Influence of atomic ordering on the magnetic properties of FePd,FePt, and Fe<Subscript>50</Subscript>Pd<Subscript>50−<Emphasis Type="Italic">x</Emphasis></Subscript>Pt<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> alloy films

The phase composition, crystal structure, and magnetic properties of films of the ordered alloys FePd, FePt, and Fe₅₀Pd_{50 − x} Pt _x , where x = 1–10 at %, were analyzed. The spectral dependences of the magnetic rotation and optical absorption were taken. The effect of heat treatment on the crystal structure, magnetization, and coercive field strength of the ordered alloy films was studied. The influence of the degree of atomic ordering on the perpendicular magnetic anisotropy was investigated. It was shown that films of ordered FePd and FePt alloys of equiatomic composition and films of Fe₅₀Pd_{50 − x} Pt _x , where x = 1–10 at %, can serve as media for magnetic and thermomagnetic data recording and storage.     

Perpendicular magnetic anisotropy in the Co50Pt50, Co50Pd50, and Co50Pt50 ? xPdx thin films

Films of the Co₅₀Pt₅₀, Co₅₀Pd₅₀, and Co₅₀Pt_{50 − x} Pd _x alloys (where x = 1–10 at %) have been prepared. The processes of atomic ordering and its influence on the perpendicular magnetic anisotropy and the coercive force in these films have been investigated. The dependence of the coercive force on the film thickness has been analyzed. It has been shown that thin films of ordered alloys become magnetically uniaxial with the easy axis normal to their plane and can be used for magnetic and thermomagnetic recording and storage of information.     

Possible reconstruction of the ferromagnetic state under the influence of superconductivity in epitaxial V/Pd1−x Fe x bilayers

Epitaxial V/Pd_1−x Fe _x (001) bilayers with a V thickness of the order of 40 nm and with a Pd_1−x Fe _x thickness in the range from 0.8 nm to 4.4 nm were prepared by molecular beam epitaxy techniques. The Curie temperature of the Pd_1−x Fe _x layers varies between 90 and 250 K. For a bilayer with a Pd_1−x Fe _x thickness of 1.2 nm the ferromagnetic resonance measurements revealed a decrease of the effective magnetization 4πM _eff of the ferromagnetic layer below the superconducting transition temperature of V. As a possible explanation for this decrease we suggest a spatial modulation of the ferromagnetic order in the Pd_1−x Fe _x layer due to modifications of the indirect exchange interaction of magnetic ions via conduction electrons in the superconducting state. A comparison with a recent theoretical investigation supports this possibility.     

Perpendicular magnetic anisotropy in Co50Pt50 and Co50Pt50 ? x Pd x films

Atomic ordering and its effect on the perpendicular magnetic anisotropy and coercive force in Co₅₀Pt₅₀ and Co₅₀Pt_{50 − x} Pd _x (x = 3–10 at %) alloy films are investigated. The dependence of the coercive force on the film thickness is studied. It is shown that thin films of the ordered alloys become magnetically uniaxial with the easy magnetic axis normal to the plane of the film. Such films can be used for magnetic and thermomagnetic data recording and storage.     

Magnetic properties of small amounts of iron dissolved in copper palladium alloys

The magnetic susceptibilities of copper-rich Cu_1−x Pd _x Fe _y alloys,x=0−0.40,y=30−300 ppm, have been measured in the temperature range 1.7 K–300 K. The results imply that an iron atom induces a magnetic moment of about 0.35μ _B on a nearest neighbour palladium atom. Conversely the effect of the nearest neighbour palladium atom on the iron atom itself leads to a stabilization of the iron moment indicated by a lowering of its Kondo temperature.     

Studies on the valence electronic structure of Fe and Ni in Fe x Ni1−x alloys

K _β-to-K _α X-ray intensity ratios of Fe and Ni in pure metals and in Fe _x Ni_1−x alloys (x=0.20, 0.50, 0.58) exhibiting similar crystalline structure have been measured following excitation by 59.54 keV γ-rays from a ²⁴¹Am point source, to understand as to why the properties of permalloy Fe_0.2Ni_0.8 is distinct from other alloy compositions. It is observed that the valence electronic structure of Fe_0.2Ni_0.8 alloy is totally different from other alloys which may be attributed to its special magnetic properties.     

