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1.
The ferroelectric compounds Pb2Na1−xLaxNb5−xFexO15 and Pb0.5(5−x)LaxNb5−xFexO15 (0≤x≤1) with the tungsten bronze type structure have been investigated using Raman spectroscopy. The evolution of the spectra as a function of composition at room temperature is reported. In the frequency range 200-1000 cm−1 three main A1 phonons around 240 (υ1), 630 (υ2) and 816 (υ3) cm−1 were observed. The broadening of the Raman lines for high values of x originates from a significant structural disorder. This is in good agreement with the relaxor character of these compositions. The lowest-frequency part of the spectra, below 180 cm−1, reveals a structural change in the studied solid solutions. The behaviour of the Raman shift of the υ1 mode confirms that in Pb2Na1−xLaxNb5−xFexO15, a clear anomaly occurs in the vicinity of x=0.4. 相似文献
2.
Mössbauer spectroscopy was used to probe the site-specific information of a K0.84Fe1.99Se2 superconductor. A spin excitation gap, ΔE ≈5.5 meV, is observed by analyzing the temperature dependence of the hyperfine magnetic field (HMF) at the iron site within the spin wave theory. Using the simple model suggested in the literature, the temperature dependence of the HMF is well reproduced, suggesting that, below room temperature, the alkali metal intercalated iron-selenide superconductors can be regarded as ferromagnetically coupled spin blocks that interact with each other antiferromagnetically to form the observed checkerboard-like magnetic structure. 相似文献
3.
Qingyu Xu Shengqiang ZhouZheng Wen Di WuTeng Qiu Mingxiang XuKay Potzger Heidemarie Schmidt 《Physics letters. A》2011,375(8):1209-1212
Bi(Fe1 − xMnx)O3 ceramics (x up to 0.3) were prepared by rapid sintering. Weak ferromagnetism with two magnetic anomalies at low temperatures was observed for Bi(Fe0.95Mn0.05)O3 and Bi(Fe0.9Mn0.1)O3. From temperature-dependent magnetic relaxation measurements, the anomalies at 20 K and 100 K are related to the freezing of cluster spin glass. 相似文献
4.
Magnetic properties and exchange-coupling interactions of diluted magnetic spinels A1−xA′xB2X4, where A and B are magnetic ions, namely Co1−xMgxFe2O4, were investigated using the high-temperature series expansion method (HTSE) and the distribution method of magnetic cations in the range 0≤x≤1. The magnetic phase diagram and transition temperature versus dilution x were determined using the Padé approximants method along with HTSE. The critical exponent associated with the magnetic susceptibility γ was then deduced. The obtained results are in good agreement with experimental results and critical exponent values are consistent with those suggested by the universality hypothesis. 相似文献
5.
Ali Ghasemi Andrea Paesano Jr. Carla Fabiana Cerqueira Machado 《Journal of magnetism and magnetic materials》2012
Co1−xNix/2Srx/2Fe2O4 (x=0–0.5 in steps of 0.1) ferrite nanoparticles have been synthesized at room temperature, without calcination, using a reverse micelle process. The site preference was determined by Mössbauer spectroscopy at 300 K. The hyperfine parameters were obtained, for the whole series of solid solutions. For the X≤0.20 samples, the spectra were fitted with two discrete sextets and for the X>0.20 samples, a magnetic hyperfine field distribution and a doublet were also imposed in the fit procedure. Hysteresis loops were measured using a superconducting quantum interference device magnetometer at 2 K and 300 K. The results indicate that the relative decrease in saturation magnetization of nanoparticles compared to the submicron particles could be attributed to a surface spin termination and disorder. Magnetic dynamics of the nanoparticles was studied by the measurement of ac magnetic susceptibility versus temperature at different frequencies and it is found that the results are well described by the Vogel–Fulcher model. 相似文献
6.
