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1.
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
2.
Torque measurements have been performed at 4 and 77 K on single crystals of Mn1?xFe2+xO4 (0<x<0.05) and MnFe2?xTixO4 (0<x<0.1). The crystals were either quenched or slowly cooled causing a change of inversion by 0.1. It is found that the magnetic anisotropy due to the ferrous ions in the Ti-doped samples is 80 per cent larger than in the Mn1?xFe2+xO4 crystals. In both crystal series the ferrous ion anisotropy in the slowly cooled crystals is 70 per cent higher than in the quenched crystals. The K1 of MnFe2O4 at 4 K is found to decrease from ?3.6 × 105 erg/cm3 after show cooling, down to ?2.6 × 105 erg/cm3 after quenching. 相似文献
3.
K.V. PocholokB.I. Pocrovskii A.M. BabeshkinA.K. Gapeev L.N. Komissarova 《Solid State Communications》1971
MnFe2−xScxO4 was studied by means of the Mössbauer effect. It was shown that Sc replaces Fe in octahedral sites only. Sc substitution results in the change of cationic distribution of a normal in the ferrite lattice. For the MnFe1,3Sc0,7O4 sample the cationic distribution of a normal spinel was found. 相似文献
4.
We report the effects of heat treatment on Zn x Ni1???x Fe2O4 (x?= 0, 0.5 and 1.0) and MnFe2O4 ferrite nanoparticles. The as-prepared compounds were sintered from 400°C to 1100°C. Pure ZnFe2O4 (x?= 1.0) and MnFe2O4 could be obtained under low reaction temperature of 200°C. NiFe2O4 (x?= 0) and Zn0.5Ni0.5Fe2O4 (x?= 0.5) nanoferrites crystallized with single phase cubic spinel structure after annealing at 600°C. The single phase cubic spinel structure of these compounds was destroyed after annealing at temperature above 700°C. The magnetization measurements indicate superparamagnetic behavior of the nanosized compounds produced. 相似文献
5.
Balwinder Kaur Monita Bhat F. Licci Ravi Kumar S.D. Kulkarni P.A. Joy K.K. Bamzai P.N. Kotru 《Journal of magnetism and magnetic materials》2006
Using vibrating sample magnetometery (VSM) 50 MeV Li3+ ion irradiation effects on magnetic properties of single crystals of SrGaxInyFe12−(x+y)O19 (where x=0, 5, 7, 9; y=0, 0.8, 1.3, 1.0), are reported. The substitution of Ga and In in strontium hexaferrite crystals decreases the value of magnetization sharply, which is attributed to shifting of collinear magnetic order to a non-collinear one. Reduction of magnetization is also explained to be as a result of the occupation of the crystallographic sites of Fe3+ by Ga3+ and In3+. The Li3+ ion irradiation decreases the value of magnetization, irrespective of whether the crystals are Ga–In substituted or unsubstituted crystals of SrFe12O19. The result is interpreted in terms of the occurrence of a paramagnetic doublet in crystals replacing magnetic sextuplet as a result of irradiation. Substitution of Ga–In in Strontium hexaferrite decreases the value of anisotropy constant. Irradiation with Li3+ ions increases the values of anisotropy field for both substituted as well as unsubstituted crystals. Substitution with Ga–In also decreases the Curie temperature (Tc) but the irradiation with Li3+ ions does not affect the curie temperature of either Ga–In substituted or pure SrFe12O19 crystals. 相似文献
6.
The magnetic properties of Co-ferrite-doped hydroxyapatite (HAP) nanoparticles of composition Ca10−3xFe2xCox(PO4)6(OH)2 (where x=0, 0.1, 0.2, 0.3, 0.4 and 0.5% mole) are studied. Transmission electron microscope micrograms show that the 90 nm size nanoparticles annealed at 1250 °C have a core/shell structure. Their electron diffraction patterns show that the shell is composed of the hydroxyapatite and the core is composed of the Co-ferrite, CoFe2O4. Electron spin resonance measurements indicate that the Co2+ ions are being substituted into the Ca(1) sites in HAP lattice. X-ray diffraction studies show the formation of impurity phases as higher amounts of the Fe3+/Co2+ ions which are substituted into the HAP host matrix. The presence of two sextets (one for the A-site Fe3+ and the other for the B-site Fe3+) in the Mössbauer spectrum for all the doped samples clearly indicates that the CoFe2O4.cores are in the ferromagnetic state. Evidence of the impurity phases is seen in the appearance of doublet patterns in the Mössbauer spectrums for the heavier-doped (x=0.4 and 0.5) specimens. The decrease in the saturation magnetizations and other magnetic properties of the nanoparticles at the higher doping levels is consistent with some of the Fe3+ and Co2+ which being used to form the CoO and Fe2O3 impurity phase seen in the XRD patterns. 相似文献
7.
