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1.
The SmFeTi2O7 compound has been synthesized using the solid-phase reaction method. In order to determine the magnetic state, X-ray structural, Mössbauer, calorimetric, and magnetic measurements have been performed. The state of spin glass with the freezing point T f = 7 K has been found for SmFeTi2O7.  相似文献   

2.
A Mössbauer study has been made on57Fe ions substituted into the Cu(1) site of REBa2Cu3?x Fe x O7+δ (RE=Y, Er, Dy, Gd;x=0.15, 0.30). At low temperature, the iron atoms antiferromagnetically order with a transition temperature which is dependent on the Fe concentration. The temperature dependence of the magnetic subspectra representing Fe ions with various local oxygen environments in YBa2Cu3?x Fe x O7+δ and ErBa2Cu3?x Fe x O7+δ fit a 2D-Ising model with a ratio of the anisotropic exchange between the two directions on the order of 0.5–1.0(10?3) for the Y-compounds and on the order of 1 for the Er-compounds. The magnitude of the local dopant magnetization is related to a short-range chemical order which determines the magnetic chain size and defines the correlation lengths. For the Y-compound, the order is quasi-1D with strong intrachain but very weak interchain coupling. For the Er-compounds, the magnetic coupling is Ising 2D. The strong fluctuation behavior expected in low dimensional systems above and belowT N is observed via characteristic relaxation in the Mössbauer linewidth nearT N. For both the Dy- and Gd-compounds, the magnetic order is 3D. The magnitude of the rare-earth magnetic moments appears to affect the character of the magnetic interaction in the Cu(1)-site. However, a Mössbauer effect measurement at155Gd nuclei in GdBa2Cu2.85Fe0.15O7+δ (T N(Fe)~14 K) shows paramagnetic behavior at 4.9 K.  相似文献   

3.
Results of studying the specific features of formation of the crystal structure and distribution of iron cations over the sites in the DyFeTi2O7 compound have been presented and the comparison with the GdGaTi2O7 isostructural compound has been performed. The atomic disorder in the distribution of the Fe3+ ions over structural sites in the DyFeTi2O7 compound is confirmed by the Mössbauer spectroscopy and X-ray diffractometry. The results of magnetic measurements in the low-temperature region have revealed an inflection point in the temperature dependence of the magnetic moment and its dependence on the magnetic prehistory of the sample. The obtained experimental data suggest that there is a spin glass state with freezing point T f = 6 K in the DyFeTi2O7 compound.  相似文献   

4.
The dielectric properties, X-ray emission spectra, and M?ssbauer effect in ceramics made of PbFe1/2Nb1/2O3 (PFN) compound were studied. The relaxation dynamics revealed above Curie temperature TC at a frequency of 3 × 10−2–105 Hz is described in detail. Analysis of the X-ray emission and M?ssbauer spectra showed that at room temperature (T = 300 K), the iron ions in PFN are mainly in the high-spin valence state Fe3+. The M?ssbauer spectral parameters obtained at T = (300, 353, and 393 K) indicate an octahedral environment for Fe3+ in both the ferroelectric and paraelectric phases.  相似文献   

5.
A setup for measuring cophasal and quadrature components of higher harmonics of an electromotive-force signal of the response of a high-temperature superconductor makes it possible to study nonlinear magnetic properties of superconductors in variable magnetic fields of up to 1 kOe and constant magnetic fields of up to 10 T in the temperature range of 5?C300 K. This setup was used to measure the temperature dependences of the absolute values of the real and imaginary parts of the first and third harmonics of the magnetization of textured Yba2Cu3O7 ? x polycrystalline samples in the temperature range of 77?C220 K at various values of variable and constant magnetic fields. An analysis of resulting data made it possible to reveal the presence of different dynamical modes of the magnetic flux in YBa2Cu3O7 ? x that were dominant in different temperature ranges. The nonlinearity of the magnetization of YBa2Cu3O7 ? x (the appearance of higher harmonics) was observed up to temperatures in the range of T = 103?C112 K, which were substantially higher than the temperature of the transition of this compound to a superconducting state. The observed feature in the magnetization of YBa2Cu3O7 ? x was associated with the emergence of a pseudogap state in this compound.  相似文献   