We report on the enhanced electromechanical, magnetic and magnetoelectric properties of Bi1−xCaxFe1−xTixO3 solid solutions. The crystal structure of the x≈0.25 compounds are close to the rhombohedral-orthorhombic phase boundary, and the solid solutions are characterized by increased electromechanical properties due to the polarization extension near the polar-nonpolar border. The homogenous weakly ferromagnetic state is established at x>0.15 doping. The chemical doping shifts the magnetic transition close to room temperature, thus enlarging the magnetic susceptibility of the compounds. The solid solutions at the morphotropic phase boundary exhibit a nearly twofold increase in piezoelectric response, whereas the magnetoelectric coupling shows five times enhancement in comparison with the parent bismuth ferrite. 相似文献
7.
Glasses in the system Ge-Se-S were prepared with different Se/S ratios in order to investigate the compositional dependence of selected physical properties. We report the results of a systematic study examining the UV-vis transmission, dc electrical conductivity and X-ray diffraction of the system Ge(SxSe1−x)2 with x=0, 0.1, 0.4 and 1.0 where replacement of S by Se was made. The changes in the optical energy gap, Eg, (from 1.95 to 2.43 eV) and band tail width, Ee, (from 103 to 243 meV) behave contrarily to the change in refractive index, n, (from 2.3 to 2) with the progressive replacement of S by Se. This behavior was discussed and interpreted with the changes in cohesive energy. The analysis of defects in the prepared films was carried out by the examination of activation energies obtained from dc electrical conductivity. The analysis of the X-ray diffraction pattern revealed a remarkable reduction in the intensity of the first and second diffraction peaks with the progressive replacement of S content, which confirms a change in the intermediate range order structure: reorganization of the structural properties. 相似文献
8.
E. Malicka T. Groń A.W. Pacyna M. Fija?kowski 《Journal of Physics and Chemistry of Solids》2011,72(8):974-979
A correlation between the second critical field Hc2 of the helix to paramagnetic transition and the magnetic specific heat C-peak was found in ZnCr2−xAlxSe4 spinel single crystals with x=0.15, 0.23. The specific heat peak is anomalously sharp for all finite magnetic fields used here and this points to a first order magneto-structural transition (from cubic to tetragonal symmetry). The C(T)-peak is increasingly suppressed as the external field increases. Approaching the Neel temperature TN, a broad ac-magnetic susceptibility peak is observed for zero dc-magnetic field. That peak does not show an energy loss and thus points towards a return to a second order type of transition. The magnetic contribution to the specific heat displays a sharp peak at TN and is maximal at the spin fluctuation temperature Tsf=34 K. Tsf is related to the maximum of the magnetic susceptibility at Tm=40 K (at 50 kOe) in the spin fluctuation region, as evidenced by the entropy exceeding 90% of the entropy calculated classically for the complete alignment of the Cr spins, (2−x)R ln(2S+1). The X-ray photoelectron spectroscopy (XPS) data indicate that Al-substitution does not affect Cr3+ 3d3 electronic configuration. 相似文献
9.
A.G. Kuchin 《Journal of magnetism and magnetic materials》2010,322(15):2215-2218
Magnetic properties of the single-crystalline Lu2Fe17−xMnx compounds, in which x=0, 0.5, and 2, with the Th2Ni17-type crystal structure are reported. The Lu2Fe17−xMnx compounds with x=0 and 0.5 are ferromagnets at low temperatures and antiferromagnets at high temperatures. The compound with x=2 is always a ferromagnet. The easy-plane magnetic anisotropy in the Lu2Fe17−xMnx ferromagnets drastically weakens with increase in Mn content up to x=2. The temperature dependence of the first magnetic anisotropy constant was obtained and compared with the single-ion model prediction. 相似文献
10.