Hyperfine magnetic fields in Fe−Co alloys and their tempera ture dependences

We obtained⁵⁷Fe hyperfine field parameters from Fe₁−x-Co _x alloys (0≤x≤0.6) from 77 K to 900 K. We first discuss the origin of the low temperature hyperfine fields in terms of the 3d and 4s electrons at⁵⁷Fe atoms. The⁵⁷Fe hyperfine magnetic field (hmf) of Fe-Co alloys depends more weakly on temperature than the hmf of pure Fe. This temperature dependence occurs because the alignment of the magnetic moments at both the Fe atoms and at the Co atoms depend on temperature in the same way as the bulk magnetization of Fe-Co alloys.     

Microstructure and magnetic properties in arrays of ac electrodeposited FexNi1?x nanowires induced by the continuous and pulse electrodeposition

FeNi nanowires were fabricated by ac and pulse electrodeposition into the alumina template matrix. The effects of continuous ac electrodeposition as well as pulse features on the structure and magnetic properties of the nanowire arrays were studied. The microstructures and magnetic properties of the Fe _x Ni_1−x nanowires are seen to be independent of the deposition frequency and off-time between the pulses. The ac electrodeposited Ni nanowires were not formed at more than 400  Hz deposition frequency, while the Fe _x Ni_1−x nanowires, containing a small amount of Fe, formed in the all frequencies. For x less than 50% the coercivity slowly increases but over 50% Fe added to the FeNi alloy increases the coercivity with a higher rate and maximum coercivity was seen for the Fe_0.97Ni_0.03. The Fe and Fe _x Ni_1−x nanowires containing less than 30 at.% Ni was seen to have a bcc structures with (110) preferential direction while Fe _x Ni_1−x nanowires with more than 30 at.% Ni showed (110) bcc (Fe) and/or (111) bcc (FeNi) plus (111) fcc (Ni). A preferential (111) fcc structure was obtained for the Ni nanowires.     

Transport properties of antiferromagnetic fcc-iron alloys

A study is reported of the electrical resistance and thermopower of Fe_xNi_80−x Cr₂₀ fcc alloys within the 44⩽x⩽70 at. % range. It is shown that, at low temperatures, they typically exhibit minima in the temperature dependences of electrical resistance. The appearance of these anomalies is attributed to the formation of a gap in the conduction electron spectrum due to the onset of long-or short-range antiferromagnetic order in the alloys. The effect of magnetic field on the magnetic states appearing in frustrated antiferromagnetic alloys has been studied, and an H-T magnetic phase diagram constructed. Fiz. Tverd. Tela (St. Petersburg) 40, 101–105 (January 1998)     

Hyperfine field relaxations in the Fe−Co−B amorphous alloys

A systematic increase of the average hyperfine magnetic induction at⁵⁷Fe measured at room temperature during interrupted isothermal annealing was found to be inherent to the irreversible relaxation processes in the Fe−B based soft magnetic alloys at moderately elevated temperatures. Assuming superimposed asymptotic exponential field vs. time dependences. several processes can be distinguished, their relaxation times determined and from the Arrhenius-like log τ vs. 1/T plots average activation enthalpies estimated. Results on the Fe₇₀Co₁₀B₂₀ and Fe_85−x Co _x B₁₅ (x=17, 19 and 21 at. % Co) amorphous ribbons between 100 and 200°C are compared and discussed in terms of possible stress relief, free volume annihilation and short range ordering mechanisms.     

Influence of nickel on iron-deficient spinel ferrites

A detailed study of the electric and magnetic properties of ceramic nickel-ferrites, Ni _x Fe_3−x−ΔO₄ withX≧0.8 and Δ≦10⁻² is presented. The physical interpretation of the results, the x-ray structural analysis and the magnetic aftereffects spectra allow us to define the substitution mechanism Ni↔Fe and explain the progressive variation of the properties in the samples with increasing concentrations of nickel.     