A series of Mn–Zn Ferrite nanoparticles (<15 nm) with formula MnxZn1−xFe2O4 (where x=0.00, 0.35, 0.50, 0.65) were successfully prepared by citrate-gel method at low temperature (400 °C). X-ray diffraction analysis confirmed the formation of single cubic spinel phase in these nanoparticles. The FESEM and TEM micrographs revealed the nanoparticles to be nearly spherical in shape and of fairly uniform size. The fractions of Mn2+, Zn2+ and Fe3+ cations occupying tetrahedral sites along with Fe occupying octahedral sites within the unit cell of different ferrite samples are estimated by room temperature micro-Raman spectroscopy. Low temperature Mossbauer measurement on Mn0.5Zn0.5Fe2O4 has reconfirmed the mixed spinel phase of these nanoparticles. Room temperature magnetization studies (PPMS) of Mn substituted samples showed superparamagnetic behavior. Manganese substitution for Zn in the ferrite caused the magnetization to increase from 04 to18 emu/g and Lande's g factor (estimated from ferromagnetic resonance measurement) from 2.02 to 2.12 when x was increased up to 0.50. The FMR has shown that higher Mn cationic substitution leads to increase in dipolar interaction and decrease in super exchange interaction. Thermomagnetic (M–T) and magnetization (M–H) measurements have shown that the increase in Mn concentration (up to x=0.50) enhances the spin ordering temperature up to 150 K (blocking temperature). Magnetocrystalline anisotropy in the nanoparticles was established by Mossbauer, ferromagnetic resonance and thermomagnetic measurements. The optimized substitution of manganese for zinc improves the magnetic properties and makes these nanoparticles a potential candidate for their applications in microwave region and biomedical field. 相似文献
8.
Polycrystalline La2−xPrxCa2xBa2Cu4+2xOz (LPCaBCO) compounds with x=0.1-0.5 were synthesized by solid-state reaction method and studied by room temperature X-ray diffraction, dc resistivity, dc magnetization and iodometry. The superconducting transition temperatures in these tetragonal triple perovskite compounds increases from 32 to 62 K (Tconset values) with increasing dopant concentration. The mixing of rare earth La3+ and Pr3+/4+ ions at rare earth site (La3+) along with substitution of divalent Ca2+ results in the shrinkage of unit cell volume. The contraction of unit cell volume due to larger ion being substituted by smaller ions, gives rise to creation of pinning centres in the unit cell leading to increase in critical current density and flux pinning. 相似文献
9.
Kwang Joo Kim Hee Kyung Kim Young Ran Park Jae Yun Park 《Journal of magnetism and magnetic materials》2006
Effects of Mn substitution for Co and Fe on the structural and magnetic properties of inverse-spinel CoFe2O4 have been investigated. MnxCo1−xFe2O4 and MnyCoFe2−yO4 thin films were prepared by a sol–gel method. The observed increase of the lattice constant of MnxCo1−xFe2O4 indicates that Mn2+ ions substitute the octahedral Co2+ sites. Conversion electron Mössbauer spectroscopy data indicate that a fraction of octahedral Co2+ ions exchange sites with tetrahedral Fe3+ ions through Mn doping. Vibrating-sample magnetometry data exhibit a large increase of saturation magnetization for both MnxCo1−xFe2O4 and MnyCoFe2−yO4 films compared to that of the CoFe2O4 film. Such enhancement of magnetization can be explained in terms of a breaking of ferrimagnetic order induced by the Co2+ migration. 相似文献
10.
Zr1−xMxW2O8−y (M=Sc, In and Y) solid solutions substituted up to x=0.04 for Zr(IV) sites by M(III) ions were synthesized by a solid-state reaction. X-ray diffraction experiments from 90 to 560 K revealed that all solid solutions had a cubic crystal structure and showed negative thermal expansion coefficients. The lattice parameters of Zr1−xMxW2O8−y were smaller than that of ZrW2O8 probably due to oxygen defects, though the ionic radii of substituted M3+ ions were larger than that of Zr4+. Order-disorder phase transition temperatures of the substituted samples drastically decreased in the order of Y, In and Sc compared to the percolation theory, and decreased with increasing M content. 相似文献
11.
