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1.
CoFe2O4 particles were synthesized using metallic nitrates and polyvinylpyrolidone (PVP) using sol–gel method followed by calcination for 2 h at 960 °C. PVP performed as a surfactant and the effect of various concentrations of PVP on the resultant CoFe2O4 powder was studied. The resultant samples were characterized by XRD, TG/DSC, HR-SEM and VSM. X-ray diffraction results indicated the crystalline phase of CoFe2O4 particles and impurity phase of hematite was observed for higher PVP concentrations. SEM images demonstrated the influence of PVP concentration on the size of the particles. By VSM measurements, the variations in magnetic properties with respect to PVP concentration are studied. All the magnetic characteristics H c , M s and M r increased for 6 wt% and 15 wt% of PVP concentration. The CoFe2O4 particles synthesized with the optimum concentration of PVP may be very attractive for potential applications because of their outstanding magnetic properties (M s =81.1 Am2/kg, H c =831 Gauss).  相似文献   

2.
Ferromagnetic Mn-Al alloy powders were fabricated by mechanical milling and heat treatment with gas-atomized powders. Different processes, i.e., heat treatment before ball milling and ball milling before heat treatment, result in different microstructures and magnetic properties of the powders. It was found that Hc increased and Mr decreased with the size reduction regardless of the sequence of heat treatment and ball milling. However, tendency of the change in Hc and Mr depended on the sequence. Further annealing of the powders ball-milled after heat treatment resulted in slight decrease of Hc and large increase of Mr. The magnetic properties, Mr = 41.2 emu/g, Hc = 3.1 kOe, were obtained from the powders ball-milled for 5 h after heat treatment at 650 °C for 20 min, and subsequent annealing at 280 °C for 20 min.  相似文献   

3.
We report synthesis and magnetization of MSr2Y1.5Ce0.5Cu2O10 (M/Y-1222) compounds with M = Ru, Mn and Cr by HPHT. They are synthesized at high-pressure of 6 GPa in optimized temperatures of up to 1450 °C, for Ru, Mn and 1550 °C in the case of Cr based Y/1222, for a time duration of three hours for all the samples. All the samples crystallized with tetragonal structure in I4/mmm space group. Few minor impurities are also seen in the case of Mn,Cr/Y-1222 samples. DC magnetic susceptibility measurements exhibited ferromagnetic like transition for all the three compounds at low temperatures. At 5 K, the magnetization M(H) experiments showed clear ferromagnetic like hysteresis loops for Ru and Mn samples with sizeable returning moment (Mr) and coercive field (Hc). In the case of Cr/Y-1222 system though, ferromagnetism is visible below around 45 K in susceptibility measurements, the characteristic Mr and Hc are not seen. To the best of our knowledge the Mn,Cr/Y-1222 phases are synthesized for the first time and the quality of our earlier reported Ru/Y-1222 is improved.  相似文献   

4.
In the present study, mechanical alloying process was employed for preparation of the nanocrystalline (Fe85Ni15)97Al3 alloy through ball mill method. The structure, mechanical properties, and magnetic behavior of the alloy at various milling times of 0, 4, 16, 32 and 64 h were studied by X-ray analysis, vibrating sample magnetometer (VSM) and scanning electron microscopy (SEM) measurements. The bcc Fe(Ni) phase was successfully formed within 32 h ball-milling. It was found that an increment in the milling time leads to higher lattice parameter while it decreases the grain size from 172 to 16 nm. Also, the VSM test results indicated that by increasing the milling time to 32 h, the saturation magnetization (Ms) and coercivity (Hc) increased.  相似文献   

5.
Magnetic studies of La-modified BiFeO3 ceramic with x = 0.0, 0.20 and 0.25 synthesized by solution combustion method are reported. X-ray diffraction, Differential scanning calorimetry and Vibrating sample magnetometer are used to characterize the powder samples. La substitution for Bi in BiFeO3 ceramic increased the Room-temperature saturation magnetization (Ms) and remanent magnetization (Mr). Mössbauer spectroscopy confirmed the presence of single-phase material for the doped compositions. A significant enhancement of antiferromagnetic Neel temperature TN and saturation magnetization Ms for x = 0.25 sample is observed as compared to BiFeO3.  相似文献   

6.
Multiferroic BiFe0.95Co0.05O3 thin films were fabricated on Pt/Ti/SiO2/Si substrates at various temperatures by pulsed laser deposition. It was found the deposition temperature had great effects on phase purity, orientation, microstructure and multiferroic properties of these films. The optimized deposition temperature was close to 600?°C. Polarization–electric field (P–E) and magnetization–magnetic field (M–H) hysteresis loops at room temperature were observed simultaneously in the films fabricated at 600?°C. The remnant polarization, coercive electric field (P r , E c ) and the remnant magnetization, coercive magnetic field (M r , H c ) of the films deposited at 600?°C were (0.95?μC/cm2, 31?kV/cm) and (0.59?emu/cm3, 130 Oe), respectively. These results might have implications for further investigations on high quality BiFe0.95Co0.05O3 multiferroic films.  相似文献   

