共查询到20条相似文献,搜索用时 15 毫秒
1.
Pedro A. Montano Yinwan Li J.F. Mitchell P.E. Mijnarends S. Kaprzyk A. Bansil 《Journal of Physics and Chemistry of Solids》2004,65(12):1999-2004
Magnetic Compton profiles have been measured for the colossal magnetoresistance manganites La1.2Sr1.8Mn2O7 and La0.7Sr0.3MnO3, and for magnetite Fe3O4, along various crystallographic directions, over a wide range of temperatures and magnetic fields. The experimental results are interpreted via first-principles computations for the double layer manganite, La1.2Sr1.8Mn2O7, and by using a simple model involving atomic d-orbitals and free electrons for the other two compounds. For all three materials a preference for the occupation of eg orbitals is found, particularly, for orbitals of dx2−y2 symmetry. An itinerant electron contribution is adduced at all temperatures in magnetite; such a contribution also appears in La1.2Sr1.8Mn2O7, but it is present only at low temperatures in La0.7Sr0.3MnO3. 相似文献
2.
Y. Tazuke 《Physics letters. A》1979,69(5):341-343
The electrical resistivity and magnetization of VxCr3?xS4 (x = 0.0 - 1.0) have been measured. Weak ferromagnetic moments are observed at low temperatures for x ≠ 0.0. Curie temperatures are determined from magnetization curves and resistivity anomalies. 相似文献
3.
The magnetic and magnetoresistive properties of spinel-type Zn1−xCoxFe2O4 (x=0, 0.2 and 0.4) ferrites are extensively investigated in this study. A large negative magnetoresistance (MR) effect is observed in Zn1−xCoxFe2O4 ferrites of spinel structure. These materials are either ferrimagnetic or paramagnetic at room temperature, and show a spin-(cluster) glass transition at low temperatures, depending on the chemical compositions. The MR curves as a function of magnetic fields, MR(H), are parabolic at all temperatures for paramagnetic polycrystalline ZnFe2O4. The MR for ZnFe2O4 at 110 K in the presence of 9 T applied magnetic field is 30%. On the other hand, MR(H) are linear for x=0.2 and 0.4 ferrimagnetic Zn1−xCoxFe2O4 samples up to 9 T. The MR effect is independent of the sintering temperatures, and can be explained with the help of the spin-dependent scattering and the Yafet–Kittel angle of Zn1−xCoxFe2O4 mixed ferrites. 相似文献
4.
Systematic studies of X-ray, magnetic, electronic transport, and elastic properties have been performed on polycrystalline Bi0.5Ca0.4Sr0.1MnO3 sample. The sample exhibits charge ordering (CO) state below TCO (=304 K), accompanied by a distinct maximum in magnetization. The softening of Young's modulus in the vicinity of TCO indicates that there is a strong coupling of electron-phonon due to Jahn-Teller (JT) effect. The dynamic ferromagnetic spin correlations are observed at high temperatures above TCO, which are replaced by antiferromagnetic (AFM) spin fluctuations at a concomitant CO transition. Below 32 K, a spin-glass (SG) state dominates at low temperatures. The voltage-current (V-I) characteristics measurement results indicate that the non-linear conduction starts above a threshold current, giving rise to a region of negative differential resistance (NDR). The origin of the non-linear conduction is discussed in view of current induced collapse of CO state associated with phase-separation mechanism. 相似文献
5.
Xian-Sheng Cao 《Physics letters. A》2008,372(32):5356-5360
In this Letter the microscopic theory of the relative change in velocity of sound with temperature of La0.5Ca0.5MnO3 is reported. The phonon Green function is calculated using the Green function technique of Zubarev in the limit of zero wave vector and low temperature. The lattice model electronic Hamiltonian in the presence of the phonon interaction with hybridization between the conduction electrons and the l-electrons is used. The relative change in velocity of sound at various temperatures is studied for different model parameters namely the position of the l-level, the effective phonon coupling strength and hybridization strength. The phonon anomalies observed experimentally at different temperatures are explained theoretically. An abrupt change in velocity at Neel temperature (TN) is observed clearly. It is observed that different parameters influence the velocity of sound. 相似文献
6.
