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1.
Bi doped lanthanum manganites with the chemical composition of La0.67−xBixCa0.33MnO3 (x=0x=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=0x=0, 248 K for x=0.05x=0.05, 244 K for x=0.1x=0.1 and 229 K for x=0.2x=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=0.05x=0.05. Nearly the same maximum entropy change was observed for the x=0x=0 sample. A large decrease in the magnitude of the entropy change was observed for the x=0.2x=0.2 sample.  相似文献   

2.
The ferrite compositions of (Ni0.25−xMgxCu0.2Zn0.55)Fe2O4 with x=0.0x=0.0, 0.07, 0.13, 0.18, and 0.25 were synthesized through nitrate-citrate auto-combustion method. The as-burnt powders showed the presence of crystalline cubic spinel ferrite with about 19–22 nm crystallite sizes. The resultant powders were calcined at 700 °C/2 h and pressed ferrites were sintered at 950 °C/4 h. The initial permeability, magnetic loss and AC resistivity were measured in the frequency range 10 Hz–10 MHz. The permeability and AC resistivity were found to increase and the magnetic loss decreased with Mg substitution for Ni, up to x=0.18x=0.18. The very high permeability in the composition x=0.18x=0.18, was due to better densification, lower magnetostriction constant and inner stresses, etc. The AC resistivity of the composition was also highest. The composition would be better than NiCuZn-based material for more miniaturization of multi layer chip inductor.  相似文献   

3.
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?0.030.00?x?0.03. The lattice parameter was found to increase at x=0.01x=0.01 and then decreases up to x=0.03x=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   

4.
FCC (Fe55Ni45)1−xCx   supersaturated solid solution was prepared in a wide concentration range (0?x?0.9)(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=0.25x=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?0.250?x?0.25 with a slope of 1.2 μB/at. For high carbon content, x?0.5x?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=0.5x=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   

5.
The crystal structure and magnetocaloric effect of Gd5SixSn4−x   (with x=2.4x=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=2.8x=2.8, Gd5Si4-type and Gd5Si2Ge2-type mixed structures for x=2.4x=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=2.4x=2.4, to 301.5 K for x=2.8x=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=2.4x=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   

6.
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=0,0.5x=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=0x=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=0.5x=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   

7.
We have found that the initial permeability μμ of Co2ZCo2Z ferrite is improved by the substitution of Ti4+Ti4+ and Zn2+Zn2+ ions for Fe3+Fe3+ ions. The substituted sample of Ba3Co2TixZnxFe24-2xO41Ba3Co2TixZnxFe24-2xO41 with x=0.85x=0.85 has a maximum μμ of 24, which is twice as large as that of the non-substituted sample with x=0x=0. The particle size and shape are changed by the substitution. This is influential in the densification and the preferential orientation of a toroidal-shape sample, which results in the improvement of μμ.  相似文献   

8.
Si1−xMnx   (x?0.22x?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?0.09x?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?0.09x?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?0.09x?0.09) semiconductor thin films are paramagnetic.  相似文献   

9.
We have investigated the magnetotransport and magnetic properties on polycrystalline samples of Sr2−xLaxFeMoO6 (x=0x=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=0.2x=0.2 and 0.40.4 samples are as large as 5% and 7% at room temperature and 13% and 10% at 10 K, respectively. The increase of coercivity (HcHc), ratio of remanent magnetization with respect to saturation magnetization (Mr/MsMr/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?0.4x?0.4. Whereas rapid drop of HcHc, Mr/MsMr/Ms, MrMr, and saturation fields for samples with x>0.4x>0.4 signifies the growth of antiphase boundary, which gives rise to lower values of low-field MR.  相似文献   

10.
The grand partition functions Z(T,B)Z(T,B) of the Ising model on L×LL×L triangular lattices with fully periodic boundary conditions, as a function of temperature T and magnetic field B  , are evaluated exactly for L<12L<12 (using microcanonical transfer matrix) and approximately for L?12L?12 (using Wang–Landau Monte Carlo algorithm). From Z(T,B)Z(T,B), the distributions of the partition function zeros of the triangular-lattice Ising model in the complex temperature plane for real B≠0B0 are obtained and discussed for the first time. The critical points aN(x)aN(x) and the thermal scaling exponents yt(x)yt(x) of the triangular-lattice Ising antiferromagnet, for various values of x=e−2βBx=e2βB, are estimated using the partition function zeros.  相似文献   

