Mössbauer studies on Tb x Fe1−x alloy films with perpendicular magnetic anisotropy

Amorphous ferrimagnetic Tb _x Fe_1?x films with perpendicular magnetic anisotropy and Tb _x Fe_1?x /NiFe exchange-coupled structures characterized by unidirectional anisotropy are obtained. The magnetic and chemical inhomogeneity of alloys of Tb _x Fe_1?x compensation composition is established on the basis of Mössbauer studies of these systems.     

Electronic structures and local magnetic moments in ferromagnetic and antiferromagnetic FexRh1−x alloys

Ground-state magnetic properties of ordered FeRh alloys are discussed by using the realistic canonical d-band model within the Hartree-Fock and coherent potential approximations. Local magnetic moments of Fe and Rh atoms in ferromagnetic and antiferromagnetic Fe_xRh_1-x alloys are computed as a function of x, the Fe concentration. Calculated results are in good agreement with the neutron-diffraction data. The band-energy calculation indicates that in Fe-rich alloys excess Fe atoms substituted on Rh sites having larger magnetic moments than Rh atoms, play an important role in the antiferromagnetic to ferromagnetic transition observed at low temperatures.     

Hyperfine magnetic interactions in Tb(Fe1 − x Al x )2 alloys

The structural and magnetic characteristics of phase transformations in Tb(Fe_{1 ? x} Al _x )₂ alloys with concentrations x = 0?0.9 have been measured in the temperature range from 90 to 450 K. The temperature dependences of the hyperfine magnetic fields for each of local configurations of the nearest environment of iron atoms upon substitution of aluminum atoms for iron atoms have been found using Mössbauer spectroscopy.     

Structural origin of perpendicular magnetic anisotropy in Ni–W thin films

The magnetic properties and microstructure of electrodeposited Ni–W thin films (0–11.7 at% W in composition) were studied. The film structures were divided into three regions: an FCC nanocrystalline phase (0–2 at% W), a transition region from FCC nanocrystalline to amorphous phase (2–7 at% W), and an amorphous phase (>7 at% W). In the transition region, (4–5 at% W) films with perpendicular magnetic anisotropy (PMA) were found. The saturation magnetization, magnetic anisotropy field, perpendicular magnetic anisotropy and perpendicular coercivity for a typical Ni–W film (4.5 at% W) were 420 kA/m, 451 kA/m, 230 kJ/m and 113 kA/m, respectively. The microstructure of Ni–W films with PMA is composed of isolated columnar crystalline grains (27–36 nm) with the FCC phase surrounded by the Ni–W amorphous phase. The appearance of the interface between the magnetic core of Ni crystalline grains and the Ni–W non-magnetic boundary layer seems to be the driving mechanism for the appearance of PMA. The origin of PMA in Ni–W films is mainly attributed to the magnetoelastic anisotropy associated with in-plane internal stress and positive magnetostriction. The secondary source of PMA is believed to be the magnetocrystalline anisotropy of 〈1 1 1〉 columnar grains and its shape magnetic anisotropy. It is concluded that Ni–W electrodeposited films (4–5 at% W) may be applicable for perpendicular magnetic recording media.     

Crystallography,magnetic properties and magnetocaloric effect in Gd4(BixSb1−x)3 alloys

A study of magnetic and thermal properties has been carried out on the alloys from the Gd₄(Bi_xSb_1−x)₃ series with x=0, 0.25, 0.5, 0.75, and 1. All of the alloys are ferromagnetic below their respective Curie temperatures which vary from 266 K for x=0 to 332 K for x=1.0. The magnetocaloric effect calculated from the temperature and magnetic field dependencies of the magnetization and heat capacity is moderate when compared to that of other materials, which order in the same temperature range. Both the magnetic ordering and the magnetocaloric effect peak temperatures increase nearly linearly with the increasing Bi content. Experimental magnetocaloric effect data obtained from two different measurement techniques are in excellent agreement.     

Hyperfine fields and magnetic anisotropy in Fe1000−x Gd x thin films and Fe80−x GdxB20(0≤x≤24) thin films and ribbons

The Mössbauer measurements performed on Fe_100–x Gd _x thin films and on Fe_80–x Gd _x B₂₀ both as thin films and ribbons show a dependence of the spins orientation and H_hyp versus temperature, Gd content and preparation conditions. Increasing the Gd content, the initial low anisotropy disappears and H_hyp decreases. A sharp increase of the anisotopy with temperature in ribbons with low Gd concentration is evidenced.     

