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1.
A series of Ni1−xCdxFe2O4 (0.0≤x≤0.8) were prepared by conventional double sintering ceramic method and sintered at 1200 °C for 6 h. X-ray diffraction results confirmed the single-phase spinel structures of all the samples. The Curie temperature decreases linearly with increasing Cd content, which is explained due to the weakening of the A–B exchange interaction. The sample with x=0.7 shows re-entrant type of spin glass phase transitions. The magnetic moment and saturation magnetization at 20 K are found to increase with Cd content up to x=0.5 and then tends to decrease for x>0.5. The increase in magnetic moment with cadmium is attributed to Neel's two sublattice (A- and B-sublattice) collinear models according to which the magnetic moment is the vector sum of the lattice magnetic moment. The decrease in magnetization for x>0.5 obeys the Yafet–Kittel (Y–K) model. The increase in Y–K angles for x>0.3 indicates the increased tendency for triangular spin arrangements on B-sites. This suggests the existence of a canted spin structure in the ferrite system with higher content of Cd.  相似文献   

2.
Magnetization and permeability of polycrystalline ferrites with general formula CdxMg1−xFe2−yCryO4 (x=0, 0.2, 0.4, 0.6, 0.8, 1.0; y=0, 0.05 and 0.10) were studied. Study of saturation magnetization reveals that the Neel's two-sublattice model exists upto x=0.4, for y=0, 0.05 and 0.1 and a three-sublattice model (YK-model) is predominant for x>0.4 and y=0, 0.05 and 0.10. The saturation magnetization and magnetic moment were found to decrease with the increase in Cr3+ contents, which is attributed to the dilution of B–B site interaction. Variation of initial permeability with temperature revealed the long-range ferromagnetic ordering in the compounds with x=0.4. The sample with x?0.4 and y=0, 0.05 and 0.10 showed peaking behavior near Curie temperature, which is attributed to the decrease of anisotropy constant K1 to zero. Low-frequency dispersion of initial permeability suggests domain wall displacement. Addition of Cd2+ resulted in a sharp decrease in Curie temperature. With the addition of Cr3+, initial permeability was found to decrease.  相似文献   

3.
The structural and magnetic properties of Mn-substituted lithium ferrites having the general formula Li0.5−0.5xMnxFe2.5−0.5xO4 (where x=0.0–1.0) prepared by the standard ceramic technique have been studied. Single phase cubic structure is confirmed by X-ray diffractometer. This result demonstrates that the samples are homogeneous, and the sharp peaks reveal that the samples are in crystalline form. The lattice parameter ‘a’ and average grain diameter ‘D’ increase with increasing Mn2+ ion substitution. The saturation magnetization and the experimental magnetic moment are found to increase with manganese up to x=0.5 and then tends to decrease for x>0.5. The increase in magnetic moment with manganese is attributed to Neel's two sublattice model according to which the magnetic moment is the vector sum of lattice magnetic moment. The decrease in magnetization for x>0.5 obeys the Yafet–Kittel (Y–K) model. The increase in Y–K angles for x≥0.5 indicates the increased favor for triangle spin arrangements on B-sites. This suggests the existence of canted spin structure in the ferrite system with higher content of Mn. Hystersis loops were measured. The initial permeability μi was measured as a function of temperature.  相似文献   

4.
The microstructure and magnetic properties have been investigated systematically for Sn1−xMnxO2 polycrystalline powder samples with x=0.02-0.08 synthesized by a solid-state reaction method. X-ray diffraction revealed that all samples are pure rutile-type tetragonal phase and the cell parameters a and c decrease monotonously with the increase in Mn content, which indicated that Mn ions substitute into the lattice of SnO2. Magnetic measurements revealed that all samples exhibit room temperature ferromagnetism. Furthermore, magnetic investigations demonstrate that magnetic properties strongly depend on doping content, x. The average magnetic moment per Mn atom decreases with increase in the Mn content, because antiferromagnetic super-exchange interaction takes place within the neighbor Mn3+ ions through O2− ions for the samples with higher Mn doping. Our results indicate that the ferromagnetic property is intrinsic to the SnO2 system and is not a result of any secondary magnetic phase or cluster formation.  相似文献   

5.
Polycrystalline Mg1−xZnxFe2O4 (x=0.0–0.6) ferrites have been prepared using solid-state reaction technique. The X-ray diffraction analysis revealed that the samples crystallize in a single-phase cubic spinel structure. The lattice parameter increases linearly with increase in zinc content obeying Vegard's law. The continuous decrease in Curie temperature (Tc) with an increase in Zn content is attributed to the weakening of A–B exchange interaction. Saturation magnetization (Ms) and magnetic moment are observed to increase up to x=0.4, and thereafter decrease due to the spin canting in B-sites. The initial permeability is found to increase with the addition of Zn2+ ions but the resonance frequency shifts towards the lower frequency.  相似文献   