11.
Multiferroic ground states with a spatially modulated antiferromagnetic structure and electric polarization have been revealed in Eu1−xYxMnO3 (0.2?x?0.50.2?x?0.5) single crystals. While the slightly substituted (x?0.1x?0.1) compounds exhibited a transition from the incommensurate (IC) to the canted antiferromagnetic (CAF) state at TCA<TNTCA<TN, the transitions from IC to commensurate ferroelectric (C/FE) phase were observed at Tlock<TNTlock<TN for x>0.2x>0.2. Various phase transitions were observed in the magnetic fields up to 250 kOe along a, b, c axes by magnetization, magnetostriction and electric polarization measurements which show an existence of a spontaneous electric polarization below Tlock.  相似文献   

12.
We have studied the anisotropic two-dimensional nearest-neighbor Ising model with competitive interactions in both uniform longitudinal field HH and transverse magnetic field ΩΩ. Using the effective-field theory (EFT) with correlation in cluster with N=1N=1 spin we calculate the thermodynamic properties as a function of temperature with values HH and ΩΩ fixed. The model consists of ferromagnetic interaction JxJx in the xx direction and antiferromagnetic interaction JyJy in the yy direction, and it is found that for H/Jy∈[0,2]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=1λ=Jx/Jy=1 (isotropic square lattice).  相似文献   

13.
The magnetic, transport, and optical properties of electron-doped Ca1−xLaxMnO3−δ single crystals with x  ?0.12 were studied. The magnetic measurements show that in single crystals with x=0x=0 and 0.05 the G-type AFM phase with weak FM component is realized and in crystals with x=0.10x=0.10 and 0.12 the G- and C-type AFM phases coexist. The C-type magnetic structure arises at less concentration of La than in polycrystalline samples as a result of oxygen vacancies being additional source of electrons. Under magnetic transitions in the G- and C-type phases, resistivity and magnetoresistance of the doped single crystals have anomalies. Optical absorption in IR range indicates formation of a charge gap in crystals with x=0.10x=0.10 and 0.12 at appearance of the C-AFM and monoclinic phase with orbital/charge ordering. By comparing optical and transport properties, heterogeneous electronic state and its relation with heterogeneous magnetic state are shown.  相似文献   

14.
The structural and magnetic properties of Nd1−xTbxFe10.5Mo1.5 (x=0x=0, 0.2, 0.4, 0.6, 0.8, 1.0) compounds have been investigated by means of X-ray diffraction and magnetic measurements. All the investigated compounds crystallize in the tetragonal ThMn12-type structure with I4/mmm space group. The lattice parameters a, c and the unit-cell volume V decrease with increasing x. The Curie temperatures TC are almost independent x. There exists a unique spin-reorientation transition for the end compositions of Nd1−xTbxFe10.5Mo1.5 compounds with x=0x=0 and x=1x=1, while two spin-reorientation transitions are observed for x=0.2–0.8x=0.20.8. The room-temperature magnetocrystalline anisotropy of Nd1−xTbxFe10.5Mo1.5 compounds changes from uniaxial to planar with increasing x content. Based on magnetic measurements, a magnetic phase diagram of Nd1−xTbxFe10.5Mo1.5 compounds is constructed. By minimizing the magnetocrystalline anisotropy energy, a theoretical magnetic phase diagram for the Nd1−xTbxFe10.5Mo1.5 system is derived, showing a reasonable agreement with the observations.  相似文献   

15.
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,±)(n,m,Λ,±)  with n=m=0n=m=0 at Λ=0,1,2Λ=0,1,2, with n=1n=1, m=0m=0 and n=0n=0, m=1m=1 at Λ=0Λ=0 of both parities are explored for all interproton distances RR. For all these states this approximation provides the relative accuracy ?10−5?105 (not less than 5 s.d.) locally, for any real coordinate xx in eigenfunctions, when for total energy E(R)E(R) it gives 10-11 s.d. for R∈[0,50]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 E1E1 is calculated with not less than 6 s.d. A dramatic dip in the E1E1 oscillator strength f1sσg−3pσuf1sσg3pσu at R∼ReqRReq 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,±)(0,0,0,±) (or, equivalently, 1sσg1sσg and 2pσu2pσu states) the potential curves are checked and confirmed in the Lagrange mesh method within 12 s.d. Based on them the Energy Gap between 1sσg1sσg and 2pσu2pσu potential curves is approximated with modified Pade Re−R[Pade(8/7)](R)ReR[Pade(8/7)](R) with not less than 4-5 figures at R∈[0,40]R[0,40] a.u. Sum of potential curves E1sσg+E2pσuE1sσg+E2pσu is approximated by Pade 1/R[Pade(5/8)](R)1/R[Pade(5/8)](R) in R∈[0,40]R[0,40] a.u. with not less than 3-4 figures.  相似文献   