Structural and electronic properties of GaN x As1−x alloys

The structural and electronic properties of cubic GaN _x As_1−x with N-concentration varying between 0.0 and 1.0 with step of 0.25 were investigated using the full potential–linearized augmented plane wave (FP-LAPW) method. We have used the local density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange and correlation potential. In addition the Engel-Vosko generalized gradient approximation (EVGGA) was used for the band-structure calculations. The structural properties of the binary and ternary alloys were investigated. The electronic band structure, total and partial density of states as well as the electron charge density were determined for both the binary and their related ternary alloys. The energy gap of the alloys decreases when we move from x=0.0 to 0.25; then it increases by a factor of about 1.8 when we move from 0.25 to 0.5, 0.75 and 1.0 using EVGGA. For both LDA and GGA moving from x=0.0 to 0.25 causes the band gap to close, showing the metallic nature of the GaN_0.25As_0.75 alloy. When the composition of N moves through x=0.25, 0.5, 0.75 and 1, the band gap increases.     

Magnetic and electrical properties of Mg1−x CuxO solid solutions and magnetic shielding in Cu-Mg1−x CuxO structures

Mg_1−x Cu_xO solid solutions having an NaCl structure with 0⩽x⩽0.20 are synthesized and Cu-Mg_1−x Cu_xO structures are prepared for superconductivity studies. The magnetic susceptibility χ, electron paramagnetic resonance (EPR), and electrical conductivity of the solid solutions are studied at temperatures of 5–550 K. It is shown that χ ⁻¹(T) obeys the Curie-Weiss law with a paramagnetic Curie temperature Θ close to zero and an effective magnetic moment μ _eff=1.9 μ _B, close to the 1.73 μ _B of a Cu²⁺ ion with spin S=1/2. The width ΔH of the EPR line depends weakly on temperature and increases as x is raised. The volume narrowing of the EPR linewidth ΔH is used to estimate the exchange interaction parameter, 3×10⁻⁴ eV. The g-factor is close to 2 and is temperature independent. The electrical conductivity of Mg_1−x Cu_xO at T=300 K is ≈10⁻¹¹–10⁻¹² Ω⁻¹ cm⁻¹ for x=0 and increases to 10⁻⁵–10⁻⁶ Ω⁻¹ cm⁻¹ for x=0.15–0.20. The conductivity is p-type. Magnetic shielding is observed in Cu-Mg_1−x Cu_xO structures with x=0.15 and 0.20. The possible connection of this phenomenon with interference superconductivity in the contact layer of the structure is discussed. Fiz. Tverd. Tela (St. Petersburg) 41, 293–296 (February 1999)     

Eu valence mixture in amorphous EuxPd1−x alloys

The electronic configuration of Eu in amorphous Eu_x Pd_1−x alloys as determined by Mössbauer spectroscopy is found to change from a trivalent to a divalent state over the concentration range 0.18 ≦ x ≦ 0.35. The intermediate valence state of Eu in these alloys is characterized by a mixture of Eu occuring in two different integral valence states.     

Calculation of the temperature dependence of the thermal emf in amorphous alloys CaxAl1−x and AuxNi1−x

The temperature dependence of the thermal emf of Ca_xAl_1–x and Au_xNi_1–x for four different concentrations of the components of the alloys is calculated on the basis of the concept of dynamic concentrated excitations in amorphous metal systems. It is shown that increasing x from 0.15 to 0.50 in Au_xNi_1–x raises the thermal emf, and a further increase in the Au concentration from 0.50 to 0.80 lowers S(T). For Ca_xAl_1–x the dependence S(T) is calculated in the interval of Ca concentrations from 0.55 to 0.75. In this concentration interval the thermal emf decreases as x is increased. It is shown that for both types of alloys the S(T) curve bends abruptly at a temperature near 10T₀ (where T₀ is the concentration-dependent characteristic temperature of amorphous alloys separating the ranges of strong and weak scattering of electrons by dynamic concentration excitations). The so-called S(T) knee shifts toward lower temperatures when the thermal emf increases with increasing x and toward higher temperatures when S(T) decreases with increasing x. The results agree with experimental data.Institute of Physics of Strength and Materials Science, Siberian Branch, Russian Academy of Sciences. State University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 43–48, August, 1994.     

Magnetic and electric properties of Yb x Mn1 − x S alloys

Results from investigating the structural, magnetic, and electrical properties of Yb _x Mn_{1 ? x} S alloys (0 ≤ x ≤ 0.2) synthesized on the basis of manganese monosulfide are presented. Substituting manganese for ytterbium increases the concentration of charge carriers and lowers the activation energy. The observed anomalies in the temperature dependence of resistivity are explained by an impurity semiconductor model with donor 4f levels.     