6.
237Np Mössbauer effect and magnetic susceptibility measurements of the U1?NpxO2 fluorite solid solution have been performed in the composition range 0.15 ? x ? 0.75. For x = 0.15 and 0.25, the Np ions order magnetically at a lower temperature T0 than the bulk material (TN) (T0 ~ 19 K, TN ~ 27 K for x = 0.15). For x = 0.50, T0 ~ 10 K (TN ~ 12 K from recent neutron diffraction measurements). For x = 0.75, T0TN ~ 9 K. The Np (induced) ordered moment is ~ 0.5 μB. The 237Np Mössbauer isomer shift shows that the Np ions are in a IV charge state.  相似文献   

7.
Split source57Fe Mössbauer effect spectroscopy has been performed between 4 K and 295 K on the superconducting perovskite GdBa2Cu3O7?y. No evidence is seen for magnetic splitting at low temperatures as reported in some split absorder57Fe Mössbauer experiments on this material. There is evidence for phonon mode softening, as observed for119Sn Mössbauer spectra of some other highT c superconductors.  相似文献   

8.
A new 1D coordination polymer [Fe(βAlatrz)3](ClO4)2 ? H2O (1) with a neutral bidentate ligand, βAlatrz = 4H-1,2,4-triazol-4-yl-propionate, was prepared and its magnetic behavior was investigated by temperature dependent magnetic susceptibility measurements and 57Fe M?ssbauer spectroscopy. The temperature dependence of the high-spin molar fraction derived from 57Fe M?ssbauer spectroscopy recorded on cooling below room temperature reveals a gradual single step transition with T1/2 = 173?K between high-spin and low-spin states in agreement with magnetic susceptibility measurements. 1 presents striking reversible thermochromism from white, at room temperature, to pink on quench cooling to liquid nitrogen. The phase transition is of first order as deduced from differential scanning calorimetry, with T1/2 matching the one determined by both SQUID and 57Fe M?ssbauer spectroscopy. A brief assessment has been made among closely related 1D coordination polymers to perceive the effect of ligand spacer length and anion effect on the spin crossover behavior of these new materials.  相似文献   

9.
A new type of two-dimensional antiferromagnetic structure has been investigated by magnetic susceptibility measurements, neutron diffraction and Mössbauer resonance. The magnetic cell of NaFeF4 is doubled along the a axis and the spins lie along the b axis. The κ-1 vs T curve shows a sharp minimum at about 105 K close to the three-dimensional transition temperature determined by Mössbauer spectrometry (111.5 K). A calculation of z. snfc;J/kz. snfc; has been performed using a high temperature series expansions technique (J/k = -23 K). The variation of the hyperfine field in the range 0.6 ?T/TN? 1 gave the value of the critical exponant β = 0.25.  相似文献   

10.
Mössbauer studies of ceramic samples of the antiferromagnetic perovskite PbFe2/3W1/3O3 have been carried out. It has been established that the temperature of transition to the magnetically ordered state is T N = 365 K. Iron ions in PbFe2/3W1/3O3 are found to reside in the high-spin Fe3+ state. The Fe3+ ions occupy inequivalent positions differing in the nearest cation environment, or more precisely, tungsten and iron ions are distributed in a random manner over the sites of the octahedral sublattice. The inequivalent positions arise as a result of the Fe and W ions being statistically distributed over the octahedral sublattice. For T > 0 K, magnetic fields at the nuclei and, hence, the average thermodynamic values of the magnetic moments of Fe3+ ions occupying inequivalent positions are different and, at a given temperature, are determined by the number of the nearest magnetic neighbors, with the effective magnetic fields (H eff) varying differently with temperature. As the temperature is lowered, the fields H eff level off gradually in response to the effective magnetic fields of iron ions having different numbers of exchange bonds leveling off with decreasing temperature which lowers thermal excitation.  相似文献   

11.
The Mössbauer parameters of an iron rich orthopyroxene FexMg1−xSiO3 with x = 0.87 (natural compound named XYZ) have been analyzed in detail as a function of temperature in the paramagnetic and in the magnetic region. The magnetic ordering temperature obtained by Mössbauer spectroscopy is TN = 27 ± 1 K. Above TN, a quite different behaviour of the quadrupole interactions of the Fe2+ in the M1 and M2 sites has been observed as a function of temperature. It can be explained by the different energy splittings of the orbital states of the 5T2 ground state of high spin iron (II). Below TN, using simple level scheme considerations related to the low symmetry of the Fe2+ oxygen octahedra, one can assign unambiguously the values o of the hyperfine fields to Fe2+ in M1 and M2. In this low temperature range the Mössbauer spectra can be accounted for by a distribution of hyperfine fields P(Hh.f(M1)) and P(Hh.f(M2)) related to the various Fe2+-Mg2+ nearest neighbour configurations surrounding the Fe2+ probe located on the M1 or M2 site.  相似文献   