We have prepared polycrystalline Ca3−xEuxCo4O9+δ (x=0, 0.15, 0.3 and 0.45) samples using a sol-gel process followed by SPS sintering and investigated the Eu substitution effects on their high-temperature thermoelectric properties. With the Eu substitution, both the electrical resistivity and thermopower increase monotonously. This could be attributed to the decrease of hole concentrations by substitution of trivalent Eu3+ for divalent Ca2+. The Eu substituted samples (x=0.15, x=0.3) have lower thermal conductivity than Ca3Co4O9+δ due to their lower electronic and lattice thermal conductivity. The dimensionless figure of merit ZT reaches 0.3 at 1000 K for the sample of Ca2.7Eu0.3Co4O9+δ. 相似文献
12.
Mohammad Javad Nasr Isfahani Maxym Myndyk Jan Šubrt 《Journal of magnetism and magnetic materials》2010,322(13):1744-1747
The substituted nickel ferrite (NiFe2−2xSnxCuxO4, x=0, 0.1, 0.2, 0.3) was prepared by the conventional ceramic method. The effect of substitution of Fe3+ ions by Sn4+ and Cu2+ cations on the structural and magnetic properties of the ferrite was studied by means of 57Fe Mössbauer spectroscopy, alternating gradient force magnetometry (AGFM) and Faraday balance. Whereas undoped NiFe2O4 adopts a fully inverse spinel structure of the type (Fe)[NiFe]O4, Sn4+ and Cu2+ cations tend to occupy octahedral positions in the structure of the substituted ferrite. Based on the results of Mössbauer spectroscopic measurements, the crystal-chemical formula of the substituted ferrite may be written as (Fe)[NiFe1−2xSnxCux]O4, where parentheses and square brackets enclose cations in tetrahedral (A) and octahedral [B] coordination, respectively. The Néel temperature and the saturation magnetization values of the NiFe2−2xSnxCuxO4 samples were found to decrease with increasing degree of substitution (x). The variation of the saturation magnetization with x measured using the AGFM method and that calculated on the basis of the Mössbauer spectroscopic measurements are in qualitative agreement. 相似文献
13.
I. S. Édelman O. S. Ivanova K. P. Polyakova V. V. Polyakov O. A. Bayukov 《Physics of the Solid State》2008,50(12):2289-2294
This paper reports on the results of investigations into the structure and the magnetic and magnetooptical properties of thin films Mn x Fe3 ? x O4 prepared by solid-state reactions: isothermal annealing, self-propagating high-temperature synthesis, and a combination of these two regimes. The regimes favorable for the formation of films close in composition and structure to the stoichiometric compounds MnFe2O4 or Fe3O4 are established. The features observed in the spectral response of the magneto-optical Faraday effect and of the magnetic circular dichroism of the MnFe2O4 films are considered in terms of the electronic transitions in magnetic ions, primarily Fe3+, which occupy octahedral positions in the spinel structure. 相似文献
14.
Georgiana Dascalu Gloria Pompilian Bertrand Chazallon Valentin Nica Ovidiu Florin Caltun Silviu Gurlui Cristian Focsa 《Applied Physics A: Materials Science & Processing》2013,110(4):915-922
CoFe2O4 thin films with preferential texture structure, small grain size, and perpendicular magnetic anisotropy can be obtained by the pulsed laser deposition (PLD) technique. In this work, we studied the influence of the Fe3+ ions substitution by three elements from lanthanide group (Dy, La, and Gd) on the structural properties of the thin films. The samples were deposited by Nd:YAG laser (λ=532 nm, 10 ns) ablation of CoFe1.8RE0.2O4, (RE=Dy, La, Gd) targets at various substrate temperatures ranging from room temperature to 600 °C. The microstructure and chemical composition of the thin films were investigated by Raman spectroscopy, XRD, SEM-EDS, and ToF-SIMS. The XRD patterns and Raman spectra of the thin films indicated the formation of a single spinel structure. Thus, the desired substitution of the iron ions in the spinel lattice with the RE elements was achieved in the thin films, although in the bulk material, their presence determined the formation of a residual phase with a perovskite-type structure. 相似文献
15.