7.
CoFe2O4 thin films of different thicknesses were grown on SrTiO3 substrates. The X-ray diffraction analysis and atomic force microscopy indicated both epitaxy and a granular microstructure. We studied the magnetic properties of these films as a function of oxygen post-annealing and film thickness. All as-deposited films exhibited similar magnetic properties with saturated magnetization (Ms) of approximately 50% of the bulk Ms, (80 Am2 kg− 1). After the post-annealing the Ms changes as a consequence of crystallographic restructuring of the film. Cation ordering in 100 nm thick films reduces Ms, whereas re-oxidation increases Ms for thinner films. 13 nm films, annealed for 1 h, reach the bulk Ms. For even thinner films the quantum-size effect reduces Ms. For a synthesis of ≥ 30 nm films an annealing cycle after deposition of every 15 nm layer is recommended.  相似文献   

8.
We present the electromagnetic properties of Mn doped Ge quantum dots (QDs)/Si electromagnetic diode. The Ge:Mn QDs were grown with a GeH4/Ar mixed gas under a constant flow at 500 °C by means of a plasma enhanced chemical vapor deposition (PECVD) process. They were then doped with different concentrations of Mn using a magnetron sputtering technique and annealed at 600 °C. The Ge:Mn QD samples show wildly open smooth hysteresis loops. The remnant magnetization Mr and saturation magnetic intensity Ms are functions of the doping concentration of Mn. The electromagnetic diodes fabricated in this way exhibit perfect electromagnetic, current–voltage (IV) and capacitance–voltage (CV) properties. The largest voltage and magnetic resistance differences with and without magnetic field are up to 4 V and 169 kΩ, respectively. These electromagnetic properties of the Ge1?xMnx QDs/Si diodes can be used to make various electromagnetic devices, including switches and storages devices.  相似文献   

9.
Ni0.5Zn0.5Fe2.0O4.0 thin films (NZFs) were deposited on Si (100) substrate by a sol–gel method, and the effects of annealing parameters on the structure and magnetic properties of the proposed films were investigated. Moderate heating rate was beneficial to the nucleation of NZFs. When the heating rate was 2 °C/min the saturation magnetization (M s) achieved its maximum and the coercivity (H c) reached its minimum. Both the crystallization and M s of NZFs enhanced with increasing annealing time; however, H c changed contrarily. High quenching temperature produced a large stress and consequently deteriorated magnetic properties. The optimal annealing parameters of NZFs were annealed at 700 °C, heating rate 2 °C/min, annealing time 1 h, and gradually cooled to room temperature. Finally, NZFs showed a high magnetization of 320 emu/cm3 and low coercivity of 86 Oe.  相似文献   

10.
X. Wang  W.T. Zheng  Yan Chen 《Thin solid films》2009,517(15):4419-4424
Influence of nitrogen fractions [Nf = N2/(N2 + Ar)] and sputtering powers (Ps) on the structural and magnetic properties of Co-N thin films synthesized by direct current magnetron sputtering have been studied. With increasing Nf from 0 to 20%, a series of phases from β-Co, β-Co (N), Co4N to Co3N were obtained. However, when Nf was fixed at 10%, only Co4N phase with different Co contents in the films was prepared, whose values of saturation magnetism (Ms) increased from 12.9 ± 8.2 Am2/kg to 103.9 ± 6.1 Am2/kg with the increase of Ps. Interstitial nitrogen caused the decrease of coercivity from 24.12 kAm− 1 (for β-Co film) to 2.71 kAm− 1. However, the addition of interstitial nitrogen was not observed to increase the Ms of β-Co.  相似文献   

11.
Some magnetic properties of the spinel structure compound, Li0.5+0.5x Ti x Fe2.5-1.5x O4, wherex=0–0.5, have been studied by different methods. The initial permeability, i, was measured as a function of temperature at a constant frequency of 10 kHz. A maximum value was observed for each composition indicating the Curie temperature,T c , which decreases with increasing titanium concentration. The magnetization,M, and theB-H loop were measured atRT in the range of magnetizing field from 0–1200 Am–1 and at constant fieldH=205 Am–1, respectively. The relative permeability, r, depends on the magnetizing field and composition. It was found from theB-H loop that the remanence induction,B r, and the apparent loss energy,P s, depend on the composition but the coercive force,H c, is independent of composition.  相似文献   

