Cluster glass-like behavior of the diluted antiferromagnet Fe x Mg1−x TiO3 (x=0.2,x=0.3)

A diluted antiferromagnet Fe _x Mg_1–x TiO₃ has been shown to behave as a spin glass (x=0.2) and a reentrant spin glass (x=0.3) near the Fe percolation concentrationx 0.25. In order to obtain microscopic information on these samples, we performed Mössbauer measurements. At considerably higher temperatures than the transition temperatures, magnetically broadened spectra appear superimposed upon the paramagnetic doublets. A remarkable feature is that the intensity of the magnetic spectra increases accompanying the decrease of their linewidth. This behavior can be ascribed to the gradual slow-down of fluctuations of the antiferromagnetic clusters formed at high temperatures. To investigate the temperature variations of the relaxation time of the clusters, we analyzed the Mössbauer spectra using the method formulated by Blume. It has been shown that becomes long with decreasing temperature and the rate of the slow-down of is hastened aroundT _SG andT _N.     

Thermal destruction of antiferromagnetic Fe-Fe exchange bonds and mechanism of the transition to the spin-glass state in (Fe0.65Ni0.35)1−x Mnx systems with antiferromagnetic competing exchange interactions

The thermal evolution of the competition between the ferro-and antiferromagnetic exchange interactions in (Fe_0.65Ni_0.35)_1?x Mn_x alloys, which display different magnetic properties, depending on composition and temperature, is investigated. The distribution functions of the magnetic hyperfine fields P(B _hf) for ⁵⁷Fe are determined by Mössbauer spectroscopy in the temperature range 5–300 K for the alloys with x=0, 0.024, 0.082, 0.136, 0.195, and 0.252. The temperature dependence of the integrated intensity I _s (T) is analyzed for the low-and high-field portions of P(B _hf). The features found in the behavior of I _s (T) are interpreted as results of variation of the ratio between the competing exchange interactions of different signs as a result of the thermal destruction of antiferromagnetic Fe-Fe exchange bonds. It is shown that the changes in the spin structure in the low-temperature range are due to the thermal destruction of Fe-Fe exchange bonds. One of the consequences of this destruction is “reentrance” (an increase in the hyperfine field with increasing temperature for some of the Fe atoms). The relationship between the thermal destruction of Fe-Fe exchange bonds and the magnetic transitions of the Fe-Ni-Mn system to the spin-glass state is considered.     

Local configurations and atomic intermixing in as-quenched and annealed Fe1−xCrx and Fe1−xMox ribbons

Local atomic configuration, phase composition and atomic intermixing in Fe-rich Fe_1?xCr_x and Fe_1?xMo_x ribbons (x = 0.05, 0.10, 0.15), of potential interest for high-temperature applications and nuclear devices, are investigated in this study in relation to specific processing and annealing routes. The Fe-based thin ribbons have been prepared by induction melting, followed by melt spinning and further annealed in He at temperatures up to 1250 °C. The complex structural, compositional and atomic configuration characterisation has been performed by means of X-ray diffraction (XRD), transmission Mössbauer spectroscopy and differential scanning calorimetry (TG-DSC). The XRD analysis indicates the formation of the desired solid solutions with body-centred cubic (bcc) structure in the as-quenched state. The Mössbauer spectroscopy results have been analysed in terms of the two-shell model. The distribution of Cr/Mo atoms in the first two coordination spheres is not homogeneous, especially after annealing, as supported by the short-range order parameters. In addition, high-temperature annealing treatments give rise to oxidation of Fe (to haematite, maghemite and magnetite) at the surface of the ribbons. Fe_1?xCr_x alloys are structurally more stable than the Mo counterpart under annealing at 700 °C. Annealing at 1250 °C in He enhances drastically the Cr clustering around Fe nuclei.     

Ionic and electronic conductivity in CaTi1−xFexO3−δ (x=0.1–0.3)

Electrical conductivity measurements on CaTi_1?xFe_xO_3?δ (x=0.1, 0.2, 0.3) were performed on polycrystalline pressed and sintered tablets using the van der Pauw four point method in controlled atmospheres. The results were interpreted to reflect n-type, ionic and p-type conductivity at different oxygen partial pressures. An increasing iron content increases the number of oxygen vacancies and increases the ionic conductivity at high temperatures, but also increases the tendency of ordering, which suppresses the ionic conductivity at more moderate temperatures. These findings are in accordance with the phase diagram of the system CaTiO₃-CaFeO_2.5 based on X-ray and Mössbauer studies.     