12.
The Mössbauer spectra of YBa2(Cu1?x Fe x )3O7 at room temperature show several doublets attributed to Fe in Cu(1) sites with different oxygen configurations. Here we present a systematic study performed at 4.2 K forx=0.005, 0.01, 0.03, 0.05, 0.10, 0.15. To obtain information about the magnetic ordered state two samples, withx=0.005 andx=0.15, have been studied at 4.2 K underB ext=5 T. The Mössbauer spectra indicate that the iron moments are polarized forx=0.005, while in the ordered state (x=0.15) they have an antiferromagnetic or spin-glass-like arrangement with high anisotropy.  相似文献   

13.
The Fe‐doped system Cu0.9Ge0.9Fe0.2O3 has been investigated by means of X‐ray diffractometry, Mössbauer spectroscopy and superconducting quantum interference device. The structure of this system is orthorhombic and the lattice constants are a=4.784 Å, b=8.472 Å and c=2.904 Å, respectively. Magnetic measurements confirm that the spin‐Peierls transition appears in our sample at about 12 K, which is near to the spin‐Peierls transition temperature (T sp) 14 K of pure CuGeO3 system. The Mössbauer spectrum shows the superposition of two Zeeman sextets and a broad central line due to Fe3+ ions from room temperature to 4.2 K. The Mössbauer parameters show a discontinuity near T sp. The jump of the magnetic hyperfine field at temperatures lower than T sp means increasing of the superexchange interaction among the magnetic ions. The jump of the quadrupole splitting and the isomer shift values could be interpreted as due to decrement in symmetry of lattice sites and spontaneous thermal contraction.  相似文献   

14.
《Current Applied Physics》2015,15(3):417-422
Magnetic and Mössbauer characterization of single crystalline, sub-micron sized Bi2Fe4O9 cubes has been performed using SQUID magnetometry and transmission Mössbauer spectroscopy in the temperature range of 4.2 K ≤ T ≤ 300 K. A broad magnetic phase transition from the paramagnetic to the anti-ferromagnetic state is observed below 250 K, with the Mössbauer spectra exhibiting a superposition of magnetic, collapsed and quadrupolar spectra in the transition region of 200 K < T < 245 K. Room temperature Mössbauer spectra obtained in transmission geometry are identical to those recorded in back-scattering geometry via conversion electron Mössbauer spectroscopy, indicating the absence of strain at the surface. A small hysteresis loop is observed in SQUID measurements at 5 K, attributable to the presence of weak-ferromagnetism arising from the canting of Fe3+ ion sublattices in the antiferromagnetic matrix.  相似文献   

15.
The physical properties of DyNi2Mn doped with 57Fe have been investigated by X-ray diffraction, magnetisation (10–300?K) and 57Fe M?ssbauer spectroscopy measurements (5–300?K). DyNi2Mn(57Fe) crystallizes in the MgCu2-type cubic structure (Fd??3m space group). The ordering temperature is found to be TC?=?99(2) K, much higher than those of DyNi2 (~22?K) and DyMn2 (~35?K). Analyses of isothermal M–H curves and the related Arrott plots confirm that the magnetic phase transition at TC is second order. The magnetic entropy change around TC is 4.0?J/kg?K for a magnetic field change of 0?T to 5?T. The spectra above TC exhibit features consistent with quadrupolar effects while below TC the spectra exhibit magnetic hyperfine splitting. The Debye temperature for DyNi2Mn has been determined as θD?=?200(20) K from a fit to the variable temperature isomer shift IS(T).  相似文献   