12.
In the present study, we have investigated the influence of different types of doping elements on magnetic properties of M-type BaFe12O19 samples. It was observed that Nb2O5 addition increases the coercive field, the remanence magnetization (M r), and saturation magnetization (M s) values by about 27 %, 47 %, and 53 %, respectively. In the same manner, MnO2 also improves the magnetic parameters significantly. The M r and M s values show increments up to 40 % in magnitude. On the other hand, the best magnetic properties were achieved by the addition of CuO to the B2O3 doped BaFe12O19. These materials have M r and M s values up to ~34 emu/g and ~62 emu/g, respectively.  相似文献   

13.
We have studied magnetic nanoparticles of cobalt ferrite obtained by the extraction-pyrolysis method in a mesoporous silicon dioxide (MSM-41) molecular sieve matrix. The X-ray diffraction data show evidence for the formation of CoFe2O4 particles with a coherent scattering domain size of ∼40 nm. Measurements of the magnetization curves showed that powders consisting of these nanoparticles are magnetically hard materials with a coercive field of H c(4.2 K) = 9.0 kOe and H c(300 K) = 1.8 kOe and a reduced remanent magnetization of M r/M s(4.2 K) = 0.83 and M r/M s(300 K) = 0.49. The shape of the low-temperature (4.2 K) magnetization curves is adequately described in terms of the Stoner-Wohlfarth model for randomly oriented single-domain particles with a cubic magnetic anisotropy.  相似文献   

14.
Cu–Al substituted Co ferrite nanopowders, Co1?x Cu x Fe2?x Al x O4 (0.0 ≤ x ≤ 0.8) were synthesized by the co-precipitation method. The effect of Cu–Al substitution on the structural and magnetic properties have been investigated. X-ray diffraction (XRD) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM) are used for studying the effect of variation in the Cu–Al substitution and its impact on particle size, magnetic properties such as M s and H c . Cu–Al substitution occurs and produce a secondary phase, α-Fe 2 O 3. The crystallite size of the powder calcined at 800 °C was in the range of 19–26 nm. The lattice parameter decreases with increasing Cu–Al content. The nanostructural features were examined by FESEM images. Infrared absorption (IR) spectra shows two vibrational bands; at around 600 (v 1) and 400 cm ?1 (v 2). They are attributed to the tetrahedral and octahedral group complexes of the spinel lattice, respectively. It was found that the physical and magnetic properties have changed with Cu–Al contents. The saturation magnetization decreases with the increase in Cu–Al substitution. The reduction of coercive force, saturation magnetization and magnetic moments are may be due to dilution of the magnetic interaction.  相似文献   

15.
Co80Ni20 powder mixture was mechanically alloyed by high-energy planetary ball milling, starting from elemental Co and Ni metal powders. The morphological, microstructural, thermal and magnetic properties of the milled powders were characterised respectively by scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and vibratory sample magnetometry. In addition to a highly disordered phase, two face-centred cubic (FCC) and hexagonal close-packed (HCP), solid solutions, FCC Co(Ni), FCC Ni(Co) and HCP Co(Ni), are observed after 3 h of milling. Their grain sizes decrease with increase in milling time attaining, at 48 h of milling, 12 nm, 25 nm and 10 nm, respectively. Beyond a certain milling time, no further refinement of the microstructure occurs and the morphological equilibrium is usually given by a bimodal particle size distribution. Magnetic measurements of the milled Co80Ni20 alloy powder exhibit a soft ferromagnetic character where the magnetic parameters are sensitive to the milling time mainly due to the particle size refinement as well as the formation of Co(Ni) and Ni(Co) solid solutions. Both the saturation magnetisation ( M s) and coercivity ( H c) were found to decrease with milling time, attaining the values of M s = 126 emu/g and H c = 60 Oe after 48 h of milling.  相似文献   

16.
Nanostructured M-type hexaferrite Ba1?x Ca x Fe11.5Cr0.5O19 (x=0.0–0.5) powders have been synthesized by means of the sol-gel autocombustion method. The materials are characterized by differential scanning calorimetry, thermogravimetry, Fourier transform infra-red spectroscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and vibrating sample magnetometry. X-ray diffraction analysis confirms the formation of M-type hexagonal phase and few traces of α-Fe2O3 are also observed. The c/a ratio falls in the expected range from a value of 3.97 to 3.94 of M-type hexaferrites. The average crystallite size is found to be in the range 15 to 36 nm, which is good enough to obtain the suitable signal-to-noise ratio in the high-density recording media. DC electrical resistivity at room temperature enhances up to 11.2×109 Ω?cm (x=0.4) and then drops upon increasing the Ca2+ contents further. The magnetic properties such as saturation magnetization (M s ), remanence (M r ), squareness ratio (M r /M s ) and coercivity (H c ) are calculated from the MH-loops. The maximum magnetization and remanence reduces from a value of 52 to 33 and 33 to 16 emu/g, respectively, which attributes to the decrease of magnetic moment, and hence reduction in the superexchange interaction. The coercivity enhances from 4378 to 4706 Oe, which attributes to the increase in magnetocrystalline anisotropy due to the reduction of particle size. Owing to these properties, the synthesized nanomaterials can be considered useful for high-density recording media and permanent magnets.  相似文献   

