Manganese doped gallium oxynitride prepared by nitridation of citrate precursor

Manganese doping of gallium oxynitride was investigated to obtain a magnetic semiconductor by nitriding a precursor in ammonia flow. The precursor was obtained by prefiring a mixed gel made of Mn²⁺ and Ga³⁺ nitrates and citric acid in aqueous solution. The products were isostructural with hexagonal GaN. The doping limit was 10 and 5 at% in the samples nitrided at 750 and 850 °C, respectively. Chemical analysis of the products suggested that they were manganese doped gallium oxynitrides. Oxide and nitride ions were randomly distributed in the anion sites in the latter product. Manganese oxide cluster might be formed in the former. The product nitrided at 850 °C showed an antiferromagnetic interaction with a Weiss temperature θ = −38 K, while the product nitrided at 750 °C was paramagnetic.     

Magnetic study of Ti-substituted NiFe2O4 ferrite

The Ni_1+xTi_xFe_2−2xO₄ (0 ≤ x ≤ 0.1) ferrite systems prepared by a semi-chemical route, have been studied by electron paramagnetic resonance (EPR) at X-band, Mössbauer spectroscopy and magnetization measurements at various temperatures. EPR spectra of these samples comprise generally a broad and asymmetric EPR signal. The variation of g_eff and peak-to-peak line width ΔH_pp, with Ti concentration and temperature are attributed to the variation of dipole–dipole interaction and the superexchange interaction. Mössbauer spectra comprise two sets of sextet attributed to Fe³⁺ at two distinct sites-A and -B. Ti⁴⁺ ions are concluded to occupy the octahedral B-sites. Magnetic moment is found to decrease with the increase of Ti⁴⁺ concentration. The effective magnetic field H_eff at the A-sites also follows a similar trend. The reason is attributed to the canted structure of spins in the Ti-doped samples. An anomalous behavior at x = 0.015 is observed in the properties studied here and some sort of phase change is believed to occur at 473 K in these ferrites.     

Structural,magnetic, electrical and microwave properties of spinel ferrites

The ferrite series having formulation SrYb_yFe_2–yO₄ (y = 0.00 to 0.10) were synthesized via the sol–gel procedure. The involvement of the yttrium in the base produces several changes in the structural, magnetic, and electrical performance of the system. Investigation of structural parameters was done through X-ray diffraction. All samples have cubic structures confirmed from X-ray diffraction. The coercivity of sample enlarges with the involvement of Yb-ions while their saturation and remanence magnetization values drop. When the concentration of Yb-ion increases in the lattice, the real and imaginary values of permittivity reduce. The increased content of Yb enhances the impedance value. The analysis of the M vs H loop was finished under the fixed range of ?2 to +2 kOe. By using 0.5–12 GHz frequency, the microwave measurements of all the sample were performed. The dispersion of frequency of ferrites is responsible for the natural magnetic resonance phenomenon and the domain wall pinning. The evaluated features of synthesized sample show their appropriateness for microwave absorption appliances.     

Effects of synthesis route on the structural,magnetic and magnetocaloric properties of Pr0.8K0.2MnO3

Pr_0.8K_0.2MnO₃ ceramics are prepared by solid-state reaction and Pechini sol–gel method. The influence of the powder synthesis method on the structural, morphological, magnetic and magnetocaloric properties of the samples are investigated. The X-ray diffraction pattern shows reflections typical of the perovskite structure with orthorhombic symmetry. The experimental results reveal that both samples undergo a second-order phase transition. The maximum magnetic entropy changes, deduced from the M–µ₀H measurements, are 3.77 and 7.23 J/kg K under the magnetic field change of 5 T for Pr_0.8K_0.2MnO₃ synthesized by using solid-state reaction and sol–gel methods respectively. The field dependence of magnetic entropy change is analyzed showing the power law dependence, ΔS(T,µ₀H)=a(T)(μ₀H)^n(T,H) at the Curie temperature. Using the scaling laws of ∆S, the experimental ∆S collapse onto a universal curve for both ceramics. These results suggest that the physical properties of our samples are strongly depended on synthesis techniques. It is found that Pechini sol–gel method is more efficient and stable to obtain ceramic materials with good magnetic properties. Consequently, a substantial increase of the ferromagnetic to paramagnetic transition temperature and an enhancement of magnetocaloric properties are observed in the sol-gel made sample making it more suitable for magnetic refrigeration applications.     

Impact of Zn doping on the dielectric and magnetic properties of CoFe2O4 nanoparticles

Owing to its unique magnetic, dielectric, electrical and catalytic properties, ferrite nanostructure materials gain vital importance in high frequency, memory, imaging, sensor, energy and biomedical applications. Doping is one of the strategies to manipulate the spinel ferrite structure, which could alter the physico-chemical properties. In the present work, Co_1-xZn_xFe₂O₄ ($x$ = 0, 0.1, 0.2, 0.3, and 0.4 wt%) nanoparticles were prepared by sol-gel auto-combustion method and its structural, morphological, vibrational, optical, electrical and magnetic properties were studied. The structural analysis affirms the single-phase cubic spinel structure of CoFe₂O₄. The crystallite size, lattice constant, unit cell, X-ray density, dislocation density and hopping length were significantly varied with Zn doping. The Fe–O stretching vibration was estimated by FTIR and Raman spectra. TEM micrographs show the agglomerated particles and it size varies between 10 and 56 nm. The Hall effect measurement shows the switching of charge carriers from n to p type. The dielectric constant (ε′) varies from 0.2 × 10³ to 1.2 × 10³ for different Zn doping. The VSM analysis shows relatively high saturation magnetization of 57 and 69 emu/g for ZC 0.1 and ZC 0.2 samples, respectively than that of undoped sample. All the prepared samples exhibit soft magnetic behaviour. Hence, it can be realized that the lower concentration of Zn ion doping significantly alters the magnetic properties of CoFe₂O₄ through variation in the cationic distribution and exchange interaction between the Co and Fe sites of the inverse spinel structure of CoFe₂O_4.     