16.
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 (ΩΩ) 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 ΩΩ fields. We obtain the phase diagrams in the H–THT and Ω–TΩT planes changing values of the ΩΩ and H   parameters, respectively for fixed value at λ=Jx/Jy=1λ=Jx/Jy=1. At null temperature, the ground state phase diagram in the Ω–HΩH plane for several values of λλ parameter is analyzed. In the particular case of λ=1λ=1 we compare our results with mean-field theory (MFT) and was not observed reentrant behavior around of the critical field Hc/Jy=2.0Hc/Jy=2.0 for Ω=0Ω=0 by using EFT.  相似文献   

17.
We discuss three Hamiltonians, each with a central-field part H0H0 and a PT-symmetric perturbation igzigz. When H0H0 is the isotropic Harmonic oscillator the spectrum is real for all gg because HH is isospectral to H0+g2/2H0+g2/2. When H0H0 is the Hydrogen atom then infinitely many eigenvalues are complex for all gg. If the potential in H0H0 is linear in the radial variable rr then the spectrum of HH exhibits real eigenvalues for 0<g<gc0<g<gc and a PT phase transition at gcgc.  相似文献   

18.
The large-n expansion is applied to the calculation of thermal critical exponents describing the critical behavior of spatially anisotropic d-dimensional systems at m  -axial Lifshitz points. We derive the leading non-trivial 1/n1/n correction for the perpendicular correlation-length exponent νL2νL2 and hence several related thermal exponents to order O(1/n)O(1/n). The results are consistent with known large-n expansions for d  -dimensional critical points and isotropic Lifshitz points, as well as with the second-order epsilon expansion about the upper critical dimension d?=4+m/2d?=4+m/2 for generic m∈[0,d]m[0,d]. Analytical results are given for the special case d=4d=4, m=1m=1. For uniaxial Lifshitz points in three dimensions, 1/n1/n coefficients are calculated numerically. The estimates of critical exponents at d=3d=3, m=1m=1 and n=3n=3 are discussed.  相似文献   

19.
We discuss space-time symmetric Hamiltonian operators of the form H=H0+igHH=H0+igH, where H0H0 is Hermitian and gg real. H0H0 is invariant under the unitary operations of a point group GG while HH is invariant under transformation by elements of a subgroup GG of GG. If GG exhibits irreducible representations of dimension greater than unity, then it is possible that HH has complex eigenvalues for sufficiently small nonzero values of gg. In the particular case that HH is parity-time symmetric then it appears to exhibit real eigenvalues for all 0<g<gc0<g<gc, where gcgc is the exceptional point closest to the origin. Point-group symmetry and perturbation theory enable one to predict whether HH may exhibit real or complex eigenvalues for g>0g>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   

20.
The effect of Gd substitution in M-type strontium hexaferrites has been examined in two series of samples, (Sr1-xGdx)O·5.25(Sr1-xGdx)O·5.25Fe2O3Fe2O3 and Sr1-xGdxFe12-xCoxO19Sr1-xGdxFe12-xCoxO19, both prepared by the ceramic method, where x=0–0.40x=00.40. The samples have been characterized by XRD, VSM and SEM-EDAX techniques. All substituted samples present primarily the hexaferrite structure. Sample (Sr0.95Gdx0.05)O·5.25(Sr0.95Gdx0.05)O·5.25Fe2O3Fe2O3 is single phase. Formation of impurity phases is affected by stoichiometry and presence of Co. In Sr–Gd samples, coercivity showed a maximum value of 305 kA/m (3.8 kOe) for x=0.20x=0.20, while remanence and saturation magnetization did not decrease. Coercivity and magnetization in the Sr–Gd–Co series decreased steadily with substitution degree.  相似文献   

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