Study of CoFe2O4 Particles Synthesized with Various Concentrations of PVP Polymer

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).     

Effect of mechanical milling and heat treatment on the structure and magnetic properties of gas atomized Mn-Al alloy powders

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 H_c increased and M_r decreased with the size reduction regardless of the sequence of heat treatment and ball milling. However, tendency of the change in H_c and M_r depended on the sequence. Further annealing of the powders ball-milled after heat treatment resulted in slight decrease of H_c and large increase of M_r. The magnetic properties, M_r = 41.2 emu/g, H_c = 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.     

High-pressure high-temperature (HPHT) synthesis and magnetism of MSr2Y1.5Ce0.5Cu2O10 compounds with M = Ru, Mn, and Cr

We report synthesis and magnetization of MSr₂Y_1.5Ce_0.5Cu₂O₁₀ (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 (M_r) and coercive field (H_c). In the case of Cr/Y-1222 system though, ferromagnetism is visible below around 45 K in susceptibility measurements, the characteristic M_r and H_c 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.     

Effect of aluminum on microstructural and magnetic properties of nanostructured (Fe85Ni15)97Al3 alloy produced via mechanical alloying

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 (M_s) and coercivity (H_c) increased.     

Room-temperature magnetic studies of La-modified BiFeO3 ceramic

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 (M_s) and remanent magnetization (M_r). Mössbauer spectroscopy confirmed the presence of single-phase material for the doped compositions. A significant enhancement of antiferromagnetic Neel temperature T_N and saturation magnetization M_s for x = 0.25 sample is observed as compared to BiFeO₃.     

Effects of deposition temperature on phase purity, orientation, microstructure and property of cobalt substituted bismuth ferrite thin films

Multiferroic BiFe_0.95Co_0.05O₃ 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 BiFe_0.95Co_0.05O₃ multiferroic films.     

Chemistry of post-annealing of epitaxial CoFe2O4 thin films

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 (M_s) of approximately 50% of the bulk M_s, (80 Am² kg^− 1). After the post-annealing the M_s changes as a consequence of crystallographic restructuring of the film. Cation ordering in 100 nm thick films reduces M_s, whereas re-oxidation increases M_s for thinner films. 13 nm films, annealed for 1 h, reach the bulk M_s. For even thinner films the quantum-size effect reduces M_s. For a synthesis of ≥ 30 nm films an annealing cycle after deposition of every 15 nm layer is recommended.     

The electromagnetic properties of the Mn doped Ge/Si quantum dots diodes

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 M_r and saturation magnetic intensity M_s are functions of the doping concentration of Mn. The electromagnetic diodes fabricated in this way exhibit perfect electromagnetic, current–voltage (I–V) and capacitance–voltage (C–V) 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 Ge_1?xMn_x QDs/Si diodes can be used to make various electromagnetic devices, including switches and storages devices.     

Effect of annealing parameters on the magnetic properties of NiZn ferrite thin films

Ni_0.5Zn_0.5Fe_2.0O_4.0 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.     

Structural and magnetic properties of Co-N thin films synthesized by direct current magnetron sputtering

Influence of nitrogen fractions [N_f = N₂/(N₂ + Ar)] and sputtering powers (P_s) on the structural and magnetic properties of Co-N thin films synthesized by direct current magnetron sputtering have been studied. With increasing N_f from 0 to 20%, a series of phases from β-Co, β-Co (N), Co₄N to Co₃N were obtained. However, when N_f was fixed at 10%, only Co₄N phase with different Co contents in the films was prepared, whose values of saturation magnetism (M_s) increased from 12.9 ± 8.2 Am²/kg to 103.9 ± 6.1 Am²/kg with the increase of P_s. 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 M_s of β-Co.     

The effect of Ti4+ ions on some magnetic properties of lithium ferrite

Some magnetic properties of the spinel structure compound, Li_0.5+0.5x Ti _x Fe_2.5-1.5x 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.     

The Influences of Nb2O5, MnO2, CuO and B2O3 Addition on the Magnetic Properties of BaFe12O19 Magnets

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.     

Cobalt ferrite nanoparticles in a mesoporous silicon dioxide matrix

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.     

Cu<Superscript>2+</Superscript> and Al<Superscript>3+</Superscript> co-substituted cobalt ferrite: structural analysis,morphology and magnetic properties

Cu–Al substituted Co ferrite nanopowders, Co_1?x Cu _x Fe_2?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.     

Structural,Thermal and Magnetic Properties of Nanocrystalline Co<Subscript>80</Subscript>Ni<Subscript>20</Subscript> Alloy Prepared by Mechanical Alloying

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.     

Structural, Electrical, and Microstructure Properties of Nanostructured Calcium Doped Ba-Hexaferrites Synthesized by Sol-Gel Method

Nanostructured M-type hexaferrite Ba_1?x Ca _x Fe_11.5Cr_0.5O₁₉ (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 M–H-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.     

Towards Further Improvements of the Magnetization Parameters of B2O3-Doped BaFe12O19 Particles: Etching with Hydrochloric Acid

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.     

Intrinsic room temperature ferromagnetism in Zn0.92Co0.08O thin films prepared by pulsed laser deposition

Zn_0.92Co_0.08O 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 Zn_0.92Co_0.08O thin film displayed intrinsic room temperature ferromagnetism with saturation magnetization (M_s) of ~ 0.20μ_B/Co. The corresponding M_s increased to ~ 0.23μ_B/Co when annealed in vacuum and further to ~ 0.42μ_B/Co after annealed in hydrogen. In turn, the M_s dropped to the value of ~ 0.13μ_B/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.     

Effect of Mn doping on the structural,morphological, optical and magnetic properties of indium tin oxide films

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 3d_5/2 (443.6 eV), Sn 3d_5/2 (485.6 eV) and Mn 2p_3/2 (640.2 eV) indicated the In³⁺, Sn⁴⁺ and Mn²⁺ oxidation states. Magnetic hysteresis loops recorded at 300 K yield a coercivity H_c ∼ 80 Oe and saturation magnetization M_s ∼ 0.39 μ_B/Mn²⁺ ion. High-temperature magnetometry showed a Curie temperature T _c > 600 K for the 3.2% Mn doped ITO film.     

Highly enhancing electromagnetic properties in Fe-Si/MnO-SiO2 soft magnetic composites by improving coating uniformity

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 M_s shows a slight decline. When the ball milling time reaches 24 h, the Fe-Si SMCs exhibits superior magnetic properties such as high M_s (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.