共查询到20条相似文献,搜索用时 25 毫秒
1.
Bi doped lanthanum manganites with the chemical composition of La0.67−xBixCa0.33MnO3 (x=0, 0.05, 0.1, 0.2) were prepared by the standard solid-state process. The Curie temperatures were measured to be 267 K for x=0, 248 K for x=0.05, 244 K for x=0.1 and 229 K for x=0.2 samples. It was found that the maximum value of the magnetic entropy change ∣ΔSm∣ has reached the highest value of 6.08 J/kg K at 3 T for the composition with x=0.05. Nearly the same maximum entropy change was observed for the x=0 sample. A large decrease in the magnitude of the entropy change was observed for the x=0.2 sample. 相似文献
2.
Effects of Ag addition on electrical transport and magnetic properties of La0.67Ba0.33Mn0.88Cr0.12O3
Xiao-Bo Yuan Yi-Hua LiuNa Yin Cheng-Jian WangLiang-Mo Mei 《Journal of magnetism and magnetic materials》2006
We have prepared a series of polycrystalline manganites with the nominal compositions, La0.67Ba0.33Mn0.88Cr0.12O3/Agx (LBMCO/Agx) (x is the mole fraction) with x=0, 0.05, 0.1, 0.15, 0.2, 0.23, 0.27, 0.3, 0.35. The X-ray diffraction patterns show that the samples with x>0.05 are two-phase composites. The Ag addition in LBMCO improves the properties of grain surfaces/boundaries and reduces the resistivity of the composites. For x=0.30 sample, a minimum resistivity is obtained and a maximum room temperature magnetoresistance up to −54.5% was observed at 288 K, 1 T field. The room temperature TC and the reduced resistivity are responsible for the enhancement of room temperature MR. 相似文献
3.
Enyao Zhang Yungui ChenTiebang Zhang Yongbai TangMingjing Tu 《Journal of magnetism and magnetic materials》2006
The crystal structure and magnetocaloric effect of Gd5SixSn4−x (with x=2.4, 2.6 and 2.8) alloys were studied by means of X-ray power diffraction (XRD) and magnetic measurements. From the XRD results, these alloys adopt a Gd5Si4-type structure for x=2.8, Gd5Si4-type and Gd5Si2Ge2-type mixed structures for x=2.4 and 2.6, while some minor phases can also be found. The Curie temperatures of the Gd5SixSn4−x increases gradually when x increases from 276 K for x=2.4, to 301.5 K for x=2.8. Magnetic entropy changes of these alloys at a magnetic field change of 0–1.8 T are 1.88, 2.26 and 1.69 J/kg K for x=2.4, 2.6 and 2.8, respectively. The temperature-dependent XRD analysis shows that there is no crystallographic transition for these alloys, which can explain their low magnetic entropy changes. 相似文献
4.
Yanhong Ding Tian QiuXuan Liu Yi LongYongqin Chang Rongchang Ye 《Journal of magnetism and magnetic materials》2006
Under various amplitude of AC magnetic fields domain wall motion is the main mechanism in the magnetization process. This includes domain wall bulging and domain wall displacing. In this paper complex permeability-frequency spectra of (Fe1−xCox)73.5Cu1Nb3Si13.5B9 (x=0,0.5) nanocrystalline alloys were measured as a function of the AC magnetic field, ranging from 0.001 to 0.04 Oe. Obvious changes have been found in complex permeability spectra for alloy x=0 with the change of the amplitude of AC magnetic field, but variation of AC magnetic field has little effect on complex permeability spectra for alloy x=0.5. This is attributed to the increased pinning field after substitution of Fe with Co in Fe73.5Cu1Nb3Si13.5B9 nanaocrystalline alloy. 相似文献
5.
G. Narsinga Rao Saibal Roy Chung-Yuan Mou J.W. Chen 《Journal of magnetism and magnetic materials》2006
We have investigated the magnetotransport and magnetic properties on polycrystalline samples of Sr2−xLaxFeMoO6 (x=0, 0.2, 0.4, 0.6, 0.8 and 1.0). The magnitude of intergrain tunneling magnetoresistance with low magnetic field of 0.88 T for x=0.2 and 0.4 samples are as large as 5% and 7% at room temperature and 13% and 10% at 10 K, respectively. The increase of coercivity (Hc), ratio of remanent magnetization with respect to saturation magnetization (Mr/Ms), high saturation fields, and reduction of the saturation magnetization indicate that random disorder of spin orientation is mainly responsible for enhancement of the low-field magnetoresistance for samples with x?0.4. Whereas rapid drop of Hc, Mr/Ms, Mr, and saturation fields for samples with x>0.4 signifies the growth of antiphase boundary, which gives rise to lower values of low-field MR. 相似文献
6.