Shubnikov-de Haas effect in tricrystals of the system of alloys Bi1−x Sbx (x=0.1; 0.13) with n-type conductivity

The Shubnikov-de Haas effect has been investigated in tricrystals of the alloy system Bi_1−x Sb_x (x=0.1; 0.13) with n-type conductivity in stationary (up to 14 T) and pulsed (up to 40 T) magnetic fields. Reconstruction of the internal boundary of the tricrystals was observed, along with a number of new component oscillations of ρ(B) indicating a rotation of the constant-energy surfaces of the L electrons on the intercrystallite boundary at an angle of ∼74° in the binary-trigonal plane. Fiz. Tverd. Tela (St. Petersburg) 41, 991–993 (June 1999)     

Hyperfine interactions in R x Gd1− x Fe3 intermetallics R = Tb,Y

The structural and magnetic properties of rare earth iron intermetallic compounds Tb _x Gd_1?x Fe₃ and Y _x Gd_1?x Fe₃ (x = 0. 0, 0. 1, 0. 2, 0. 4, 0. 5, 0. 6, 0. 8, 1. 0) was studied by X-ray diffraction, the ⁵⁷Fe Mössbauer effect and SQUID measurements. All investigated compounds crystallize in the rhombohedral PuNi3-type of crystal structure. The investigation of magnetic properties of R _x Gd_1?x Fe₃ proved their ferrimagnetic behavior. The Curie temperature of the investigated compounds decreases with the increase of R concentration from 721K (GdFe₃) to 655K (TbFe₃) and 533K (YFe₃). The saturation magnetic moment MS in the R _x Gd _1?x Fe₃ system increase with x parameter. The Mössbauer spectra are analyzed using four sextets, corresponding to three crystallographically (b, c, h) and four magnetically (b, c, h₁, h₂) inequivalent sites for iron. The mean hyperfine magnetic field increases with increase of the Gd concentration     

Structural features of the system of cubic crystals Zn0.999Fe0.001S1 ? x Se x (x = 0, 0.2)

The structural state of cubic single crystals Zn_0.999Fe_0.001S_{1 ? x} Se _x (x = 0, 0.2) obtained by the chemical transport method has been investigated using thermal neutron diffraction for the first time. It has been found that the diffraction patterns of these crystals contain the previously unknown effects of diffuse scattering caused by local statistic atomic displacements in the metastable fcc lattice.     

Electronic structure of Rh, Pt, In, and Sn in the mixed-valence systems Eu(Rh1−x Ptx)2 and U(In1−x Snx)3

The electronic structure of Rh, Pt, In, and Sn in the mixed-valence systems Eu(Rh_1−x Pt_x)₂ and U(In_1−x Sn_x)₃ has been studied by the x-ray K line-shift method. It has been found that the occupation of the Rh 4d-shell in Eu(Rh_1−x Pt_x)₂ is higher than that in the metal, and that it grows with decreasing Eu valence (i.e., with increasing 4f-shell occupation). The electronic structure of Pt, In, and Sn in Eu(Rh_1−x Pt_x)₂ and U(In_1−x Sn_x)₃ does not depend on the Eu and U valence and is practically the same as in the metals. These features in the electronic structure of Rh, Pt, In, and Sn in Eu(Rh_1−x Pt_x)₂ and U(In_1−x Sn_x)₃ suggest that the electron released in the f ⁿ → f ⁿ −1+e transitions, rather than transferring to the common conduction band, remains localized at the Eu and U atoms. Fiz. Tverd. Tela (St. Petersburg) 41, 1529–1531 (September 1999)     

Phase stratification in the Nd1 − x BaxCoO3 − δ (0.3 ≤ x ≤ 0.54) system

Slowly cooled Nd_{1 ? x} Ba_xCoO_{3 ? δ} samples were two-phase in the concentration interval 0.3 ≤ x ≤ 0.46. One of the phases had O-orthorhombic lattice distortions (Pbnm) characteristic of ferromagnetic samples with x ≤ 0.3, and the other phase had tetragonal distortions (P4/mmm) characteristic of samples with x ≥ 0.46. Tetragonal distortions were caused by ordering of Nd³⁺ and Ba²⁺ ions. Samples with ordered neodymium and barium ions (Nd_{1 ? y} Ba_{1 + y} Co₂O_{6 ? γ} at ?0.08 ≤ y ≤ 0.08) experienced metal-dielectric and orientation magnetic phase transitions.     

