Fine Fe16N2 powder prepared by low-temperature nitridation

α-Fe was prepared by reduction of a fine γ-Fe₂O₃ powder under hydrogen at 500 °C for 8 h. The α-Fe fine powder, about 100 nm in crystallite size, was then nitrided under an ammonia flow at 130 °C for 100 h. X-ray single-phase Fe₁₆N₂ was obtained with a magnetization value of 225 emu/g at room temperature under a magnetic field of 15 kOe. The Mössbauer spectrum at room temperature could be resolved into three sets of hyperfine fields with an average magnetic moment of 2.52 μ_B. An additional paramagnetic component was present in the spectrum with an area ratio of 19%.     

Hydrothermal Synthesis of SrFe12O19 and Its Characterization

We have synthesized strontium hexaferrite particles in an alkaline medium using a hydrothermal process at 180?°C. Crystalline phase of samples were determined by XRD and spectroscopic, morphological, and magnetic investigation of the sample were FT-IR, SEM, and TG analysis, respectively. XRD analysis revealed few impurity phases in the as-made powder; upon calcinations, the material is converted to desired hexaferrite phase. As synthesized powder exhibits agglomerates with rather smooth facets, in the form of thick platelets. Upon calcination, all these structures were observed to transfer to rod-like structures. The As calcined sample has high specific saturation magnetization (M _s ) values of 65?emu/g that is close to its theoretical value of 74.3?emu/g but the hydrothermally synthesized sample does not. This is in agreement with the observations from XRD analysis where few impurity phases observed in the as-made powder cause a weak magnetic response. Upon calcination, the material is converted to a desired hexaferrite phase with better magnetic properties.     

The Effect of EDTA on the Synthesis of Ni Ferrite Nanoparticles

Nanocrystalline nickel ferrite (NiFe₂O₄) was synthesized by chemical sol-gel method using Ethylenediamine tetra acetic acid (EDTA) as a complexing agent. The results show that by using EDTA, it is possible to prepare pure phase of nickel ferrite nanoparticles at the relatively low temperatures. The annealing temperature is found to have strong influence on size, structural, and magnetic properties of the synthesized samples. It was found that the values of saturation magnetization, M _s increases by the increasing of the annealing temperature. The largest value of M _s, was found to be 47?emu/g for the sample annealed at 1000?°C, which is close to the reported value for the multi-domain bulk samples of nickel ferrite (50?emu/g). Furthermore, as the particle size increases the coercivity starts to increase and reaches a maximum value; then it decreases. This effect can be attributed to the transition of the particle size from single-domain to the multi-domain magnetic structure.     

Magnetic and magneto-optical properties of amorphous boron-cobalt and silicon-cobalt alloys

Amorphous alloys of the type B_1?xCo_x and Si_1?xCo_x were prepared by vapour deposition.Their magnetic properties were determined in the range 4.2 - 300 K. The polar Kerr rotation was measured at two wavelengths (λ = 633 nm and 830 nm) at room temperature. The magnetic properties of these alloys were compared with amorphous alloys in which Co is combined with Sn, P, Mg, Y, La or Zr. The magnetic properties were analysed in terms of a model in which proper account is taken of possible differences in chemical short-range ordering of the atoms.     

Preparation and characterization of nanosized magnesium ferrite powders by a starch-gel process and corresponding ceramics

The synthesis and characterization of nanosized MgFe₂O₄ by a starch-gel method is described herein. A phase-pure nanosized MgFe₂O₄ powder (1a) was obtained after calcining a (MgFe)-starch gel at 550 °C. The powder has a specific surface area of 60.6 m²/g and a crystallite size of 9 nm. TEM investigations reveal particles in the range of 7–15 nm. The activation energy of the crystallite growth process was calculated as 89 ± 14 kJ/mol. The shrinkage and sintering behaviour of resulting compacts were studied. UV–Vis investigations of the nanosized powder 1a reveal an optical band gap of 2.38 eV, whereas calcination at 1100 °C (powder 1g) leads to a crystallite size of 129 nm and a band gap of 2.16 eV. Magnetization loops at 300 K and the temperature dependence of both the field-cooled and the zero-field-cooled magnetization indicate a superparamagnetic behaviour. The blocking temperature for powder 1a was determined as 140 K at a field of H = 500 Oe. We found different saturation magnetizations (M _s) depending on the calcination temperature. Calcination at 550 °C (1a) results in M _s = 20.0 emu/g which increases with calcination temperature to a maximum of 37.7 emu/g for powder 1e calcined at 900 °C. Ceramic bodies sintered between 1450 and 1600 °C exhibit M _s values of 25–28 emu/g. Magnetic investigations at 10 K on powders 1a–1g show hysteresis loops with coercivities up to 950 Oe, remanences to 10 emu/g and M _s values to 50.4 emu/g. Additionally, the nanoscaled powders show a shift of the hysteresis loops.     