A.A Abu-SehlyM.I Abd-Elrahman 《Journal of Physics and Chemistry of Solids》2002,63(1):163-170
The optical absorption of the As-prepared and annealed As45.2Te46.6In8.2 thin films are studied. Films annealed at temperatures higher than 453 K show a decrease in the optical energy gap (Eo). The value of Eo increases from 1.9 to 2.43 eV with increasing thickness of the As-prepared films from 60 to 140 nm. The effect of thickness on high frequency dielectric constant (?∞) and carrier concentration (N) is also studied. The crystalline structures of the As45.2Te46.6In8.2 thin films resulting from heat treatment of the As-prepared film at different elevated temperatures is studied by X-ray diffraction. An amorphous-crystalline transformation is observed after annealing at temperatures higher than 453 K. The electrical conductivity at low temperatures is found due to the electrons transport by hopping among the localized states near the Fermi level. With annealing the films at temperatures higher than 473 K (the crystallization onset temperature) for 1 h, the electrical conductivity increases and the activation energy decreases, which can be attributed to the amorphous-crystalline transformations. 相似文献
7.
S. Mizusaki N. Kawamura Y. Nagata A. Sato H. Samata 《Journal of magnetism and magnetic materials》2010,322(13):L19
The single crystal of the new ternary compound Sm12Fe14Al5 was grown and its crystallographic and magnetic properties were investigated. Sm12Fe14Al5 has a hexagonal structure of the space group p-3m1 and shows ferromagnetism with a Curie temperature of 245 K. The easy direction of magnetization is parallel to the c-axis at temperatures between 245 and 85 K; however, it changes to the c-plane below 85 K through a first-order-like phase transition. No saturation is observed in the magnetization curve even under the applied field of 55 kOe at 5 K. Sm12Fe14Al5 seems to have a large coercive field at very low temperatures. The anisotropy field was estimated at 5 and 120 K and the saturation magnetization of low temperature phase is explained assuming a ferromagnetic coupling between Fe and Sm sublattices. 相似文献
8.
Sohei Okazaki Noriaki Okazaki Hidetaka Sugaya Ryota Takahashi Yuji Matsumoto Hideomi Koinuma Tetsuya Hasegawa 《Applied Surface Science》2006,252(7):2615-2621
We developed a scanning microwave microscope (SμM) designed for high-throughput electric-property screening as well as for rapid construction of electronic phase diagrams at low temperatures. As a sensor probe, we used a high-Qλ/4 coaxial cavity resonator to which a thin needle with ball-tip end was attached. The sensor module was mounted on the low-temperature XYZ stage, which allowed us to map out the change of resonance frequency and quality factor due to the local tip-sample interaction at low temperatures. From the measurements of combinatorial thin films, such as Ti1−xCoxO2−δ and Nd0.9Ca0.1Ba2Cu3O7−δ (NCBCO), it was demonstrated that this SμM system has enough performance for the high-throughput characterization of sample conductance under variable temperature conditions. 相似文献
9.
Christophe Lerot Jean-Pierre Bouanich Muriel Lepère 《Journal of Molecular Spectroscopy》2006,235(2):196-205
The N2- and O2-broadening coefficients of 33 rovibrational lines in the ν2 and ν5 bands of 12CH3F were measured at 183 K using a diode-laser spectrometer. The measurement of these coefficients was also realized at room temperature for 10 of these lines to determine their temperature dependence. The line parameters were obtained by fitting to the experimental profile the Voigt lineshape, and the Rautian and Galatry models taking into account the collisional narrowing. Calculations of the pressure-broadening coefficients were also performed for the same temperatures from a semiclassical model involving electrostatic, induction and dispersion interactions in the intermolecular potential. The calculated values reproduce well the experimental data for both temperatures and both perturbers and the theoretical temperature dependence of the broadening coefficients is in satisfactory agreement with that derived from the measurements. 相似文献
10.
P. NishaS. Savitha Pillai K.G. SureshManoj Raama Varma 《Journal of magnetism and magnetic materials》2012,324(1):37-43
The influence of partial substitution of La by Dy on the magnetocaloric response of (La1−xDyx)0.67Ca0.33Mn0.9V0.1O3, where x=0.03, 0.15 and 0.25 is studied. Rietveld refinement of X-ray diffraction pattern using GSAS method shows that the compounds adopt the orthorhombic structure with Pnma space group. The systematic change in lattice parameters and magnetic phase transition indicates the substitution effect of Dy. From the magnetization isotherms at different temperatures, magnetic entropy change close to their respective transition temperatures (TC) has been evaluated. The maximum value of entropy change near TC is found to be about 4.8 J/kg K at 187.5 K for LCMVDy0.03, 2.45 J/kg K at 107.5 K for LCMVDy0.15 and 2.15 J/kg K at 92.5 K for LCMVDy0.25 at 4 T. Dy addition produces a reduction in TC and in magnitude of the magnetic entropy change. Even though the entropy change decreases with increasing Dy substitution the refrigerant temperature range, ΔT, is found to be 10 K for LCMVDy0.03, 31 K for LCMVDy0.15 and 35 K for LCMVDy0.25 compounds [90%] at 4 T. The field dependence of the magnetic entropy change is also analyzed showing the power law dependence, ΔSM∞Hn where n=0.75(2) for LCMVDy0.03, n=0.80(4) for LCMVDy0.15 and n=0.92(8) for LCMVDy0.25 compounds at their respective transition temperatures. The relative cooling power and its field dependance are also analyzed. 相似文献
11.
