Papers by Keyword: Magnetization

Abstract: This research work instrumentalizes comprehensively the impacts of independent parameters like surface pressure, external magnetic field, and temperature on statistical thermodynamic quantities free energy, magnetization, occupied surface fraction, and equilibrium length. We approached it differently from a theoretical investigation conducted dealt with the behavioral dependence of surface parameters. Our mechanism was to investigate the interrelation between two dependent variables under exposure to two or more different independent parameters. Thus it seems complicated but it is used to probe surface information from the system at the same pace. We investigated the thermal excitation effect that leads to the detachment of the electron gas in contact with each occupied surface site, which reduces the adsorption of the surface in contrary external magnetic fields and pressure enhances the occupied surface probability of electrons to contact surface sites. Our findings reveal that the solid GaAs surface tends to capture electrons under the influences of external magnetic fields and pressure thus binding electrons and putting additional confining potential meanwhile the surface properties are affected. On the other hand surface, free energy has an inverse relation with magnetization, occupied surface fraction, in the case of equilibrium length it depended on the strong external magnetic fields.

Abstract: In the present work, we have synthesized x [Co_0.9Ni_0.1Fe₂O₄]-(1-x) [0.5Ba_0.7Ca_0.3TiO₃-0.5BaZr_0.2Ti_0.8O₃], x = 0.3, 0.4 & 0.5 multiferroic composite by hydroxide co-precipitation method. The structural and morphological analysis of the composite was carried out by using X-ray diffraction and Scanning Electron Microscopy. The XRD spectra confirm the perovskite phase and spinel phase. Dielectric properties of the composite were studied using Impedance analyzer. The variation of dielectric constant and loss of tangent (Quality factor) in the frequency range of 100 Hz to 1 MHz were investigated. Magnetocapacitance were measured for magnetic field up to 1 Tesla, which increases with increase in magnetic field. Dielectric constant possesses contribution due to magnetic field dependent interfacial polarization and variation due to induced stress which can be explained on the observed MD effect. Saturation magnetization of composites increases with increase in CNFO content.

Abstract: Nitrides of ‘2:17’ - type based on rare earth metals and iron are of interest as promising magnetic materials for the development of high-energy permanent magnets. The magnetic properties and phase composition of the starting compound Sm_1.8Er_0.2Fe₁₇, nitride Sm_1.8Er_0.2Fe₁₇N_2.1 and its crushed powders have been investigated. The magnetic measurements of the samples were studied in magnetic fields up to 70 kOe at room temperature. It was found that the introduction of nitrogen atoms into the crystal lattice of the substituted composition (Sm,Er)₂Fe₁₇ in combination with the effect of high-energy milling of nitride leads to an increase in the saturation magnetization (σ_S) and coercive force (H_C).

Abstract: Magnetic properties of the R₂Fe₁₇ compounds are sensitive to the atomic substitutions and interstitial absorption of nitrogen. In our work, both were combined and their effect on the magnetization behavior of Er₂Fe₁₇ compound in magnetic fields up to 58 T was studied. Er₂Fe₁₇N₂, Sm_1.2Er_0.8Fe₁₇N₂ and Sm_1.8Er_0.2Fe₁₇N_2.1 nitrides were prepared. Magnetization measurements were carried out, mainly on powder samples (excluding Er₂Fe₁₇ single crystal). Nanopowders of Sm_1.2Er_0.8Fe₁₇N₂ were obtained by mechanical grinding. The grinding time was varied from 0 to 60 minutes. The strength of the inter-sublattice coupling in samples is estimated by analyzing high-field magnetization data.

Abstract: The microstructure and magnetization of SmCo₅ micro-particles may be used as feedstock for 3D printing to make miniature strong magnets. Thus, the magnetic response and microstructures of commercially available SmCo₅ micro-particles were studied under various heat treatments using a high wattage laser. The magnetization of laser heat treated powders at 50-watt showed an increase in magnetization, while the 75-watt melt showed a little to no change. Unfortunately, the coercivity of both laser heat treated samples decreased significantly. Oxidation during the heat treatment is suspected to result in low coercivity. Purging with argon-gas prior to laser heating showed improved coercivity. To further minimize the oxidation problem a set of SmCo₅ powder was reduced prior to laser heat treatment using a constant flow of hydrogen gas while being heated at various temperatures from 100 oC to 400 oC for a period of ~4 hours. The results show that the magnetization generally increases with the temperature, while the coercivity decreases significantly. Another set of SmCo₅ was annealed in a vacuum furnace for one hour at temperatures between 200 oC and 400 oC in order to confirm that no hydride phases were formed during reduction. The magnetization and coercivity showed similar variations with annealing temperature to those for the reduced powders confirming that these variations may be due to change in crystal structure rather than formation of hydrides. X-ray Diffraction (XRD) studies were performed to identify the changes in crystal phases.

Abstract: Bismuth ferrite (BiFeO₃) nanoparticles has been synthesized by coprecipitation method with various NaOH concentration (4, 6, 8, and 10 M) and temperature (RT, 60, 80, and 100 C). X-ray diffraction patterns showed the emergence of Bi(OH)₃ and Bi₂₅FeO₄₀ structures with crystallite size in the range of 15.1 nm to 35.6 nm. The particles sample was agglomerated. Hysterisis loop showed the linear M–H loops behaviour with no magnetization saturation in 15 kOe maximum field applied which indicates the antiferromagnetic properties. The coercivity field tends to increase by the increasing of the NaOH concentration and synthesis temperature. In addition, the annealing treatment could leads the increasing of coercivity fields while decreasing the magnetization of BFO sampel.