Cation Radii and Oxygen Deficiency Effects on the Structural,Magnetic, and Electrical Properties in La 1− x Sr x MnO 3−δ □ δ Manganites ( x = 0.2-0.5 and δ = 0.1)

The series of non-stochiometric strontium substituted lanthanium manganites La 1 m x Sr x MnO 3 m i i ( i = 0.1, x = 0.2-0.5) has been studied and show the effect of oxygen deficiency on the structural transition, magnetic and electrical properties of these compounds. Polycrystalline samples La 1 m x Sr x MnO 3 m i i were synthesised by a new method at atmospheric pressure. In this series of manganites, the Mn 4+ content is systematically decreased due to increase in the non-stoichiometry. X-ray diffraction analysis shows a phase transition from orthorhombic to rhombohedral systems for 0.2 h x h 0.5. The material is ferromagnetic for 0.3 h x h 0.5 and antiferromagnetic for x = 0.2. The Curie temperature T C increases with increasing x . The resistivity as a function of temperature shows that samples with x = 0.3 and ferromagnetic metal between T CF and T P becomes ferromagnetic insulators below T CF where charge-ordering seems to appear.     

Ordering of atoms in 3d sublattice of the intermetallic quasibinary system Dy(Fe1−xMnx)2

Methods of x-ray analysis and nuclear -resonance (Mössbauer effect) have been used to study the distribution of iron and manganese atoms in the intermetallic quasibinary system Dy(Fe_1–xMn_x)₂, which is isostructural to the Laves phase C15. Ordering of atoms of transition metals has been found in 3d sublattice of intermetallic compounds Dy(Fe_1–xMn_x)₂ with the formation of a triple superstructure having the stoichiometric composition Dy(Fe_0·.25Mn_0·.75)₂.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 55–60, June, 1986.     

Magnetic properties and Eu hyperfine interactions in EuSr2Ru1−xO6 (x=0 and 0.2)

Magnetization studies show that nonsuperconducting RSr₂Ru_1−xCu_xO₆ (R=Eu and Gd) compounds are magnetically ordered below T_N=31 K regardless of R and Cu concentration. The magnetic ordering is due to the Ru sublattice. Mössbauer effect studies reveal that the Ru magnetism induces a magnetic moment (0.35 μ_B) and a magnetic hyperfine field (270 kOe) in the otherwise nonmagnetic Eu³⁺ ions, and that the Ru magnetization lies in the basal plane.     

Anomalous spin relaxation and quantum criticality in Mn1 − x Fe x Si solid solutions

We report results of the high frequency (60 GHz) electron spin resonance (ESR) study of the quantum critical metallic system Mn_{1 ? x} Fe _x Si. The ESR is observed for the first time in the concentration range 0 < x < 0.24 at temperatures up to 50 K. The application of the original experimental technique allowed carrying out line shape analysis and finding full set of spectroscopic parameters, including oscillating magnetization, line width and g factor. The strongest effect of iron doping consists in influence on the ESR line width and spin relaxation is marked by both violation of the classical Korringa-type relaxation and scaling behavior. Additionally, the non-Fermi-liquid effects in the temperature dependence of the ESR line width, which may be quantitatively described in the theory of Wölfle and Abrahams, are observed at quantum critical points x* ～ 0.11 and x _c ～ 0.24.     