Magnetic cluster developement in In1−x Mn x Sb semiconductor alloys

X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM) and magnetic measurements as a function of applied magnetic field and temperature for In_1?x Mn _x Sb (0.05≤x≤0.2) system are reported. Magnetic measurements performed at high and small magnetic field in ZFC and FC indicate the coexistence of ferromagnetic In_1?x Mn _x Sb solid solution and two types of magnetic cluster: ferromagnetic MnSb and ferrimagnetic Mn₂Sb. XPS valence band and Mn 2p core level spectra have confirmed the presence of MnSb and Mn₂Sb phases. TEM images show some manganese antimonide phase microinclusions with dimension between (30–40) nm.     

Magnetic anisotropy in thin films of metallic glasses Fe1−xBx alloys

Noninduced uniaxial magnetic anisotropy in Fe_1−xB_x thin films of metallic glasses was studied for 26⩽x⩽32. The samples were obtained by rf sputtering technique. Thickness and compositional dependence of uniaxial magnetic anisotropy was determined for films with thickness d⩽120 nm. The existence of the uniaxial magnetic anisotropy can be explained roughly by a directional alignment of free volume and directional order of atomic pairs in the vicinity of the free volume.     

Negatron effects in CdSe1 − x Te x and ZnS1−x Se x films

Various negatron effects in films of alloys of II–VI compounds deposited from solutions as a function of the deposition mode and heat treatment are studied. It is found that the negative photocapacitance effect, which was first discovered in ZnS_1?x Se _x films, and the slowly relaxing negative photoelectric effects, which are caused by the transition of electrons located in a nanoscale surface layer from the shallow energy levels of trapping centers to deeper levels with a lower polarizability and by the presence of nanoscale clusters in these materials, which play the role of a “reservoir” for minority charge carriers, occur according to a single mechanism. A model to explain the basic laws of negative photoconductivity in CdSe_{1 ? x} Te _x films deposited from a solution is proposed. Negative residual conductivity is explained in terms of double-barrier relief model, while negative differential photoconductivity is attributed to the presence of nanoscale electric domains.     

Ionization of an exciton moving perpendicular to a magnetic field in the GaAs/AlxGa1−x As superlattice

The magnetic field effect on the spectrum of excitons associated with various minibands in superlattices was studied by resonance Raman spectroscopy. It was found that the intensity of Raman scattering by acoustic phonons with the participation of the ground state of an exciton associated with the second miniband is sharply reduced even in weak magnetic fields if its velocity vector is orthogonal to the external magnetic field. This phenomenon was explained by the ionization of the exciton in the electric filed arising in the system of coordinate associated with the exciton moving perpendicular to the external magnetic field.     

Hyperfine fields and Fe magnetic moments in Fe−Ni invar alloys

Mössbauer spectra of Fe_1?x Ni _x withx=0.40, 0.35 and 0.32 were taken at various temperatures and fitted withB _hf distributions. TheP(B _hf) curves generally show a peak and a low-field tail. The peakB ^* and the average \(\bar B\) were obtained in theT→0 limit. Fe moments were deduced from these data with help of a semiempirical equation. While the average \(\bar \mu _{Fe} \) decreases withx (invar anomaly), a large fraction of Fe atoms retain the strong moment (≈ 2.7 μ_B) typical of Ni-rich alloys. This result is consistent with a two-states model for invar.     

NixPt1−x/Rh(111): A stable surface alloy with enhanced magnetic moments

We have performed ab initio density functional theory calculations to investigate the miscibility and magnetic properties of pseudomorphically grown monolayers of Ni_xPt_1?x surface alloys on a Rh(111) substrate. We find that the formation of this alloy is energetically favored over phase-segregated forms, and its magnetic moment is also enhanced. A significant contribution to this enhanced magnetic moment is found to come from the induced moments on the otherwise non-magnetic elements Pt and Rh. A low concentration of Ni gives rise to a high magnetic moment per Ni atom. We find that a low effective coordination and a high non-spin-polarized density of states at the Fermi level are responsible for these enhanced moments.     

The behavior of Shubinikov-de Haas oscillations in Hg1−x−yCdxMnyTe alloys

The transverse and longitudinal magnetoresistance are measured on a quaternary semimagnetic semiconductor, n-type Hg_1−x−yCd_xMn_yTe with 0.01 < x < 0.23 and y ≈ 0.14, at different temperatures. The peaks of the Landau-spin states are assigned using the selection rules already developed for HgCdTe. The Landau-spin states are modified by an exchange interaction between the Mn²⁺ ions localized spin and the band electrons, thus it becomes possible to compare directly the extent of the spin modification between the negative gap side and the open gap side of the new alloys.