16.
The magnetic properties of Sr7Fe10O22 have been investigated by means of magnetic susceptibility and Mössbauer absorption measurements. This compound proved to be antiferromagnetic with a Néel temperature TN = 425 K; the magnetic susceptibility is constant from the lowest measuring temperature (78 K) up to TN.The Mössbauer measurements and the analogies with “brownmillerite” type compounds indicate that iron ions occupy one octahedral and two tetrahedral different sites. An antiferromagnetic spin configuration with moments lying in the ab plane appears to be consistent with the experimental results. A small spontaneous magnetic moment was observed at room temperature with features resembling those of strontium hexaferrite; a weak ferromagnetic behavior can not however be excluded taking into account the aforementioned susceptibility behaviour.  相似文献   

17.
The results of the Mössbauer study of ferrite AgFeO2 manifesting multiferroic properties (at TT N2) have been presented. The hyperfine interaction parameters of 57Fe nuclei have been analyzed in a wide temperature range including the points of two magnetic phase transitions (T N2 ≈ 7–9 K and T N1 ≈ 15–16 K). It has been shown that the Mössbauer spectra of the 57Fe nuclei are sensitive to the variations of the character of the magnetic ordering of Fe3+ ions in the studied ferrite. The results of the model identification of a series of spectra (4.7 K ≤ TT N2) under the assumption of the cycloid magnetic structure of ferrite AgFeO2 have been presented. The analysis of the results has been performed in comparison with the literature data for other oxide multiferroics.  相似文献   

18.
The temperature dependences of the electrical resistivity ρ(T) H = const have been measured in external magnetic fields H ext (0 ≤ H ext ≤ 1420 Oe) at temperatures ranging from 70 to 273 K for samples of the granular YBa2Cu3O7 ? δ high-temperature superconductor (HTSC). Cooling of the samples to the minimum temperature T min (70 K) has been performed in external magnetic fields (FC mode) and in the absence of a magnetic field (ZFC mode). Moreover, the dependences ρ(T) H = 0 for samples cooled in the FC mode have been measured in a zero field. The curves ρ(T)H = const have been converted into isotherms of the magnetore-sistance ρ(H ext) T = const. A comparative analysis of the specific features in the behavior of the curves ρ(H) T = const for samples with different “magnetic prehistories” has made it possible to elucidate the nature and mechanisms of the influence of the particular scenario of the magnetic treatment of granular HTSCs on the behavior of their galvanomagnetic properties. The temperature dependences of the critical magnetic fields of superconducting grains (H c1g , H c2g ) and Josephson weak links (H c2J ) have been determined, and the H-T phase diagrams of granular YBa2Cu3O7 ? δ HTSCs have been recovered.  相似文献   

19.
All iron ions in the Cu1 and Cu2 local lattice sites of the YBa2(Cu0.9 57Fe0.1)3O7.01 superconductor with T c=31 K experienced magnetic ordering below T m=22 K. Therefore, at T < T m, magnetic ordering coexisted with superconductivity. According to the Mössbauer spectroscopy data, iron ions in Cu2 (Fe2) sites were in the low-spin state at T < T m(S= 3/2 or 1/2), whereas an equal number of iron ions in Cu1 (Fe1) sites were in the high-spin Fe3+ state (S=5/2). The magnetic transition near T m changed iron ion spin states-low-spin ions turned into high-spin ions, and vice versa. This preserved the spin balance between iron ions in the Cu1 and Cu2 layers. Control measurements on other samples of the YBa2(Cu1? x Fex)3O7±δ series substantiated these conclusions.  相似文献   

20.
The magnetic and electrical properties of some TTB type niobates and tantalates of EuII with general formula EuxNbO3 (0.5? x? 0.6), Eu0.5TaO3 and EuBCM5O15 (M = Ta, Nb; B = EuII, Sr, Ba; C = Na, K) have been investigated. Suceptibility measurements showed a large proportion of Eu3+ ions among the Eu2+ ions, and this was confirmed by Mössbauer spectroscopy. Mössbauer spectra also showed the absence of any magnetic ordering of the europium ions down to 4.2K, and the absence of any charge hopping phenomena up to room temperature. Conductivity and Seebeck coefficient measurements revealed typical semiconductor behaviour from 77 to 800 K. The Seebeck coefficient vs temperature curves showed a hopping conductivity regime at low temperature and an extrinsic semiconductor conductivity at high temperature. A Goodenough type of derived schematic energy level model for the tungsten bronze type structure was found to be qualitatively in agreement with the experimental results.  相似文献   

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