Investigation of the character of the exchange interaction in the system Hg1−xMnxSe

A new method is proposed for determining the magnetic characteristics (magnitude and sign of the exchange interaction energy and the average size of clusters of magnetic ions) of dilute solid solutions of semimagnetic semiconductors at low temperatures based on oscillation measurements. The method makes it possible to find the magnetic characteristics of the indicated systems at temperatures between the point of the transition into the spin glass state and the temperature corresponding to the characteristic binding energy of magnetic atoms in clusters, for which standard methods based on the measurement of the magnetic susceptibility are not effective. The method is used to study the character of the exchange interaction in the system of solid solutions Hg_1–xMn_xSe as a function of their composition as well as under conditions of hydrostatic compression. To this end the oscillations of the magnetoresistance (Shubnikov-de Haas (SH) effect) in single-crystalline samples of Hg_1–xMn_xSe in the region of compositions 0.001 x 0.23 in magnetic fields H up to 65 kOe at temperatures T = (0.4–20) K and pressures up to 16 kbar were studied.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 29–39, November, 1989.     

The influence of the local surrounding on the hyperfine interactions in Zr(Fe1−x Ni x )2 compounds

Mössbauer spectroscopy and the TDPAC method have been used to study Zr(Fe_1–x Ni _x )₂ compounds forx0.30. The hyperfine magnetic field at the Fe sites and the quadrupole splitting as functions of nickel concentration were analysed by use of⁵⁷Fe Mössbauer spectroscopy. Values of the internal magnetic field on¹⁸¹Ta nuclei have been found by means of the TDPAC method.     

Interplay of the doped Ge atoms and the N vacancies with the negative thermal expansion of M3(Cu1−x Ge x )N1−y

The giant negative thermal expansion (NTE) found in the anti-perovskite manganese nitride could be controlled by the content of the doped Ge and the vacancies of N. In this paper, the origin of such a tunable thermal expansion behavior is systematically studied. Our calculations indicate that the doped Ge atoms enhance the NTE property of the compound, and the existing N vacancies have a weak influence on the NTE property. Furthermore, the change of the exchange parameters between Mn ions with the content of the doped Ge as well as with the N vacancies in the compound is revealed, from which the relative stabilities of different magnetic phases in the concerned compounds can be explained.     

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.     

Effect of sintering temperature on the chemical state of ions in the Ba1 − x Sr x TiO3 (x = 0.2) system,according to X-ray photoelectron spectroscopy data

The chemical state of ions in different samples of ceramics of the Ba_{1 ? x} Sr _x TiO₃ (x = 0.2) system produced by varying only a single technological parameter (sintering temperature T _S) is studied by means of X-ray photoelectron spectroscopy. The X-ray electron spectra of the Ba4d, Sr3d, O1s, and Ti2p levels reveal well-marked fine structures. As expected, the energy position and intensity of the features of this fine structure vary with T _S.     

Thermoelectric properties of magnetic configurations of graphene-like nanoribbons in the presence of Rashba and spin–orbit interactions

In this paper we investigate the influence of spin–orbit interaction and two types of Rashba interaction (intrinsic and extrinsic) on magnetic and thermoelectric properties of graphene-like zigzag nanoribbons based on the honeycomb lattice. We utilize the Kane-Mele model with additional Rashba interaction terms. Magnetic structure is described by the electron-electron Coulomb repulsion reduced to the on-site interaction (Hubbard term) in the mean field approximation. We consider four types of magnetic configurations: ferromagnetic and antiferromagnetic with in-plane and out-of plane direction of magnetization. Firstly, we analyze the influence of extrinsic Rashba coupling on systems with negligible spin–orbit interaction, e.g. graphene of an appropriate substrate. Secondly, we discuss the interplay between spin–orbit and intrinsic Rashba interactions. This part is relevant to materials with significant spin–orbit coupling such as silicene and stanene.     

X-ray photoelectron and mössbauer spectroscopy studies of the valence state of transition metal ions in Co1–x Fe x Cr2O4 (x = 0.1, 0.2, 0.5) ceramics

The valence state of transition metal ions in the Co_1–x Fe _x Cr₂O₄ (x = 0.1, 0.2, 0.5) system has been investigated using X-ray photoelectron and Mössbauer spectroscopy. It has been shown that, in this system, there are Fe²⁺ and Fe³⁺ ions. The relative Fe³⁺/Fe²⁺ contents have been determined by fitting the experimental Fe 2p photoelectron spectra by a superposition of theoretical spectra of the Fe²⁺ and Fe³⁺ ions, as well as using Mössbauer spectroscopy.