Shiyue Xu Minjian Zhong Liming YuHangde Chen Zhengming HeJincang Zhang 《Journal of magnetism and magnetic materials》2006
FCC (Fe55Ni45)1−xCx supersaturated solid solution was prepared in a wide concentration range (0?x?0.9) by mechanical alloying of nanocrystalline Fe55Ni45 with graphite. The lattice constant of Fe55Ni45 increases linearly with increasing carbon content up to x=0.25. At the same time, it is found that the magnetic moment per metal atom (Fe, Ni) decreases linearly with increasing carbon content for 0?x?0.25 with a slope of 1.2 μB/at. For high carbon content, x?0.5, it is observed that the decrease of lattice constant and increase of moment per metal atom (Fe, Ni) with increasing C content, indicates that the dissolution of carbon is hindered by the high-volume fraction of graphite in the initial powder mixture. The complete amorphization of x=0.5 does not occur after the extended ball milling. The alloying effect of carbon on the magnetization is compared with other metalloid B, P, and Si in Fe- and Ni-based binary system. 相似文献
7.
We have studied the anisotropic two-dimensional nearest-neighbor Ising model with competitive interactions in both uniform longitudinal field H and transverse magnetic field Ω. Using the effective-field theory (EFT) with correlation in cluster with N=1 spin we calculate the thermodynamic properties as a function of temperature with values H and Ω fixed. The model consists of ferromagnetic interaction Jx in the x direction and antiferromagnetic interaction Jy in the y direction, and it is found that for H/Jy∈[0,2] the system exhibits a second-order phase transition. The thermodynamic properties are obtained for the particular case of λ=Jx/Jy=1 (isotropic square lattice). 相似文献
8.
The linear and nonlinear AC susceptibility as a function of temperature were measured on LaMn1−xCuxO3 compounds for x=0.05–0.30. Samples with x?0.10 exhibit paramagnetic to ferromagnetic transitions followed by low temperature spin glass like transition. The linear susceptibility exhibits strong frequency dependence and is analyzed in terms of standard theoretical model for spin glass. The magnitude and peak temperature of nonlinear susceptibility vary with AC field amplitudes. They are analyzed in terms of critical behaviour in the vicinity of spin glass transition temperature and the critical exponent is found to be 3.2. 相似文献
9.
Ligia E. Zamora G.A. Pérez Alcázar C. González J.M. Greneche W.R. Aguirre A. Bohórquez E.M. Baggio Saitovich D. Sánchez 《Journal of magnetism and magnetic materials》2006
Melted alloys of the FexMn0.65−xAl0.35 disordered system, 0.25?x?0.65, were experimentally studied by Mössbauer spectrometry, vibrating sample magnetometry and AC magnetic susceptibility. All the alloys exhibit the BCC structure with a nearly constant lattice parameter (2.92 Å). Mössbauer studies at room temperature (RT) show that in the 0.25 ?x?0.45 range the alloys are paramagnetic (P) while in the 0.50?x?0.65 range, they are ferromagnetic. At 77 K, Mössbauer studies show that the alloy with x=0.25 presents weak magnetic character that is consistent with an antiferromagnetic (AF) behavior due to the high Mn content, while those with 0.30?x?0.40 are paramagnetic, and those in the 0.45?x ?0.65 range are ferromagnetic (F) with a mean field increasing with the Fe content. Hysteresis cycles at RT prove the paramagnetic character of the alloys between x=0.25 and 0.40 and the ferromagnetic character for x?0.45. Complementary measurements using AC magnetic susceptibility permit a magnetic phase diagram to be proposed, with the P phase for high temperature and all the compositions, the AF phase for low Fe content and at low temperature, the F phase for high Fe content above RT and the spin glass phase for all the compositions and at temperatures lower than 46 K. In addition, the mean field renormalization group (MFRG) method, applied to a random competitive and site dilute Ising model with nearest-neighbor, gives rise to magnetic phase diagram, which fairly agrees with previous experimental one. 相似文献
10.
11.
Mg0.7Zn0.3SmxFe2−xO4 ferrites were prepared by the solid-state reaction method and were characterized by X-ray diffraction and magnetization measurements. A single spinel phase was obtained in the range 0.00?x?0.03. The lattice parameter was found to increase at x=0.01 and then decreases up to x=0.03, which may indicate a distortion in the spinel lattice. The saturation magnetization was found to decrease with the increase in x up to 0.04, due to the replacement of the Fe3+ ions by the Sm3+ ions. 相似文献
12.