Magnetic and electrical transport properties of La0.5A0.5CoO3 nanoparticles (A = Sr, Ca, and Ba)

We have investigated the effect of particle size on the electrical transport and magnetic properties of La_0.5A_0.5CoO₃ (A = Sr, Ca, and Ba) nanoparticles synthesized by sol-gel technique. A size-induced metal to insulator transition is observed in the resistivity behaviour of Sr- and Ba-doped samples as the dimension changes from higher to lower ones. The magnetoresistance exhibits almost linear behaviour throughout the studied field range. The zero-field-cooled (ZFC) and field-cooled (FC) magnetizations display a broad paramagnetic to ferromagnetic transition at T_C with a large magnetic irreversibility. The magnetization results indicate that Co³⁺ ions are in the intermediate spin state but Co⁴⁺ ions stay in a mixture of intermediate and high spin states. The observed frequency dependent shoulder in the in-phase and the peak in the out of phase component of the ac susceptibility indicate the glassy nature of the samples. The analysis of the ac magnetization results suggests that the magnetic behaviour is consistent with the cluster glass model.     

强磁化钢领纺纱性能的试验研究

为了探讨强磁化钢领的纺纱性能,在涤棉、纯棉五个品种上,采用S6、S7型强磁化钢领与抛光钢领进行了纺纱试验,测试对比了成纱毛羽、强伸性能及条干水平等性能指标.结果表明,强磁化钢领纺纱质量优于抛光钢领,特别是改善成纱毛羽和强伸性效果明显.用闪光测速仪观察发现,钢丝圈在强磁化钢领比抛光钢领运行平稳,这可能是强磁化钢领能改善成纱质量的主要原因.     

Synthesis, characterization and magnetic properties of La added Mg-Cd ferrites prepared by oxalate co-precipitation method

Nanosized powders of Mg-Cd-La ferrite synthesized by oxalate co-precipitation method using high purity sulphates are presented. The powder has been characterized by X-ray powder diffraction (XRD), infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The phase identification of powder reveals biphasic nature of materials. The lattice constant, X-ray and physical density, porosity, crystallite size, site radii and bond length were directly affected by addition of rare earth ion (La³⁺) in Mg-Cd ferrite. The crystallite size of the samples lies in the range 25.67-30.55 nm. FT-IR spectra show two absorption bands in the frequency range from 3.5 × 10⁴ to 8.0 × 10⁴ m⁻¹ which are attributed to stretching vibration of tetrahedral and octahedral complex Fe³⁺-O²⁻ respectively. The addition of La³⁺ alters the characters of powder and decreases the grain size which suppresses the abnormal grain growth. The addition of La³⁺ resulted increase in saturation magnetization, remnant magnetization, 4πM_s and coercivity. Coercivity shows size dependent behavior. Such results are promising ones for high frequency applications.     

Structural, optical and electromagnetic properties of Bi1−xHoxFeO3 multiferroic materials

Bi_1−xHo_xFeO₃ (x = 0.00, 0.05, 0.10, 0.15 and 0.20) polycrystalline ceramics were synthesized by a solid-state reaction and their structural, absorption, Raman scattering, impedance and magnetic properties were investigated. The substitution of rare earth Ho for Bi was found to decrease the impurity phase in BiFeO₃ ceramics. There appears an anomalous change in the lattice constants, optical band gap as well as the impedance spectroscopy and magnetization of samples at x = 0.10, suggesting a limit of dissolubility of Ho doped ions in BiFeO₃. Additionally, the Raman measurement performed for the lattice dynamics study of Bi_1−xHo_xFeO₃ samples reveals a band centered at around 1000-1300 cm⁻¹ which is associated with the resonant enhancement of two-phonon Raman scattering in the multiferroic Bi_1−xHo_xFeO₃ samples. Ho-doped BiFeO₃ also showed a ferromagnetic-like behavior with M_r = 1070 × 10⁻⁴ and M_s = 1.60 emu/g for optimum content x = 0.10, which is similar to the solid solution system of BiFeO₃.     

Structural, magnetic and dielectric properties of Bi5−xLaxTi3Co0.5Fe0.5O15 ceramics

The Bi_5−xLa_xTi₃Co_0.5Fe_0.5O₁₅ (0 ≤ x ≤ 0.4) ceramics were successfully synthesized by a modified Pechini process. The samples were characterized by X-ray diffraction and no impurity phase has been detected. The cell volume of the composites increases monotonously with the increase of La content, which indicates that La ions have been incorporated into the lattice of Bi₅Ti₃Co_0.5Fe_0.5O₁₅. The magnetic measurements show that La doping on Bi sites has enhanced the magnetization of Bi_5−xLa_xTi₃Co_0.5Fe_0.5O₁₅ (0 ≤ x ≤ 0.4). Both the dielectric constants and loss tangent of all the samples decrease on increasing frequency and then become almost constant at room temperature. The La doped Bi₅Ti₃Co_0.5Fe_0.5O₁₅ samples exhibit improved dielectric and ferroelectric properties, with higher dielectric constant enhanced remnant polarization and lower losses at room temperature.