Electrical and magnetic properties of NdCuPb compound

Electrical and magnetic properties of NdCuPb compound were investigated by means of electrical resistivity, magnetization measurements in the temperature range 1.5–100 K. Low-field dc susceptibility goes through a maximum at T_N=13.2  K, indicating a paramagnetic to an antiferromagnetic transition and then follows a sharp peak at T=5.9  K. The susceptibility data exhibits a Curie–Weiss like behavior in the paramagnetic regime and the effective moment per neodium atom is found to be 3.62μ_B from the data at temperatures above 42 K. This value is exactly equal to that for Nd³⁺, while at lower temperatures, the data yields a little bit less than its free ion value. The ratio M/H versus temperature T curves for different values of the magnetic field split into multiple branches at about T=42  K due to crystalline field effects.In addition, electrical resistivity in a magnetic field up to 120 kOe was also measured in the same temperature range. The resistivity gives non-metallic behavior. The antiferromagnetic transition is clearly discern by a “Cr-like” anomaly at about 13 K, followed by a sharp increase in the resistivity (like a jump) at T=5.9  K where the susceptibility gives similar effect. On other hand, the magnetic contribution to the resistivity begins to decrease at T=42  K at which M/H curves merges. All these behavior may be attributed to crystal-field-splitting of neodium atoms’levels.     

磁化可提高酸化效果

进行了一系列磁化酸化液的实验室研究。结果表明,磁化能减慢酸液与碳酸盐岩石的反应速度。在首次进行的生产性试验中,取得了良好效果。     

磁处理对水泥浆流动性的影响

文中介绍了水泥浆磁处理后流动度、剪切应力、视粘度、稠度等参数的变化,并对应用机理进行分析研究。结果表明,磁处理可使水泥浆剪切应力、视粘度、稠度降低,流动度增加,流性指数增加,明显改善水泥浆流动性,有利于提高顶替效率和提高固井质量。     

Synthesis,composition and spin-dynamics of FCC and HCP phases of pyrolysis derived Co-nanoparticles embedded in amorphous carbon matrix

We report the structure, magnetic domain state and spin dynamics of biphasic Co nanoparticles embedded in amorphous carbon matrix. Two types of samples were synthesized by heating the precursors (Co-acetylacetonate and toluene) from RT to the pyrolysis reaction temperature (800 °C) at two different heating rates, viz. ∼ 3 °C/min and ∼20 °C/min. We observe that the sample prepared at higher heating rate (∼20 °C/min) predominantly contains fcc-phase of Co in the Co-nanoparticles, whereas the sample synthesized at lower heating rate exhibits higher amount of the hcp-phase-content in the Co-nanoparticles. The Co-nanoparticles are surrounded by graphitic carbon layers forming core-shell type morphology. The hcp-phase of Co is characterized by a higher saturation magnetization and coercivity (higher magnetic hardness) than the fcc-phase. The nature of the measured hysteresis loop in combination with the estimated critical size for the particles to be in a single magnetic domain state suggest that both hcp and fcc-phases of Co coexist in the same particle and most of the particles are multidomain-particles. Furthermore, our results reveal that the dynamics of the spins present at the grain boundaries are the slowest followed by those in the fcc-phase and hcp-phase of Co. The dynamics of the spins present at the domain walls are slower than those inside the magnetic domains. The responsive nature of the spins on the domain walls in comparison to those inside the domains leads to the so called domain wall enhancement effect.     

Nb modified structural,magnetic and magnetocaloric properties of double perovskite Ba2FeMo1−xNbxO6

A systematic study focusing on the effect of Niobium (Nb) doping on the structural, magnetic and magnetocaloric properties of Ba₂FeMoO₆ samples is presented here. The samples of interest Ba₂FeMo_1?xNb_xO₆ (0 ≤ x ≤ 0.4) were prepared using the solid state reaction method and were confirmed to possess a cubic structure with Fm-3m space group using the X-ray diffraction analysis and Rietveld refinement. A second order of ferromagnetic phase transition was recorded in both the pure as well as the Nb doped samples using the temperature dependent magnetization and Arrott plots analysis. The pristine Ba₂FeMoO₆ (BFMO) sample indicated a spontaneous magnetization (34.6 emu/g at 100 K) with a relatively sharp magnetic transition at the Curie temperature (T_C) of 315 K as compared to the doped samples. A magnetic entropy change of 0.93 Jkg^?1K^?1 at an applied magnetic field of 2.5 T was measured for the pure BFMO sample. The doped BFMO samples with Mo partially substituted by Nb however, were observed to effectively modify the T_C accompanied by a decrease in magnetization. The results investigated in this work suggest that the magnetic and magnetocaloric properties of the BFMO can be tailored by controlled Nb doping which is of significant importance in order to realize the numerous potential applications of the material in the magnetic refrigeration technology.     