6.
Sm-substituted barium hexaferrites, Ba3−xSmxCo2Fe24O41 (x=0-0.25), were prepared by a conventional ceramic sintering method. The microstructure, complex permittivity, complex permeability and static magnetic properties of the samples were studied using powder X-ray diffraction, field emission scanning electron microscopy, vector network analyzer and vibrating sample magnetometry. The results reveal that by introducing a relatively small amount of Sm3+ instead of Ba2+ an important modification of both structure and high-frequency electromagnetic properties can be obtained. Doping of Sm3+ suppressed the grain growth and gave rise to a decrease of the grain size. As the Sm content increases, the static magnetic properties continuously increase. The real part and imaginary part of complex permittivity initially increase with Sm content, and then decreases when x>0.10. The imaginary part of complex permeability decreases after Sm3+ is doped. There is no obvious change in the real part of the complex permeability for different Sm contents. The reasons are discussed using electromagnetic theory.  相似文献   

7.
Polycrystalline compositions of soft ferrite system, CdxCu1−xFe2−yGdyO4 (X=0.00, 0.20, 0.40, 0.60, 0.80 and 1.00; y=0.00, 0.10 and 0.30) were prepared by standard ceramic method. X-ray diffraction study show formation of single phase cubic spinel ferrite for the compositions X⩾0.20 and tetragonal nature for compositions X=0.00, for all values of Gd3+ (y=0.00, 0.10 and 0.30) concentration. Saturation magnetization and magnetic moments were found to be increasing with cadmium concentration up to X=0.40, for all values of Gd3+ content, obeying Neel's two sublattice model and decreases thereafter, showing existence of non-collinear spin interaction. The Gd3+ substitution results into reaction in the magnetic moments. This is due to occupancy of Gd3+ ion on octahedral (B) site, resulting into dilution in the magnetization of B sublattices. The Curie temperatures for all compositions are found to be decreasing with substitution of Cd2+ concentration. This is attributed to the occupancy of cadmium on tetrahedral (A) site, causing dilution in the inter site magnetic interaction. The temperature dependence of AC susceptibility is also studied and its behaviour is explained on the basis of domain structure.  相似文献   

8.
M-type hexagonal ferrite powder with partial substitution lr4++Co2+ has been synthesized by chemical-coprecipitation technique. The saturation magnetization Ms decreases linearly from 69.8 to 40.3 emu/g with increasing doping content from 0.5 to 1. The Coerecivity sharply drops for x=0.5, which can be explained by the decrease of the anisotropy constant K1 Curie temperature Tc decreases linearly with increasing ‘x’. Crystallographic studies were explained on the cation distribution consistent with Gorter spin model of parallel alignment.  相似文献   

9.
The crystal structure parameters and magnetic and electrical properties of La1?x CaxMnO3?x/2 reduced manganites with 0≤x≤0.5 are established. These investigations contribute to the understanding of magnetic interactions in manganites without Mn4+ ions. It is found that these manganites show a long-range antiferromagnetic order up to x=0.09 and transform into spin glasses at 0.09<x≤0.35. The compositions in the range 0.35<x≤0.5 show a strong increase in the spontaneous magnetization and critical point associated with the appearance of spontaneous magnetization and can therefore be viewed as inhomogenious ferromagnets. The magnetic and crystal structure peculiarities of La0.5Ca0.5MnO2.75 are established by the neutron diffraction method. The strongly reduced samples show a large magnetoresistance below the point where the spontaneous magnetization develops. The magnetic phase diagram of La1?x CaxMnO3?x/2 is established by magnetization measurements. The magnetic behavior is interpreted assuming that the Mn3+-O-Mn3+ magnetic interaction is anisotropic (positive-negative) in the orbitally ordered phase and isotropic (positive) in the orbitally disordered phase. Introduction of the oxygen vacancies changes the magnetic interaction sign from positive to negative, thereby leading to a spin glass state in strongly reduced compounds. The results obtained reveal unusual features of strongly reduced manganites such as a large ferromagnetic component, a high magnetic ordering temperature, and a large magnetoresistance despite the absence of Mn3+-Mn4+ pairs. In order to explain these results, the oxygen vacancies are supposed to be ordered.  相似文献   