Evgeny V. Rebrov Pengzhao Gao Tiny M.W.G.M. VerhoevenJaap C. Schouten Richard KleismitZafer Turgut Gregory Kozlowski 《Journal of magnetism and magnetic materials》2011,323(6):723-729
Nanocrystalline Co2xNi0.5−xZn0.5−xFe2O4 (x=0−0.5) thin films have been synthesized with various grain sizes by a sol-gel method on polycrystalline silicon substrates. The morphology as well as magnetic and microwave absorption properties of the films calcined at 1073 K were studied using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and vibrating sample magnetometry. All films were uniform without microcracks. The Co content in the Co-Ni-Zn films resulted in a grain size ranging from 15 to 32 nm while it ranged from 33 to 49 nm in the corresponding powders. Saturation and remnant magnetization increased with increase in grain size, while coercivity demonstrated a drop due to multidomain behavior of crystallites for a given value of x. Saturation magnetization increased and remnant magnetization had a maximum as a function of grain size independent of x. In turn, coercivity increased with x independent of grain size. Complex permittivity of the Co-Ni-Zn ferrite films was measured in the frequency range 2-15 GHz. The highest hysteretic heating rate in the temperature range 315-355 K was observed in CoFe2O4. The maximum absorption band shifted from 13 to 11 GHz as cobalt content increased from x=0.1 to 0.2. 相似文献
11.
C.S. ZhangL. Yang 《Journal of magnetism and magnetic materials》2012,324(8):1469-1472
Core-shell Co(1−x)NixFe2O4/polyaniline nanoparticles, where the core was Co(1−x)NixFe2O4 and the shell was polyaniline, were prepared by the combination of sol-gel process and in-situ polymerization methods. Nanoparticles were investigated by Fourier transform spectrometer, X-ray diffraction diffractometer, Scanning electron microscope, Differential thermal analysis and Superconductor quantum interference device. The results showed that the saturation magnetization of pure Co(1−x)NixFe2O4 nanoparticles were 57.57 emu/g, but Co(1−x)NixFe2O4/polyaniline composites were 37.36 emu/g. It was attributed to the lower content (15 wt%), smaller size and their uneven distribution of Co(1−x)NixFe2O4 nanoparticles in the final microsphere composites. Both Co(1−x)NixFe2O4 and PANI/Co(1−x)NixFe2O4 showed superparamagnetism. 相似文献
12.
Jian-Jun Li 《Solid State Communications》2004,131(8):519-522
The magnetic nanoparticles of Mn1−xCuxFe2O4 (x=0, 0.2) were prepared by using a sol-gel method. It is proved that both the MnFe2O4 and Mn0.8Cu0.2Fe2O4 nanoparticle samples have superparamagnetic feature. Although the particle sizes are the same, substitution of a small fraction Cu for Mn results in the increase of magnetocrystallite anisotropy energy, thus enhances the blocking temperature from 130 K for MnFe2O4 to 260 K for Mn0.8Cu0.2Fe2O4. Mössbauer spectroscopy confirms that the anisotropy constant K of the Mn0.8Cu0.2Fe2O4 material is distinctly higher than that of the MnFe2O4 compound. Increase of the blocking temperature suggests that the approach we employed is effective to tackle the ‘superparamagnetic limit’ problem. 相似文献
13.
G.C. DeFotis T.M. Owens W.M. May J.H. Boyle E.S. Vos Y. Matsuyama A.T. Hopkinson T.J. Wallin E.A. Welshhans 《Journal of magnetism and magnetic materials》2010,322(14):1962-1968
A new mixed magnet, Mn1−xNixCl2·H2O, is examined by dc magnetization and susceptibility measurements across the entire composition range. The pure components are quasi-one-dimensional Heisenberg antiferromagnets ordering at 2.17 K (Mn) and 5.65 K (Ni) due to weaker interchain exchange supplementing the dominant exchange along MCl2MCl2M… chemical and structural chains. High temperature magnetic susceptibilities yield Curie and Weiss constants in χM=C/(T−θ). C(x) is linear but θ(x) displays curvature, which is analyzed to show that unlike-ion exchange is ferromagnetic and similar in size to like-ion. Most notable is the absence of antiferromagnetic susceptibility maxima down to 1.6 K from x=0.10 to 0.95. For x=0.05 a susceptibility maximum appears, with Tmax almost 20% lower than in the pure Mn component but Tc reduced by 2%. The size of the susceptibility is enhanced by admixture, the effect of disrupted antiferromagnetic tendencies. Magnetization isotherms evolve with composition. Larger values of magnetization, under the same measuring conditions, occur for mixtures than for pure components, consistent with frustration, which weakens antiferromagnetic alignment tendencies. The competing ferromagnetic (Ni) and antiferromagnetic (Mn) intrachain interactions, along with disorder and low dimensional characteristics, presumably lead to the absence of magnetic order over a remarkably broad composition range. 相似文献
14.