Mössbauer study of mechanosynthesized iron carbides

Syntheses of Fe_1−x C _x alloys (forx≲0.15) and carbides (for 0.15≲x≲0.50) can be obtained by room temperature grinding of the elemental Fe and C powders. The formation of cementite is completed after about 20 h, whereas the alloys are synthesized in critical processing conditions. Synthesized cementite has a high density of defects and particle size down to 10 nm.     

Morphology and magnetic properties of Fe x Co1−x /Co y Fe3−y O4 nanocomposites prepared by surfactants-assisted-hydrothermal process

Recently, we have demonstrated the successful synthesis of Fe _x Co_1−x /Co _y Fe_3−y O₄ nanocomposites with various alkaline solutions by using surfactants-assisted-hydrothermal (SAH) process. In this article, the synthesis of Fe _x Co_1−x /Co_yFe_3−y O₄ nanocomposites with their sizes varying between 20 nm and 2 μm was reported. X-ray powder diffraction (XRD) analyses showed that the surfactants, pH, precipitator, and temperature of the system play important roles in the nucleation and growth processes. The magnetic properties tested by vibrating sample magnetometer (VSM) at room temperature exhibit ferromagnetic behavior of the nanocomposites. These Fe _x Co_1−x /Co _y Fe_3−y O₄ nanocomposites may have a potential application as magnetic carriers for drug targeting because of their excellent soft-magnetic properties.     

Structure, spin reorientation and M?ssbauer effect studies of Tb0.3Dy0.7(Fe1?xAlx)1.95 alloys

The effect of Al substitution for Fe on crystal structure, magnetostriction and spontaneous magnetostriction, anisotropy and spin reorientation of a series of polycrystalline Tb_0.3Dy_0.7(Fe_1−x Al_x)_1.95 alloys (x = 0, 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, 0.35) at room temperature and 77 K was investigated systematically. It was found that the primary phase of Tb_0.3Dy_0.7(Fe_1−x Al_x)_1.95 is the MgCu₂-type cubic Laves phase structure when x < 0.4 and the lattice constant a of Tb_0.3Dy_0.7(Fe_1−x Al_x)_1.95 increases approximately and monotonically with the increase of x. The substitution of Al leads to the fact that the magnetostriction λ inceases slightly in a low magnetic field (H ⩽ 40 kA/m), but decreases sharply and is easily close to saturation in a high applied field as x increases, showing that a small amount of Al substitution is beneficial to a decrease in the magnetocrystalline anisotropy. It was also found that the spontaneous magnetostriction λ ₁₁₁ decreases greatly with x increasing. The analysis of the M?ssbauer spectra indicated that the easy magnetization direction in the {110} plane deviates slightly from the main axis of symmetry with the changes of composition and temperature, namely spin reorientation. A small amount of non-magnetic phase exists for x = 0.15 in Tb_0.3Dy_0.7(Fe_1−x Al_x)_1.95 alloys and the alloys become paramagnetic for x > 0.15 at room temperature, but at 77 K the alloys still remain magnetic phase even for x = 0.2. At room temperature and 77 K, the hyperfine field decreases and the isomer shifts increase with Al concentration increasing.     

Magnetic properties of metallic glasses of the type Fe80−x Pd x B20 and Fe80−x Pt x B20

Amorphous alloys of the type Fe_80???xPd_xB₂₀ and type Fe_80???xPt_xB₂₀ for 0?≤?x?≤?50 have been investigated by means of ⁵⁷Fe Mössbauer spectroscopy and magnetisation measurements in temperatures from 4.2 up to 300 K. Curie temperatures and crystallisation temperatures are found by DTMG-DTA method. Mössbauer spectroscopy magnetic field is observed to visible increase for x?=?1 and 1.5% at room temperature for Pd, while a decrease is observed for higher x values. Curie temperature for Pd alloys has a maximum at x?=?4 with T _C?=?753 K, which supports enforcing influence of Pd at low concentrations of Pd for magnetic interactions. We discuss different explanations for these measurements and compare with other findings for high Pd concentrations and alloys with Pt instead of Pd.     