10.
The effect of doping of rare earth Pr3+ ion as a replacement of Sm3+ in Sm0.5Sr0.5MnO3 is investigated. Temperature dependent dc and ac magnetic susceptibility, resistivity, magnetoresistance measurements on chemically synthesized (Sm0.5−xPrx)Sr0.5MnO3 show various unusual features with doping level x=0.15. The frequency independent ferromagnetic to paramagnetic transition at higher temperature (∼191 K) followed by a frequency dependent reentrant magnetic transition at lower temperature (∼31 K) has been observed. The nature of this frequency dependent reentrant magnetic transition is described by a critical slowing down model of spin glasses. From non-linear ac susceptibility measurements it has been confirmed that the finite size ferromagnetic clusters are formed as a consequence of intrinsic phase separation, and undergo spin glass-like freezing below a certain temperature. There is an unusual observation of a 2nd harmonic peak in the non-linear ac susceptibility around this reentrant magnetic transition at low temperature (∼31 K). Arrott plots at 10 and 30 K confirm the existence of glassy ferromagnetism below this low temperature reentrant transition. Electronic- and magneto-transport measurements show a strong magnetic field—temperature history dependence and strong irreversibility with respect to the sweeping of magnetic field. These results are attributed to the effect of phase separation and kinetic arrest of the electronic phase in this phase separated manganite at low temperatures.  相似文献   

11.
Polycrystalline Ni0.65−xCdxZn0.35Fe2O4 ferrites with x varying from 0.00 to 0.20 in steps of 0.04 have been prepared by conventional ceramic route. Calcination and sintering of samples were performed at 950 and 1250 °C for 4 and 2 h, respectively. The prepared samples were characterized by powder X-ray diffraction. The observed modifications in structure and increase in lattice constant are attributed to the difference in ionic radius of substituted Cd2+ ion and displaced Ni2+ ion. The room temperature specific saturation magnetization and Curie temperature are observed to decrease continuously with decrease in cadmium content and are attributed to the decline of A-B exchange interaction. The monotonic increase in initial permeability and decrease in magnetic loss are observed with cadmium concentration. An increase in dc electrical resistivity is observed up to x=0.12 of cadmium followed by a continuous decrease. The variation of electrical resistivity with temperature was measured in the temperature range of RT-140 °C and the corresponding activation energies for conduction obtained from the log ρ vs 1/T graphs.  相似文献   

12.
In this work we report the structure and magnetic properties of a series of single-phase indium-substituted yttrium iron garnet (In-YIG) nanoparticles with nominal composition of Y3InxFe5−xO12 (x=0.1, 0.2, 0.3 and 0.4) prepared by conventional mixed oxide route. Based on XRD results, the lattice parameters of the samples increased with increase in In3+ content due to its larger ionic radius. Mössbauer results confirmed the substitution of In3+ for Fe3+ in [a] site of YIG structure. Further, the magnitudes of the magnetic hyperfine field (MHF) were seen to reduce due to indium substitution. Moreover, a rising trend was observed for saturation magnetization (MS) of the samples with x>0.2 owing to the substitution of non-magnetic In3+ for Fe3+. However, the observed initial drop of MS for the sample with x=0.2 compared to that with x=0.1 is possibly attributed to the dominance of spin canting over the net magnetization rise caused by In3+ in [a] sites.  相似文献   

13.
The ferrite samples of a chemical formula Ni0.5−xMnxZn0.5Fe2O4 (where x=0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) were synthesized by sol-gel auto-combustion method. The synthesized samples were annealed at 600 °C for 4 h. An analysis of X-ray diffraction patterns reveals the formation of single phase cubic spinel structure. The lattice parameter increases linearly with increase in Mn content x. An initial increase followed by a subsequent decrease in saturation magnetization with increase in Mn content is observed showing inverse trend of coercivity (Hc). Curie temperature decreases with increase in Mn content x. The initial permeability is observed to increase with increase in Mn content up to x=0.3 followed by a decrease, the maximum value being 362. Possible explanation for the observed structural, magnetic, and changes of permeability behavior with various Mn content are discussed.  相似文献   

14.
The magnetic properties of Tb(Fe1−xCox)11.3Nb0.7 compounds with x=0, 0.05, 0.1, 0.15, 0.2 and 0.3 have been investigated. All compounds studied crystallize in the ThMn12-type of structure. Substitution of Co for Fe leads to a contraction of the unit-cell volume. The Curie temperature clearly increases with increasing Co content from 551 K for x=0 to 831 K for x=0.3. The magnetic moment of the transition-metal sublattice increases with increasing Co content from 22.2 μB/f.u. for x=0 to 23.1 μB/f.u. for x=0.3. As the temperature increases, a spin reorientation from easy-plane to easy-cone is found in all compounds investigated. The spin-reorientation temperatures Tsr have been derived from the temperature dependence of the magnetization in a low field and decrease monotonously with increasing Co content. The easy magnetization direction at room temperature has been determined by X-ray diffraction on magnetically-aligned powder samples. The influence of the substitution of Co for Fe on the magnetic anisotropy is discussed in terms of crystal-field theory.  相似文献   