L.V. Bau N.V. Khiem L.V. Hong P. Nordblad 《Journal of magnetism and magnetic materials》2010,322(6):753-312
Studies on La0.7Sr0.3Co1−xMnxO3 (x=0-0.5) compounds evidence that the interaction between Mn and Co ions in this system is antiferromagnetic super-exchange and not ferromagnetic (FM) double-exchange (DE). As a result, antiferromagnetism and magnetic glassiness develop steadily with increasing Mn content and the system becomes a spin glass at x∼0.1. Analyses of high-field magnetization data indicate that the system consists of two major phases: a metallic FM phase which magnetically saturates in rather low field, and an insulating non-FM phase which has a linear dependence of magnetization on magnetic field. In the low doping regime, the fraction of the non-FM component expands with temperature at the expense of the FM phase and becomes maximal at TC. Ferromagnetism reappears in highly doped (x≥0.2) compounds due to the presence of DE interaction between the Mn ions. The small volume fraction of the FM phase derived from the M(H) data in high-field region supports the coexistence of insulating and FM behaviors in the highly doped samples. 相似文献
15.
H. Yako T. Kanomata K. Endo R.Y. Umetsu A. FujitaR. Kainuma H. NishiharaK.R.A. Ziebeck 《Physica B: Condensed Matter》2012,407(3):311-315
X-ray powder diffraction and magnetization measurements have been carried out on Rh2Mn1+xSn1−x (0≤x≤0.3) alloys. The alloys, which crystallize in the L21 structure, were found to exhibit ferromagnetic behavior. The lattice constant a at room temperature decreases with increasing x, whereas the Curie temperature TC decreases linearly. At 5 K the magnetic moment per formula unit first increases with increasing x and then saturates for x≥0.2. The experimental results are discussed in terms of the influence of the Mn-Mn exchange interactions between the Mn atoms on the Sn and Mn sites. 相似文献
16.
The magnetic properties of Y2Fe17−xGax for 3≤x≤7 and Gd2Fe17−xGax for 5≤x≤7 have been investigated using 57Fe Mössbauer spectroscopy. These compounds have the rhombohedral Th2Zn17 structure. X-ray diffraction analysis of aligned powders shows that the easy direction of magnetization is parallel to the c-axis in Y2Fe10Ga7 and Gd2Fe10Ga7 and is perpendicular to the c-axis in Y2Fe14Ga3, Y2Fe12Ga5, Gd2Fe12Ga5 and Gd2Fe11Ga6. Mössbauer studies indicate that those samples are ordered ferromagnetically. The 57Fe hyperfine field decreases with increasing Ga content. This decrease results from the decreased magnetic exchange interactions resulting from Ga substitution. The average isomer shift, δ, for R2Fe17−xGax (R=Y and Gd) at room temperature is positive and the magnitude of δ increases with increasing Ga content. 相似文献
17.