Magnetic Properties of Nanocrystalline CoFe2O4/ZnFe2O4 Bilayers

Nanocrystalline spinel CoFe₂O₄/ZnFe₂O₄ bilayers were deposited by the pulsed laser deposition technique on amorphous fused quartz substrate at different substrate temperatures ranging from room temperature to 750?°C. The magnetic properties of the bilayers and of the single layer films deposited in identical conditions were studied at 300?K and at 10?K. Magnetic properties of the bilayers, in general, were found to be in between the individual values of the single layers. Magnetic measurements at 10?K clearly showed a two stepped magnetic hysteresis loop corresponding to the switching of the magnetic moments of the soft ZnFe₂O₄ and the hard CoFe₂O₄ layers. A study was also carried out by changing the thickness of ZnFe₂O₄ layer in the bilayer. This study showed that the magnetic properties of the bilayers even at room temperature can be controlled to some extent by changing the thickness of the soft ZnFe₂O₄ layer while maintaining a low substrate temperature of 350?°C.     

Synthesis and Study of Structural,Morphological and Magnetic Properties of ZnFe2O4 Nanoparticles

Superparamagnetic zinc ferrite (ZnFe₂O₄) nanoparticles were prepared by a surfactant assisted hydrothermal method and subjected to the heat treatment. The structure, vibrational, morphology, and magnetic properties of synthesized product were characterized by XRD, FT-IR, HR-SEM, and VSM measurements. XRD result confirms the formation of regular spinel structured ZnFe₂O₄ with space group of Fd3m and an average crystalline size was calculated as 21 nm and 28 nm for the samples annealed in air atmosphere at 300 °C and 600 °C. The HR-SEM image shows that the particles are in spherical shape with small aggregation. A room temperature superparamagnetic behavior was observed for both samples. The saturation magnetization (M _s) of 12.0 emu/g and 9.10 emu/g were observed for the samples annealed in air atmosphere at 300 °C and 600 °C, respectively.     

Structural and Magnetic Properties of Cobalt and Manganese Doped Ni-Ferrite Nanoparticles

This study reports that NiCoMn ferrite [Ni_(1?x)Co _x Mn _y Fe_(2?y)O₄ with (x=y=0.01,0.02)] powders are prepared by using the sol-gel combustion method. The effect of various calcination temperatures on their structural and magnetic properties is also investigated. Structural properties of the powders are carried out by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). According to XRD analysis, all samples of two compositions have cubic spinel structure, with an enlargement in crystalline size is observed with increasing of calcination temperature. The crystallite size of the nanopowders is estimated from (311) peaks using Scherrer’s formula. Spherical particles of nanocrystalline ferrite powders are shown in TEM photographs. The room temperature magnetic properties of particles are studied by using a vibrating sample magnetometer (VSM). The magnetization measurements also indicated that the saturation magnetization (M _s) increases as the calcinations temperature increases for both A and B samples in the range of 31.69 to 47.77 and 21.81 to 48.89 emu/gr, respectively. The value of coercivity fields (H _c) decrease with increasing the calcinations temperature. Furthermore, the properties of two samples synthesis at the optimum calcinations temperature (800 ^°C) compared together.     

Annealing Effect on Structural and Magnetic Properties of Cu2MnAl Heusler Alloy Films

Cu₂MnAl Heusler alloy films were grown on MgO (001) substrates by using the ion beam sputtering technique. The films were post-annealed at varying temperatures in order to investigate the influence of annealing on crystal structure and magnetic properties. The structural properties of Cu₂MnAl films have been investigated by using x-ray diffraction (XRD) and magnetic properties have been investigated by both vibrating sample magnetometer (VSM) and ferromagnetic resonance (FMR) techniques. The experimental data indicates that the crystal structure of the films strongly depends on the annealing temperature. When the films were annealed at 200?°C, the saturation magnetization (M _s =250?emu/cm³) achieved its maximum and the coercive field (H _c ??7?Oe) reached its minimum with B2 ordered structure. In addition, FMR results have revealed that the Cu₂MnAl film annealed 200?°C has the highest effective magnetization. The combination of structural and magnetic characterization indicates that the optimum growth temperature is 200?°C for the Cu₂MnAl Heusler alloy films on MgO substrates.     