15.
The effects of cubic crystal fields on the saturation magnetic moment of Sm3+ ion in ferromagnetic compounds have been investigated. In samarium compounds with magnetic elements, the exchange fieldH ex acting on Sm3+ ion is taken to be proportional to the sublattice magnetization of the magnetic element, while in compounds with nonmagnetic elementsH ex is taken to be proportional to the spin average of the Sm3+ ion and is determined self-consistently. In both types of compoundsH ex is assumed to be along [001] direction. The saturation magnetic moment is calculated by taking into account the admixture of excited (J=7/2 andJ=9/2) levels into the ground (J=5/2) level of Sm3+ ion by crystal fields and exchange fields. It is shown that depending upon the strength, the crystal fields quench or enhance the magnetic moment from the free ion value, and in some cases force Sm3+ ion to behave effectively like an (L+S) ion rather than an (LS)ion. The crystal fields may have important bearing on the performance of samarium compounds as permanent magnet materials.  相似文献   

16.
Structural, magnetic properties and magnetostriction studies of Sm1−xNdxFe1.55 (0≤x≤0.56) alloys have been performed. X-ray diffraction analysis confirms the presence of single cubic Laves phase in Sm1-xNdxFe1.55 alloys with 0≤x≤0.48. The lattice parameter of alloys increases linearly with increase in Nd content while the Curie temperature behaves in the opposite way. The alloy x=0.08 exhibits a giant magnetostriction value (λ-λ) of −2187 ppm at a magnetic field of 12 kOe due to the anisotropy compensation between Sm3+ and Nd3+ ions.  相似文献   

17.
Samples of stoichiometry (AgI)4(PbI2)1?x (CdI2) x , (0 ≤ x ≤ 0.4), have been prepared and studied by electrical conductivity, X-ray powder diffraction and DSC techniques. The ionic conductivity of samples was found to increase with temperature, and an abrupt increase at phase transition temperature was observed. The Cd+2-doped samples exhibited lower phase transition temperature compared to that of the pure samples. The ionic conductivity decreases with an increase in Cd+2 content in pre-transition, while enhances in conductivity result in Cd+2 content samples of x ≤ 0.2 in the post-transition region. Different resources of investigation confirmed the solubility limit of Cd+2 in the high-temperature phase to be x = 0.2. The change in the ionic conductivity of Cd+2-doped samples is explained by the increase in the defect concentration and the free volume available in the lattice. The drop in phase transition temperature of Cd2+-doped systems is attributed to the lattice distortion and the increase in the defect–defect interaction.  相似文献   

18.
We performed the magnetization measurement on Ho1−xDyxNi2B2C single crystals (x=0.1, 0.2, 0.3, 0.4, and 0.6) with magnetic field applied perpendicular and parallel to the c-axis. But only for the magnetic field perpendicular to the c-axis, the increase of Dy3+ concentration affects the magnetically ordered states of HoNi2B2C compound and makes the phase diagram more complicated. The antiferromagnetic ordering state attributed to Dy3+ sublattice starts to appear from a case of x=0.2 and finally the magnetic phase diagram becomes analogous to that of DyNi2B2C as x is increased which is consistent with the neutron scattering result.  相似文献   

19.
We report the effect of intense laser field on donor impurities in a semimagnetic Cd1-xinMnxinTe/Cd1-xoutMnxoutTe quantum dot. The spin polaronic energy of different Mn2+ is evaluated for different dot radii using a mean field theory in the presence of laser field. Magnetization is calculated for various concentrations of Mn2+ ions with different dot sizes. Significant magnetization of Mn spins can be obtained through the formation of polarized exciton magnetic polarons (EMPs). A rapid decrease of the laser dressed donor ionization energy for different values of dot sizes with increasing field intensity is predicted. Also, it is found that the polarization of EMPs increases rapidly at higher excitation energies.  相似文献   

20.
The high-temperature oxidation resistance and magnetic properties of Si-doped Sm2Co17-type magnets at 500 °C were systematically investigated. The Sm(Co0.76, Fe0.1, Cu0.1, Zr0.04)7Six (x=0–0.6) magnets were prepared by the conventional powder metallurgical technique. It is found that the addition of silicon in the Sm2Co17-type magnet can remarkably improve its oxidation resistance. Moreover, a small amount of silicon addition can also increase its high-temperature intrinsic coercivity. A maximum intrinsic coercivity of 6.7 kOe at 500 °C was obtained for the Sm2Co17-type magnet with Si content x=0.4, whose high-temperature maximum energy product loss was about 2.5 times smaller than pure Sm2Co17-type magnet after oxidation at 500 °C for 100 h, indicating the enhanced oxidation resistance. Its corresponding Curie temperature and saturation magnetization are about 723.9 °C and 7.4 kG, respectively.  相似文献   

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