Effect on the magnetic properties of small substitutions of iron and copper for nickel in YNi3 and Y2Ni7 intermetallics

Measurements of magnetization in static fields up to 60 kOe and magnetic susceptibility in weak ac fields of the Y(Ni_1−x M_x)₃ and Y₂(Ni_1−x M_x)₇ intermetallics (M=Fe and Cu, x _max=0.2), as well of the specific heat of these systems for some compositions are reported. It was found that these intermetallics are ferromagnetic at low temperature, and that their spontaneous magnetizations M _s at 4.2 K and Curie temperatures T _C decrease monotonically with increasing copper concentration. The magnetic susceptibility of the Y(Ni_1−x Fe_x)₃ system with 0.06≲x≲0.2 was observed to decrease rapidly with the temperature lowered below a characteristic temperature T _s. One of possible reasons for such an anomaly is shown to be the onset in this concentration region of the reentrant spin-glass state at low temperatures. The results obtained demonstrate that the tight-binding d-band model fails to explain the evolution of the magnetic properties of YNi₃ and Y₂Ni₇ in the case of small substitutions of iron and copper for nickel. Fiz. Tverd. Tela (St. Petersburg) 39, 1828–1830 (October 1997)     

Effect of severe plastic deformation on the properties of the Pt<Subscript>3</Subscript>Fe antiferromagnet

The effect of atomic disordering on the magnetic, electrical, and optical properties of the Pt_74.1Fe_25.9alloy close in composition to the stoichiometric Pt₃Fe alloy has been studied. It has been shown that, as a result of severe plastic torsional deformation under high pressure, the alloy transforms from the antiferromagnetic state (T _N=164 K) into the ferromagnetic state (T _C≈400 K). In this case, the residual electrical resistivity increases by a factor of more than two and the thermopower changes its sign from positive to negative. The results of the studies of the optical conductivity agree with the previously calculated electronic spectra of the atomically ordered and disordered Pt₃Fe alloys in the range of interband transitions and with the obtained data on the electrical properties in the infrared range.     

Ferromagnetic resonance and magnetic microstructure in nanocomposite films of Cox(SiO2)1 ? x and (CoFeB)x(SiO2)1 ? x

This paper reports on the results of the investigation of the relation between the magnetic microstructure and ferromagnetic resonance (FMR) in ferromagnetic metal-insulator composites by using granular alloys (Co₄₁Fe₃₉B₂₀) _x (SiO₂)_{1 − x} and Co _x (SiO₂)_{1 − x} as an example. A comparative analysis of the properties of FMR spectra and parameters of random magnetic anisotropy leads to correlations between these quantities. It has been found that the main mechanism that determines the FMR line width in the films under investigation is the exchange narrowing mechanism.     

Analysis of the electrical and optical properties of VBO3 single crystals and Fe1?xVxBO3 solid solutions on the basis of a many-electron model of energy band structure

A many-electron model of the energy band structure of VBO₃ and of Fe_1−x V_xBO₃ solid solutions is proposed with strong electron correlations taken into account. Experimental optical absorption spectra and data on the resistivity are discussed in the framework of the suggested model. Variation in the magnetic and electronic properties of VBO₃ and Fe_1−x V_xBO₃ under high pressure is predicted. For VBO₃, a Mott-Hubbard (insulator-metal) transition is expected in the high-pressure phase. In Fe_1−x V_xBO₃ solid solutions, a nontrivial variation in the properties is predicted, leading to the appearance of a different magnetic state. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 8, 2004, pp. 1422–1427. Original Russian Text Copyright ? 2004 by Ivanova, Kazak, Markov, Ovchinnikov, Rudenko, Abd-Elmeguid.     

Conditions favoring the polar weak ferromagnetic state in BiFeO<Subscript>3</Subscript>-type multiferroics

The crystal structure and magnetic properties of Bi_{1 − x} A _x FeO_{3 − x/2} (A = Ca, Sr, Pb, Ba), Bi_{1 − x} A _x (Fe_{1 − x} Ti _x )O₃, and Bi_{1 − x} A _x (Fe_{1 − x/2}Nb _x/2)O₃ solid solutions have been studied. It is shown that the homogeneous polar weak ferromagnetic state occurs in the vicinity of a morphotropic phase boundary in the systems where dopant ions lead to the reduction of the unit cell volume in the polar phase. In the case of A = Ca, the non-polar phase also exhibits weak ferromagnetism and the spontaneous magnetizations in the polar and nonpolar phases differ only slightly.