Synthesis of single-phase Sr3Co2Fe24O41 Z-type ferrite by polymerizable complex method

Synthesis of single-phase Sr₃Co₂Fe₂₄O₄₁ Z-type (Sr₃Co₂Z) ferrite was realized by adopting the polymerizable complex method. Crystal structure of samples has been investigated by powder X-ray diffraction (XRD). Single-phase Sr₃Co₂Z ferrite was obtained by heating at 1473 K for 5 h in air. Magnetic properties were discussed by measurements of M-H curves with vibrating sample magnetometer (VSM). Sr₃Co₂Z ferrite prepared by polymerizable complex method showed typical M-H curve of soft ferrite, with a saturation magnetization of 21.5μ_B/formula unit (50.5 emu/g) and a coercive force of 0.014 T at room temperature.     

Spin-Reorientation and M?ssbauer Study of Orthoferrite TbFe0.75Mn0.25O3

The crystallographic and magnetic properties of TbFe_0.75Mn_0.25O₃ powder were characterized by x-ray diffraction (XRD), Mössbauer spectroscopy, and vibrating-sample magnetometry (VSM). The crystal structure was found to be orthorhombic (space group Pbnm) with lattice constants a ₀=5.317 Å, b ₀=5.604 Å, and c ₀=7.598 Å, respectively. Mössbauer spectra of TbFe_0.75Mn_0.25O₃ have been taken at various temperatures ranging from 4.2 to 550 K. For Mössbauer spectra, we have fitted the spectra to a model based on a random distribution of Fe and Mn ions on the octahedral sites. The magnetic hyperfine fields of the four pattern (B ₀,B ₁,B ₂,B ₃) at 4.2 K are found to be H _hf=553, 544, 535, and 527 kOe, respectively. Isomer shift at room temperature is 0.25?C0.26 mm/s, which means that the valence state of Fe ions is ferric (Fe³⁺). A sudden change in both the magnitude of magnetic hyperfine field and its slope between 150 and 220 K suggests that magnetic phase transition related to the spin ordering takes place abruptly. The Néel temperature was determined to be T _N=550±5 K. The inflection points arising from a spin reorientation in the temperature dependence of the magnetic moment is observed. Its spin-reorientation transition is 70 K lower than that of 250 K for pure TbFeO₃.     

Synthesis and characterisation of pure single-phase CoFe2O4 nanopowder via a simple aqueous solution-based EDTA-precursor route

Single-phase cobalt ferrite (CoFe₂O₄) nanopowder, with average particle size ～20?nm, has been synthesised using an ethylene diamine tetra acetic acid precursor-based method. CoFe₂O₄ nanopowder was obtained by calcining precursor at 550°C for 4?h in air. The change of microstructure of the synthesised CoFe₂O₄ with increasing sintering temperature was studied using scanning electron microscopy. DC electrical resistivities of unsintered and sintered samples were measured using a two-probe method. Room temperature magnetic hysteresis measurement revealed that the synthesised CoFe₂O₄ nanopowder exhibited ferromagnetic behaviour at room temperature with saturation magnetisation of 67.55?emu/g and coercivity of 1645.24?Oe.     

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.     

Hydrothermal synthesis and characterization of monodisperse α-Fe2O3 nanoparticles

Monodisperse α-Fe₂O₃ nanoparticles have been successfully prepared by hydrothermal synthetic route using FeCl₃, CH₃COONa as reagents and reacted at 200 °C for 12 h. The morphology and structure of products were characterized by powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that the α-Fe₂O₃ nanoparticles were single-crystalline hexagonal structure and average diameters were about 80 nm. Magnetic properties have been detected by a vibrating sample magnetometer at room temperature. The nanoparticles exhibited a ferromagnetic behavior with the coercive force (Hc), saturation magnetization (Ms) and remanent magnetization (Mr) was 185.28 Oe and 0.494 emu/g, 0.077 emu/g.     

Magnetic State and Magnetocaloric Effect of SmMnO3

We present a study of magnetization and magnetocaloric effect for the SmMnO₃ compound. This compound was synthesized by combustion reaction and its magnetic and structural properties studied by X-ray powder diffraction (XRD) and magnetization (M) measurements as a function of temperature and under magnetic fields. The XRD pattern at room temperature confirmed the presence of a single phase with orthorhombic structure. From magnetization versus temperature, we observe two magnetic orderings, the first one at 6 K due to Sm³⁺, and the other one at T _N =57(2) K is the anti-ferromagnetic long-range ordering. The magnetic entropy change, ΔS _M , was obtained from magnetization isotherms close to T _N where it reaches a maximum value of about 8.0 J/kg K for an applied field of 7 T.     