M.H.R. KhanA.K.M. Akther Hossain 《Journal of magnetism and magnetic materials》2012,324(4):550-558
A series of polycrystalline ferrites having nominal chemical composition Co0.50−xMnxZn0.5Fe2O4 (0<x<0.4) have been synthesized by the solid-state reaction technique. The XRD analysis confirms single phase cubic spinel structure for all compositions. Lattice constant increases from 0.84195 to 0.84429 nm with the increasing Mn content and obeys Vegard's law. The average grain size increases by increasing both Mn content and sintering temperatures. Room temperature saturation magnetization increases for x=0.1 and decreases for increasing Mn content. The coercivity decreases with increasing Mn content due to the decrease of anisotropy constant. A reentrant spin glass behavior of these samples is observed from the zero field cooled magnetization measurements. The real part of the initial permeability increases by increasing both Mn content and sintering temperatures. This is due to the homogeneous grain growth and densification of the ferrites. The highest initial permeability 137 is observed for x=0.4 sintered at 1573 K on the other hand, the highest relative quality factor (2522) is obtained for the sample Co0.2Mn0.3Zn0.5Fe2O4 sintered at 1523 K. The Mn substituted Co0.50−xMnxZn0.5Fe2O4 ferrites showed improved magnetic properties. 相似文献
18.
We report an angle-resolved photoemission spectroscopy study of electronic structures of Eu1−xLaxFe2As2 single crystals, in which the spin density wave transition is suppressed with La doping. In the paramagnetic state, the Fermi surface maps are similar for all dopings, with chemical potential shifts corresponding to the extra electrons introduced by the La doping. In the spin density wave state, we identify electronic structure signatures that relate to the spin density wave transition. Bands around M show that the energy of the system is saved by the band shifts towards high energies, and the shifts decrease with increasing doping, in agreement with the weakened magnetic order. 相似文献
19.
P. Guzdek J. Pszczo?aJ. Chmist P. Stoch 《Journal of magnetism and magnetic materials》2011,323(5):427-431
Synthesis by arc melting, the structural and the electric properties of Y(Co1−xNix)2 alloys were studied by X-ray diffraction (XRD) and four probe dc electrical measurements. XRD analysis (300 K) shows that all samples crystallize in a cubic MgCu2-type structure. The lattice parameters linearly decrease with Ni content. Electrical resistivity for the Y(Co1−xNix)2 intermetallic series was measured in a temperature range of 15-1100 K. The parameters involved in the dependence of resistivity on temperature were determined. Residual, phonon and spin fluctuations resistivity were separated from electrical resistivity using both the Matthiesen formula and the Bloch-Gruneisen formula. The spin fluctuations resistivity of the Y(Co1−xNix)2 series are compared to the mean square amplitudes of spin fluctuations previously calculated by the Linear Muffin Tin Orbital-Tight Binding Approach method for these series in the literature. The contribution of spin fluctuations to total resistivity ρsf is proportional to T2 at low temperatures. The proportionality parameter strongly reduces across the Y(Co1−xNix)2 series. 相似文献
20.
Electrical conductivity and Seebeck coefficient for the Bi2−xYxRu2O7 pyrochlores with x=0.0,0.5,1.0,1.5,2.0 were measured in the temperature range of 473-1073 K in air. With increasing Bi content, the temperature dependence of the electrical conductivity changed from semiconducting to metallic. The signs of the Seebeck coefficient were positive in the measured temperature range for all the samples, indicating that the major carriers were holes. The temperature dependence of the Seebeck coefficient for the Y2Ru2O7 indicated the thermal activation-type behavior of the holes, while that for the Bi2−xYxRu2O7 with x=0.0-1.5 indicated the itinerant behavior of the holes. The change in the conduction behavior from semiconductor to metal with increasing Bi content is consistent with the increase in the overlap between the Ru4d t2g and O2p orbitals, but the mixing of Bi6s, 6p states at EF may not be ruled out. The thermoelectric power factors for the Bi2−xYxRu2O7 with x=1.5 and 2.0 were lower than 10−5 W m−1 K−2 and those with x=0.0,0.5,1.0 were around 1-3×10−5 W m−1 K−2. 相似文献