The effect of Fe substitution for Co on direct current (DC) electrical and thermal conductivity and thermopower of Ca3(Co1−xFex)4O9 (x = 0, 0.05, 0.08), prepared by a sol–gel process, was investigated in the temperature range from 380 down to 5K. The results indicate that the substitution of Fe for Co results in an increase in thermopower and DC electrical resistivity and substantial (14.9–20.4% at 300K) decrease in lattice thermal conductivity. Experiments also indicated that the temperature dependence of electrical resistivity ρ for heavily substituted compounds Ca3(Co1−xFex)4O9 (x = 0.08) obeyed the relation lnρ ∝ T−1/3 at low temperatures, T < ~55K, in agreement with Mott’s two-dimensional (2D) variable range hopping model. The enhancement of thermopower and electrical resistivity was mainly ascribed to a decrease in hole carrier concentration caused by Fe substitution, while the decrease of thermal conductivity can be explained as phonon scattering caused by the impurity. The thermoelectric performance of Ca3Co4O9 was not improved in the temperature range investigated by Fe substitution largely due to great increase in electrical resistivity after Fe substitution. 相似文献
16.
Prakash Chandra Sati Manisha AroraSunil Chauhan Manoj KumarSandeep Chhoker 《Journal of Physics and Chemistry of Solids》2014
Bi1−xDyxFeO3 (x=0.0, 0.03, 0.05, 0.07, 0.10 and 0.12) ceramics were synthesized by solid state reaction method. Effects of Dy substitution on structural distortion, magnetic and optical properties of BiFeO3 were examined by X-ray diffraction, Raman and UV–Visible spectroscopy. The samples were found to crystallize in rhombohedral structure of BiFeO3 with R3c space group. The reduction in lattice parameters and unit cell volume indicate the distortion in FeO6 octahedra of the rhombohedral structure without any signature of phase transformation up to x=0.12. The predictable weak ferromagnetic hysteresis loops can be observed in the Dy doped samples with maximum remnant magnetization of 0.2103 emu/g for x=0.12. The weak ferromagnetism is ascribed to the suppressed spiral spin structure and magnetically active characteristic of Dy3+ ions together with ferromagnetic coupling between Dy3+ and Fe3+ ions. With optical band gap in visible region, Dy doped BiFeO3 ceramics are potential material for optoelectronic device and solar cell applications. 相似文献
17.
The microwave characteristics of Co2+ and Ti4+ ions substituted, BaCo x Ti x Fe(12?2x)O19 (x = 0.1, 0.3, 0.5, 0.7, 0.9) ferrite have been studied as a function of thickness, frequency and substitution. The results depict reflection loss of ? 31.94 dB at 10.47 GHz in x = 0.9. The highest static electrical current is observed at lower substitution. The model accompanying microwave absorption is used to evaluate microwave absorption characteristics. The electromagnetic and static electrical characteristics are improved with the substitution of Co2+ and Ti4+ ions. The compositions for possible electromagnetic applications are also explored. 相似文献
18.
19.
Co1−xZnxFe2O4 nanoparticles were prepared by co-precipitation method with x varying from 0 to 1.0. The powder samples were characterized by X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and Fourier transform infrared spectroscopy (FTIR). The average crystallite sizes of the particles were determined from XRD. X-ray analysis showed that the samples were cubic spinel. The average crystallite size (DaveXR) of the particles precipitated was found to vary from 6.92 to 12.02 nm decreasing with the increase in zinc substitution. The lattice constant (ao) increased with the increase in zinc substitution. The specific saturation magnetization (MS) of the particles was measured at room temperature. The magnetic parameters such as MS, Hc, and Mr were found to decrease with the increase in zinc substitution. FTIR spectra of the Co1−xZnxFe2O4 with x varying from 0 to 1.0 in the range 400–4000 cm−1 were reported. The spinel structure and the crystalline water adsorption of Co1−xZnxFe2O4 nanoparticles were studied by using FTIR. 相似文献
20.
Measurements of the a.c.susceptibility (χ=χ′+iχ″) have been made on the Mg substituted high TC superconducting system, CuBa2(MgxCa1−x)3Cu4O12−y (Cu-1234) with x=0, 0.10 & 0.20, at different values of the a.c.field amplitude. Estimates of the intergranular critical current density(JC) made from the field dependent χ″-T curves show an improvement in the Mg-substituted Cu-1234 system. Results have been analysed in the light of the crystal structure and the superconducting anisotropy factor (γ=ξab/ξc) of the Cu-1234 system. Lower superconducting anisotropy emanating from Mg substitution has been found to be significant, resulting in better superconducting properties. 相似文献