Hard magnetic nanocrystalline alloys of Fe-O system

The structure and magnetic properties of nanocrystalline Fe-O alloys produced by high-energy ball milling and subsequent low-temperature annealing were investigated. The Fe₂O₃, FeO and Fe powders as well as their mixtures were used as starting materials. The structure was studied by X-ray diffraction analysis, Mössbauer spectroscopy and scanning electron microscopy. The magnetic properties were measured in vibrating sample magnetometers at room temperature and 4.2 K. The nanocrystalline composite alloys obtained as a result of the milling contained FeO and α-Fe with an average crystallite size of 15-20 nm as well as an amorphous phase, which was identified as a solid solution of oxygen in iron. However, alloys subjected to subsequent annealing contained only α-Fe and Fe₃O₄ with an average crystallite size of about 20 nm. Unlike the starting materials the produced powders had properties which are characteristic of hard magnetic materials. For example, the powder produced by the milling of Fe₂O₃+50% α-Fe mixture followed by annealing had the following properties at 300 K: intrinsic coercive force μ₀ H _c = 0.067 T, remanence B _r = 0.48 T, energy product (BH)_max = 9 kJ/m³.     

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.     

Evolution of Magnetocaloric Behavior in Oxygen Deficient La2/3Ba1/3MnO3−δ Manganites

Effects of oxygen deficiency on the thermomagnetic properties of La_2/3Ba_1/3MnO_3?δ polycrystalline perovskites have been predicted. By the help of the phenomenological model, the temperature dependences of the magnetization for La_2/3Ba_1/3MnO_3?δ with δ=0.0, 0.02, 0.05, 0.08, and 0.1 upon 1 T magnetic field were simulated. The behavior of the temperature dependent magnetocaloric effect, in the vicinity of magnetic phase transitions, was investigated. The magnetic entropy change, specific heat, and adiabatic temperature change for several δ were obtained. The values of maximum magnetic entropy change, full-width at half-maximum, and relative cooling power, in 1 T magnetic field variation, were calculated. As the oxygen content increases, the magnetocaloric effect of La_2/3Ba_1/3MnO_3?δ , decreases and shifts to room temperature. The results obtained show a strong dependence on the oxygen deficiency of the materials. The magnetocaloric effect of these materials is large and tunable, suggesting a possible technical application of the materials at moderate magnetic fields near room temperature. It is shown that for La_2/3Ba_1/3MnO_3?δ , the magnetic entropy change and adiabatic temperature change follows a master curve behavior.     

Synthesis and characterization of nanosize CoxNi1−xFe2O4 powders by glycothermal process

Nanosized Co_xNi_1−xFe₂O₄ powders were prepared in ethylene glycol solution under mild temperature and pressure conditions by precipitation from metal nitrates. The average size and distribution of the synthesized Co_xNi_1−xFe₂O₄ powders was about 15 nm and narrow, respectively. The magnetic property of the synthesized Co_xNi_1−xFe₂O₄ powder was about 60 (emu/g) with superparamagnetic character at room temperature.     

Morphology, Structural, Magnetic, and Magnetocaloric Properties of Pr0.7Ca0.3MnO3 Nanopowder Prepared by Mechanical Ball Milling Method

A sample of Pr_0.7Ca_0.3MnO₃ nanopowder was prepared by the ball milling method. The crystal structure examined by X-ray powder diffraction indicates that the sample is single phase and crystallizes in the orthorhombic perovskite system with Pnma space group at room temperature. The average crystallite size of 29 nm was obtained by X-ray diffraction. Magnetic measurements showed that the sample exhibits a ferromagnetic-to-paramagnetic transition at a Curie temperature close to 120 K. The magnetic entropy change |ΔS _M | has been deduced by the Maxwell relation method. The maximum value of the magnetic entropy change $\vert \Delta {S}_{M}^{\max} \vert$ obtained from the M(H) plot data is found to be 0.86 J/kg?K for an applied magnetic field of 2 T. At this value of magnetic field the relative cooling power (RCP) is 44.05 J/kg. At low temperature, large change in magnetic entropy has been observed in the sample. Our result on magnetocaloric properties suggests that Pr_0.7Ca_0.3MnO₃ nanopowder is attractive as a possible refrigerant for low-temperature magnetic refrigeration.