The influence of dc current on the resistivity ρ and the Young's modulus E of La0.5Ca0.5MnO3 compound has been investigated by means of an in situ measuring method. At low temperatures, both the resistivity ρ and the relative modulus ΔE increase with the current. A relaxation behavior of ρ to the higher resistive state is observed at a fixed temperature and a constant current. After storing the sample for a few days, ρ decreases with the current, accompanying a slight drop of ΔE at low temperatures. Current-induced effects on ρ and ΔE are interpreted according to the current-induced interwinning of Mn3+O6 octahedral distortion modes between Q2- and Q3-types, which is suggested to contribute to the variation of the resistivity. 相似文献
12.
El?bieta Jartych Mariusz Mazurek Dionizy Czekaj 《Journal of magnetism and magnetic materials》2010,322(1):51-55
X-ray diffraction and Mössbauer spectroscopy were applied as complementary methods to investigate the structure and hyperfine interactions in the series of Bim+1Ti3Fem−3O3m+3 Aurivillius compounds with m=4, 6, 7 and 8. Samples were synthesized by the solid-state sintering method at various temperatures. As X-ray diffraction analysis proved, the compounds formed single phases at temperature above 993 K. Mössbauer studies have confirmed diffraction measurements. Compounds synthesized at 993 K contained residual hematite, however these sintered at elevated temperatures were single-phased materials. Room-temperature Mössbauer spectra of Bim+1Ti3Fem−3O3m+3 compounds revealed their paramagnetic properties, what is consistent with the literature data concerning the Néel temperature of these ceramics (TN is smaller than room temperature). Detailed analysis of MS spectra allowed to state that iron ions may occupy both tetrahedral and octahedral sites in the crystallographic lattice of Aurivillius compounds. 相似文献
13.
The resistivity of RECu2Si2 compounds contains a term which is due to a mixture of spin and aspherical Coulomb scattering. The disorder resistivities and the ordering temperatures scale well with each other but deviate strongly from the de Gennes factor. The deviations scale with an anomaly of the c/a ratio which develops at low temperatures for the RE ions with L ≠ 0. 相似文献
14.
The linear and nonlinear low field AC susceptibilities of Zn0.75Co0.25Fe0.5Cr1.5O4 show peaks due to non-critical contributions, which mask the peak due to spin glass ordering. They extend into the region of temperatures in which Mössbauer spectra do not show any magnetic component. When a DC field of 200 Oe suppresses the non-critical contributions, peak due to spin glass ordering is clearly visible. The spin glass ordering is thus shown to be a thermodynamic transition. The critical exponent is found to fall within the range found using other spin glasses. Mössbauer spectra in zero fields provide TSG, which agrees with the peak temperature of AC susceptibilities in the absence of non-critical contributions. 〈SZ〉 determined using Mössbauer spectra does not show any anomaly. In the presence of a field of 5 T, the spectra show SG ordering at 4.2 K, which converts into ferrimagnetic ordering at higher temperatures. 相似文献
15.
Annealing temperature dependence of the stress-induced magnetic anisotropy in Co73Mo2Si15B10 (λs < 0) and (Co0.89Fe0.11) 72Mo3Si15B10 (λ > 0) metallic glass ribbons has been studied experimentally. The room temperature values of the induced anisotropy constants K depend strongly on the annealing conditions, and reveal a change of sign at annealing temperatures well below Tcryst. It is concluded that transient creep and steady-state creep at the elevated temperature give rise to compressive and tensile stresses, respectively, in the expression for the magnetoelastic coupling energy at room temperature. 相似文献
16.
