 W/cm2 input power. 2) The deposition rate was higher for lower sputtered gas pressure. 3) The substrate temperature was as low as 100°C for 7.6 W/cm2 input power. 4) The C-axis of the deposited Co-Cr films were in the perpendicular direction to the film plane and Δθ50=8-13°.5) Perpendicular magnetic anisotropy films were obtained for the films of Ms=300-800 emu/cc and Hc=250-350 Oe. Thus, it is concluded that EP magnetron co-sputtering is very effective for the deposition of Co-Cr films.

Ferromagnetism and spatial long-range order in binary alloys. II. Systems with face-centred cubic structure

For part I, see ibid., vol.13, p.1715 (1980). A mean-field theory of order-disorder transformations in ferromagnetic binary alloys with face-centred cubic structure is presented. The effect of magnetism in the spatial first-order phase transformation is studied in detail. Results for the temperature dependence of the order parameters for the phase diagram and for the concentration dependence of the discontinuity in the spatial long-range order parameter at the transition temperature are shown.