Sang Soo Yu Ki Hak Kim Young Eon Ihm Dojin Kim Hyojin Kim Soon Ku Hong Chang Soo Kim Hyun Ryu Sangjun Oh 《Journal of magnetism and magnetic materials》2006
Si1−xMnx (x?0.22) thin films were grown by using a thermal evaporator, and their magnetic and electrical properties were investigated. The Si1−xMnx semiconductors are amorphous when Mn concentration is 9.0 at% and less. The electrical resistivities of amorphous Si1−xMnx (x?0.09) semiconductor thin films are in the range of 9.86–6.59×10−4 Ω cm at room temperature and decrease with increasing Mn concentration. The amorphous Si1−xMnx (x?0.09) semiconductor thin films are p-type and hole densities are 3.73×1018–1.33×1022 cm−3 at room temperature. Low temperature magnetization characteristics reveal that amorphous Si1−xMnx (x?0.09) semiconductor thin films are paramagnetic. 相似文献
13.
Matching for a wavefunction the WKB expansion at large distances and Taylor expansion at small distances leads to a compact, few-parametric uniform approximation found in Turbiner and Olivares-Pilon (2011). The ten low-lying eigenstates of H2+ of the quantum numbers (n,m,Λ,±) with n=m=0 at Λ=0,1,2, with n=1, m=0 and n=0, m=1 at Λ=0 of both parities are explored for all interproton distances R. For all these states this approximation provides the relative accuracy ?10−5 (not less than 5 s.d.) locally, for any real coordinate x in eigenfunctions, when for total energy E(R) it gives 10-11 s.d. for R∈[0,50] a.u. Corrections to the approximation are evaluated in the specially-designed, convergent perturbation theory. Separation constants are found with not less than 8 s.d. The oscillator strength for the electric dipole transitions E1 is calculated with not less than 6 s.d. A dramatic dip in the E1 oscillator strength f1sσg−3pσu at R∼Req is observed. The magnetic dipole and electric quadrupole transitions are calculated for the first time with not less than 6 s.d. in oscillator strength. For two lowest states (0,0,0,±) (or, equivalently, 1sσg and 2pσu states) the potential curves are checked and confirmed in the Lagrange mesh method within 12 s.d. Based on them the Energy Gap between 1sσg and 2pσu potential curves is approximated with modified Pade Re−R[Pade(8/7)](R) with not less than 4-5 figures at R∈[0,40] a.u. Sum of potential curves E1sσg+E2pσu is approximated by Pade 1/R[Pade(5/8)](R) in R∈[0,40] a.u. with not less than 3-4 figures. 相似文献
14.
We discuss three Hamiltonians, each with a central-field part H0 and a PT-symmetric perturbation igz. When H0 is the isotropic Harmonic oscillator the spectrum is real for all g because H is isospectral to H0+g2/2. When H0 is the Hydrogen atom then infinitely many eigenvalues are complex for all g. If the potential in H0 is linear in the radial variable r then the spectrum of H exhibits real eigenvalues for 0<g<gc and a PT phase transition at gc. 相似文献
15.
Denise A. do Nascimento Minos A. Neto J. Ricardo de Sousa Josefa T. Pacobahyba 《Journal of magnetism and magnetic materials》2012
In this paper we study the critical behavior of a two-sublattice Ising model on an anisotropic square lattice in both uniform longitudinal (H ) and transverse (Ω) fields by using the effective-field theory. The model consists of ferromagnetic interaction Jx in the x direction and antiferromagnetic interaction Jy in the y direction in the presence of the H and Ω fields. We obtain the phase diagrams in the H–T and Ω–T planes changing values of the Ω and H parameters, respectively for fixed value at λ=Jx/Jy=1. At null temperature, the ground state phase diagram in the Ω–H plane for several values of λ parameter is analyzed. In the particular case of λ=1 we compare our results with mean-field theory (MFT) and was not observed reentrant behavior around of the critical field Hc/Jy=2.0 for Ω=0 by using EFT. 相似文献
16.
L.M. Wang Jyh-Yi Lee H.C. Yang J.C. Chen Hsiang-Lin Liu Kun-Sheng Lu Lance Horng H.E. Horng 《Journal of magnetism and magnetic materials》2006
La0.7Sr0.3MnO3 (LSMO) tunneling magnetoresistance (TMR) junctions have been fabricated on step-edge (0 0 1) SrTiO3 substrates with a high step-edge angle. In the measurement of magnetoresistance (MR) ratio versus external magnetic field H, butterfly-like MR curves are clearly observed. The MR(H ) curves vary with θ, the angle between the applied magnetic field and the current direction in the substrate plane, showing anisotropic MR properties. A much broader MR(H) response is observed for the configuration of H perpendicular to the substrate plane. Additionally, the maxima-MR field Hp almost coincides with the coercive field Hc for θ<60° but obeys a different form from Hc(θ). The high-field junction resistance shows an intrinsic sin2θ angular dependence, while the low-field resistance shows an extrinsic cos(4θ) angular dependence. The distinctive features are mainly due to the induced magnetization anisotropy in the artificial steps of grain boundaries. 相似文献
17.