17.
Zn0.92Co0.08O thin films were fabricated on p-type Si (100) and quartz substrates by pulsed laser deposition using a ZnCoO ceramic target. The structural and magnetic properties of the films were characterized by field emission scan electronic microscopy, x-ray diffraction, x-ray photoemission spectroscopy, UV-visible transmission spectra, extended x-ray absorption fine structure spectroscopy and physical property measurement system. Substitutional doping of Co2+ in ZnO lattice is demonstrated in the films. The as-deposited Zn0.92Co0.08O thin film displayed intrinsic room temperature ferromagnetism with saturation magnetization (Ms) of ~ 0.20μB/Co. The corresponding Ms increased to ~ 0.23μB/Co when annealed in vacuum and further to ~ 0.42μB/Co after annealed in hydrogen. In turn, the Ms dropped to the value of ~ 0.13μB/Co after annealed in oxygen. Our studies indicate that oxygen vacancy density plays a key role in mediating the ferromagnetism of the diluted magnetic semiconductor films.  相似文献   

18.
In the present study, we investigate influence of HCl-etching on magnetic parameters of B2O3-doped M-type barium ferrites. Our studies have shown that magnetization parameters; the remanence magnetization M r and the specific magnetization M s at 1.5?T, increase significantly with HCl-etching. The best magnetic parameters were observed in the sample of 0.1?wt% B2O3-doped and HCl-washed one after calcination at 1000?°C (M r =34.9?emu/g, M s =0.63.3?emu/g). Increments up to 50% in magnitudes could be achieved with HCl washing. Exchange interactions between particles were also examined by Wohlfarth model. It was observed that magnetizing-like interactions between particles become stronger but ,on the other hand, demagnetizing-like interactions becomes weaker with HCl-etching.  相似文献   

19.
We report on the preparation and characterization of high purity manganese (3–9 wt.%) doped indium tin oxide (ITO, In:Sn = 90:10) films deposited by sol–gel mediated dip coating. X-ray diffraction and selected area electron diffraction showed high phase purity cubic In2O3 and indicated a contraction of the lattice with Mn doping. High-resolution transmission electron microscopy depicted a uniform distribution of ∼20 nm sized independent particles and particle induced x-ray emission studies confirmed the actual Mn ion concentration. UV-Vis diffuse reflectance measurements showed band gap energy of 3.75 eV and a high degree of optical transparency (90%) in the 100–500 nm thick ITO films. X-ray photoelectron spectroscopy core level binding energies for In 3d5/2 (443.6 eV), Sn 3d5/2 (485.6 eV) and Mn 2p3/2 (640.2 eV) indicated the In3+, Sn4+ and Mn2+ oxidation states. Magnetic hysteresis loops recorded at 300 K yield a coercivity Hc ∼ 80 Oe and saturation magnetization Ms ∼ 0.39 μB/Mn2+ ion. High-temperature magnetometry showed a Curie temperature T c > 600 K for the 3.2% Mn doped ITO film.  相似文献   

20.
《Advanced Powder Technology》2021,32(12):4846-4856
Fe-Si/MnO-SiO2 soft magnetic composites (SMCs) are prepared by sintering ball milled Fe-Si/MnO2 core–shell structured composites. The correlation between the coating uniformity and electromagnetic properties have been investigated via adjusting ball milling parameters in detail. The results indicate that uniform MnO2 coating can be transformed into MnO-SiO2 composite coatings with high insulation due to the high temperature reaction between MnO2 and Si. Agate ball is more effective than stainless steel ball to improve the uniformity of MnO2 coating as well as the electromagnetic properties such as significantly higher resistivity, lower core loss and better frequency stability of permeability. Moreover, increasing the ball milling time from 4 h to 24 h can obviously improve the coating uniformity and thus result in the remarkable increase of the resistivity from 2.4 mΩ·cm to 356.9 mΩ·cm. And the core loss and dynamic loss decrease rapidly while the Ms shows a slight decline. When the ball milling time reaches 24 h, the Fe-Si SMCs exhibits superior magnetic properties such as high Ms (181.0 emu/g), very low core loss (361.5 kW/m3 at 100 kHz) and good frequency stability of permeability (65) from 50 Hz to 1000 kHz.  相似文献   

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