Microstructure,magnetic and optical properties of Nb3+ and Y3+ ions co-substituted Sr hexaferrites

Series of SrNb_xY_xFe_12-2xO₁₉ (0.00 ≤ x ≤ 0.05) hexaferrites (HFs) were fabricated via citrate sol-gel approach. Structural and magneto-optical properties of ensembles were investigated in detail. The structural and morphological analyses revealed the formation of M-type Sr hexaferrite nanoparticles. Diffuse reflectance data were registered to estimate the direct optical energy band gaps (E_g) in a range of 1.77 eV-1.87 eV. Room temperature (RT, 300 K) and low temperature (10 K) magnetic hysteresis curves were recorded by enforcing applied dc magnetic field up to ±70 kOe. Magnetic parameters were significantly tuned due to coordination of Nb³⁺ and Y³⁺ rare earth ions. Specified magnetic data reveal the strong ferromagnetic characteristics of pristine SrFe₁₂O₁₉ and co-doped HFs with Nb³⁺ and Y³⁺ ions at both temperatures. RT squareness ratio (SQR) has an exception only for pristine sample as 0.506, which is in the margin of theoretical limit assigning the single-domain nature with uniaxial anisotropy. However, all co-doped samples have SQR = 0.288–0.485 values that are smaller than theoretical limit of 0.50, implying multi-domain nature at RT and at 10 K. Co-doped ions cause lowering in super-exchange interactions between different sites and resulting the decrements of intrinsic magneto-crystalline anisotropy and coercivity fields. The specified magnetic characteristics make our fabricated SrNb_xY_xFe_12-2xO₁₉ (0.00 ≤ x ≤ 0.05) HFs good candidates as permanent magnets applications and high-density recording media.     

Sol-gel synthesis,structural, morphological and magnetic properties of BaTiO3–BiMnO3 solid solutions

In this study, solid solutions of (1-x)BaTiO₃-xBiMnO₃ have been synthesized by an aqueous sol-gel method. It was determined that single-phase compounds can be obtained up to x = 0.6 and with further increase in percentage of BiMnO₃ component additional crystal phases were detected. Perovskite crystal structure was determined for all synthesized compounds regardless of chemical composition. Raman spectra of synthesized solid solutions showed gradual change of the shape with an increase of BiMnO₃ fraction. It was demonstrated that partial substitution of BaTiO₃ by BiMnO₃ led to the drastic growth of grains of the end products. Magnetization measurements showed that all BiMnO₃-containing samples are characterized by paramagnetic behavior. Clear correlation between magnetization values and composition of the materials was observed, magnetization values increased with increasing of BiMnO₃ content in solid solutions.     

Grain growth kinetics and magnetic properties of a V-doped ZnO dilute magnetic oxide

Zn_0.95V_0.05O ceramics, elaborated from milled ZnO and V₂O₅ nanopowders, were sintered at 900, 1000 and 1100 °C for 1, 2, 4, 6, 10 and 14 h. The growth kinetics was studied identifying the grain growth exponent, the activation energy and the pre-exponential factor. The high V₂O₅ concentration allowed a rapid grain growth at 900 °C only at the very first stages (t < 1 h). Meanwhile, at temperatures of 1000 and 1100 °C, the grain growth was extremely fast with a growth exponent of 0.72. The magnetic properties of the samples indicate that ferromagnetism exist in all samples in different magnitudes depending on the sintering conditions. In particular, the maximum magnetization was obtained on the sample sintered at 1100 °C for 14 h, despite the reduction of V concentration. Additionally, secondary paramagnetic phases were detected in the samples sintered at lower temperatures and shorter sintering times.     

Microwave absorption properties of CoGd substituted ZnFe2O4 ferrites synthesized by co-precipitation technique

A series of co-precipitated Zn_1?xCo_xGd_yFe_2?yO₄ spinel ferrites (x = 0.0–0.5, y = 0.00–0.10) sintered at 1000 °C were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), vibrating sample magnetometery (VSM) and microwave cavity perturbation (MCP). XRD patterns and FTIR spectra reveal formation of the spinel phase along with few traces of GdFeO₃ second phase. The lattice constant decreases with an increasing amount of CoGd ions due to the segregation of Gd³⁺on the grain boundaries and due to replacement of lager Zn²⁺ ions with smaller Co²⁺ ions. SEM shows grain size to decrease with the increase of CoGd contents due to grain growth inhibition by the second phase. VSM results show remanence and saturation magnetization to exhibit an increasing trend due to Co substitution on octahedral sites and presence of a second phase. The coercivity increases with the increase of CoGd contents due to anisotropic nature of Co. MCP shows the complex magnetic permeability to increase with CoGd concentration while the complex permittivity decreases.     

Effect of Sm doping on structure,dielectric and magnetic properties of GdFeO3

Nano-particles of GdFeO₃ (GFO) and Gd_0.4Sm_0.6FeO₃ (GSFO) were synthesized by sol-gel auto-combustion method to study the effect of Sm³⁺doping on physical properties of GFO. Rietveld refinement of x-ray diffraction pattern confirms the proper phase formation of samples and the average octahedral <Fe–O1–Fe> angle of GSFO is found to be 145.54⁰ which is larger compared to GFO 142.53⁰. Temperature dependent DC magnetization measurements showed that Sm doping in GdFeO₃introduces spin-reorientation transition which is absent in pure GdFeO₃ phase. The dielectric constant of GSFO is found to be larger than that of GFO because of change in hybridization between the O-2p states and Fe-3d states. In both the ceramics at higher temperatures (above 150 °C) conduction mechanism is taking place via oxygen defect charge carrier hoping. The complex impedance analysis revealed that the distribution of relaxation time of charge carriers is temperature independent. Sm doping in GFO not only changed the dielectric properties but also changed the magnetic coercive field and shape of the magnetic isotherm of GFO.