C. Karthik 《Journal of Physics and Chemistry of Solids》2006,67(12):2437-2441
The complex dielectric and AC conductivity response of BaBi2Nb2O9 relaxor ferroelectric ceramics were studied as a function of frequency (100 Hz-10 MHz) at various temperatures. The observed dielectric behavior was characterized by two types of relaxation processes which were described by the ‘universal relaxation law’. The frequency dependence of conductivity which showed a classical relaxor behavior followed the Jonscher's universal law σ(ω)=σ0+Aωn. The exponent n exhibited a minimum in the vicinity of temperatures of dielectric anomaly while the pre-factor A showed a maximum. The temperature dependence of n followed the Vogel-Fulcher relation with activation energy of about 0.14 eV. 相似文献
17.
The complex ac dynamic magnetic susceptibility was used to study the influence of temperature on critical fields in polycrystalline ZnCr2Se4 spinel. An antiferromagnetic order with a Néel temperature TN=20.7 K and a strong ferromagnetic exchange evidenced by a positive Curie-Weiss temperature θCW=55.1 K were established. An increasing static magnetic field shifts TN to lower temperatures while a susceptibility peak at Tm in the paramagnetic region—to higher temperatures. The non-zero and negative values both of the second and third harmonics of susceptibility suggest only a parallel spin coupling in ferromagnetic clusters in the range between the Néel and Curie-Weiss temperatures. Below TN the magnetic field dependence of susceptibility, χac(H), shows two peaks at critical fields Hc1 and Hc2. The values of Hc1 decrease slightly with temperature while the values of Hc2 drop rapidly with temperature. The strong changes of Hc2 temperature induced are mainly responsible for a spin frustration of the re-entrant type in the spinel under study. 相似文献
18.
In this paper, the microscopic theory of the relative change in velocity of sound with temperature of La0.5Ca0.5MnO3 is reported. The phonon Green function is calculated using the Green function technique of Zubarev in the limit of zero wave vector and low temperature. The lattice model electronic Hamiltonian in the presence of the phonon interaction with hybridization between the conduction electrons and the l-electrons is used. The relative change in velocity of sound at various temperatures is studied for different model parameters, namely the position of the l-level, the effective phonon coupling strength and hybridization strength. The phonon anomalies observed experimentally at different temperatures are explained theoretically. An abrupt change in velocity at Neel temperature (TN) is observed clearly. It is observed that different parameters influence the velocity of sound. 相似文献
19.
The diffusion of 55Fe has been measured parallel to the c axis of Fe2O3 single crystals at temperatures in the range 708–1303°C and at an oxygen activity of unity. The tracer penetration profiles were determined using sectioning techniques. For temperatures above 900°C the tracer diffusion coefficient is given byD1(Fe) = 1.6 × 109 exp[?6.0 (eV)/kT] cm2 s?1 and below 900°C by 2.8 × 10?9 exp[?1.8 (eV)kT]. The high-temperature behaviour is probably characteristic of pure Fe2O3, whereas diffusion at lower temperatures may be influenced by impurities. The most likely defects responsible for diffusion of Fe are iron interstitials and, for oxygen, oxygen vacancies, and the observed activation energies are discussed in terms of the properties of these defects. The diffusion data and defect models have been used to predict the rate of growth of Fe2O3 and indicate that outward Fe diffusion is the dominant transport process. Previously published data for Fe2O3 growth in a variety of experimental situations have been corrected to a single rate constant using a model for multilayer growth. The corrected data are all in good agreement but are approximately two orders of magnitude greater than predicted from diffusion data, which suggests that grain boundary diffusion controls the growth of Fe2O3 in practice. 相似文献
20.
M.I. KobetsK.G. Dergachev E.N. Khatsko S.L. GnatchenkoL.N. Bezmaternykh V.L. Temerov 《Physica B: Condensed Matter》2011,406(18):3430-3435
The AFMR spectra of the NdFe3(BO3)4 crystal are measured in a wide range of frequencies and temperatures. It is found that by the type of its magnetic anisotropy the compound is an “easy-plane” antiferromagnet with a weak anisotropy in the basal plane. The effective magnetic parameters are determined: anisotropy fields Ha1=1.14 kOe and Ha2=60 kOe and magnetic excitation gaps Δν1=101.9 GHz and Δν2=23.8 GHz. It is shown that commensurate-incommensurate phase transition causes a shift in resonance field and a considerable change in absorption line width.At temperatures below 4.2 K nonlinear regimes of AFMR excitation at low microwave power levels are observed. 相似文献