Kwang Joo Kim Hee Kyung Kim Young Ran Park Geun Young Ahn Chul Sung Kim Jae Yun Park 《Journal of magnetism and magnetic materials》2006,300(2):300-305
Magnetic and optical properties of FexCo3−xO4 thin films grown by sol–gel method have been investigated as the Fe composition (x ) increases from 0 to 2. X-ray diffraction measurements revealed that the normal- and inverse-spinel phases coexist for 0.76?x?0.93. The normal-spinel phase is dominant below x=0.76 while the inverse-spinel phase above x=0.93. The lattice constant of the inverse-spinel phase is found to be larger than that of the normal-spinel phase. For both phases the lattice constant increases with increasing x. The FexCo3−xO4 films containing the inverse-spinel phase exhibit net magnetization that increases with increasing x . Conversion electron Mössbauer spectrum measured on the x=0.93 sample showed that Fe2+ ions prefer the octahedral sites, indicating the formation of the inverse-spinel phase. Analysis on the measured optical absorption spectra for the samples by spectroscopic ellipsometry indicates a dominance of the normal-spinel phase for low x in which Fe3+ ions mostly occupy the octahedral sites. Observation of a crystal-field transition at 1.6 eV originating from tetrahedral Fe3+ ion confirms the existence of the inverse-spinel phase for high x. 相似文献
18.
CoFe2O4 nanoparticles with a cubic spinel structure are prepared by a high-temperature thermal decomposition method. The average particle sizes are 4.6 and 5.7 nm for CoFe2O4 made with two kinds of solvents by TEM. Mössbauer spectra of 4.6 nm particles displayed a superparamagnetic behavior as demonstrated by a single line with zero hyperfine fields, but that of 5.7 nm particles did not at room temperature. It is considered that anisotropy energy was still more superior to thermal energy because of particle size of 5.7 nm CoFe2O4. Furthermore, Mössbauer spectra exhibited the typical spectrum shapes of the CoFe2O4 at 4.2 K. The spectrum at 4.2 K was fitted using two magnetic components of hyperfine fields Hhf=540.4,512.6 kOe and isomer shifts δ=0.40,0.30 mm/s for 4.6 nm and Hhf=542.7,512.8 kOe and δ=0.41,0.29 mm/s for 5.7 nm corresponding to Fe3+ ions at site A and site B, respectively. 相似文献
19.
Kenichi Katoh Masafumi Maeda Saori Matsuda Akira Ochiai 《Journal of magnetism and magnetic materials》2012
The magnetic and transport properties of single-crystal Yb3Cu4Ge4 with the Gd3Cu4Ge4-type orthorhombic structure are presented. Magnetization along the b-axis at 2 K saturates to 2.8μB/Yb at 3 kOe, while that along the a- and c-axes at 2 K are gradually increasing to the value of 1.5μB/Yb and 0.39μB/Yb at 50 kOe, respectively. The electrical resistivity within the ab-plane shows a metallic behavior in contrast to a broad maximum at around 30 K for that along the c-axis. Each resistivity for the principal axis suddenly decreases below 8 K. The specific heat shows a λ-type sharp peak at 7.8 K. The electronic specific heat coefficient is estimated to be 29.4 mJ/mol Yb K2 by fitting the magnetic part of the specific heat below 3 K. The magnetic entropy released up to TC is 68% of that of R ln 2, expected for the doublet ground state. It is revealed that Yb3Cu4Ge4 is categorized to a weak heavy-fermion system showing a ferromagnetic transition at 7.8 K with uniaxial anisotropy along the b-axis. 相似文献
20.
We discuss space-time symmetric Hamiltonian operators of the form H=H0+igH′, where H0 is Hermitian and g real. H0 is invariant under the unitary operations of a point group G while H′ is invariant under transformation by elements of a subgroup G′ of G. If G exhibits irreducible representations of dimension greater than unity, then it is possible that H has complex eigenvalues for sufficiently small nonzero values of g. In the particular case that H is parity-time symmetric then it appears to exhibit real eigenvalues for all 0<g<gc, where gc is the exceptional point closest to the origin. Point-group symmetry and perturbation theory enable one to predict whether H may exhibit real or complex eigenvalues for g>0. We illustrate the main theoretical results and conclusions of this paper by means of two- and three-dimensional Hamiltonians exhibiting a variety of different point-group symmetries. 相似文献