Abstract: Effects of Mn-substitution on magnetic properties of Zn_1-xMn_xO (MZO) nanoparticles with x= 0.00, 0.03, 0.05 and 0.07 have been investigated along with their local structure. Study on Mn K-edge XANES spectra of MZO reveals that the oxidation state increases by Mn-substitution, which further implies that MZO exhibits a mixed valence state of Mn³⁺/Mn⁴⁺. The local structure analysis on Mn K-edge EXAFS spectra shows that the coordination number (CN) of Mn reduces by increasing Mn concentration, thus the amount of oxygen vacancy (V_O) increases by Mn-substitution. Interestingly, the magnetization of MZO also tend to increase as the Mn concentration increases. The M(H) curves exhibit a linear (paramagnetic) behavior, showing no evidence of room-temperature ferromagnetism. Our results show that magnetism of MZO is related to the correlation between Mn magnetic moment and V_O.

Abstract: In this paper, the magnetization reversal of sphere-shaped ferromagnetic nanoparticles has been investigated by means of micromagnetic simulation. Some ferromagnetic particles such as Cobalt, Iron, Nickel, and Permalloy were modeled with size variation from 50 nm to 100 nm. The discretization of the ferromagnetic model was used a cell size of 2.5×2.5×2.5 nm³ considering the exchange length (l_ex) of the materials. The quasi-static magnetic field was induced into the nanosphere to observe the magnetization response under time dependence. It is found that the coercivity values are decreased as the sphere size increased, which was conformed the experimental results. It is also observed that the domain structure of a single particle in remanent and ground-state condition are identical. Therefore, the specific understanding of magnetization process and domain structures in ferromagnetic nanoparticles could be an important step in the development of nanopatterned magnetic memory storage.

Abstract: Some studies of the usage of biomass to produce carbon-based compounds have been reported in the past. Here we report that palmyra sugar can be one of the sources to produce amorphous carbon (a-C) from biomass after the heating treatment at 250°C. In this paper, X-Ray Diffraction (XRD), Scanning Electron Microscopy-Energy Dispersive X-Ray (SEM-EDX), Fourier Transform Infrared (FTIR) and Superconducting Quantum Interference Device (SQUID) measurements are reported in order to check the detailed properties of a-C from palmyra sugar. The XRD data at a diffraction peak position (2θ) of ~23^o support the formation of a-C. The functional groups detected by FTIR spectra consist of C=C, C-C, C-O, C=O, C-H and O-H. The remnant magnetization (Mr), coercive field (Hc) and saturation magnetization are estimated as ~0.1 10^-3 emu/g, ~50 Oe and ~9 10^-3 emu/g, respectively. Soft ferromagnetism in a-C from palmyra sugar is confirmed, comparable with the magnetization result in the reduced graphene oxide (rGO) sample from coconut shell and rGO commercial material which have the same mixture hybridization. Some studies of the usage of biomass to produce carbon-based compounds have been reported in the past. Here we report that palmyra sugar can be one of the sources to produce amorphous carbon (a-C) from biomass after the heating treatment at 250°C. In this paper, X-Ray Diffraction (XRD), Scanning Electron Microscopy-Energy Dispersive X-Ray (SEM-EDX), Fourier Transform Infrared (FTIR) and Superconducting Quantum Interference Device (SQUID) measurements are reported in order to check the detailed properties of a-C from palmyra sugar. The XRD data at a diffraction peak position (2θ) of ~23^o support the formation of a-C. The functional groups detected by FTIR spectra consist of C=C, C-C, C-O, C=O, C-H and O-H. The remnant magnetization (Mr), coercive field (Hc) and saturation magnetization are estimated as ~0.1 10^-3 emu/g, ~50 Oe and ~9 10^-3 emu/g, respectively. Soft ferromagnetism in a-C from palmyra sugar is confirmed, comparable with the magnetization result in the reduced graphene oxide (rGO) sample from coconut shell and rGO commercial material which have the same mixture hybridization.

Abstract: Neodymium substituted yttrium iron garnet (YIG) nanoparticles with compositional variation of Nd_xY_3−xFe₅O₁₂ where x = 0.0, 0.2, 0.5 and 0.8 was prepared by mechanochemicals method using high energy milling (HEM). The characterization was done using X-rays diffractometer (XRD), scanning electron microscope (SEM), vibrating sample magnetometer (VSM) and vector network analyzer (VNA). It was found that the mechanical milling followed by sintering promotes the complete structural formation of the yttrium iron garnet (YIG) structure. The XRD patterns confirm the complete introduction of Nd³⁺ ion into the YIG with an addition of Nd doping concentration. nanocrystalline particles with high purity and sizes ranging from 0.12μm to 0.16μm were obtained. The magnetization value, M_s from all Nd-doped samples were obtained in the range between 34 to 37emu.g^-1. The magnetic coercivity (H_c) was achieved of 0.012kOe (12Oe) for the non-doped sample (YNd-0) and then increase with the addition of neodymium concentration. The increase in H_c for all the sample series can be attributed to an enhancement of the magnetocrystalline anisotropy with anisotropic Fe²⁺. The variation of the reflection loss (RL) versus frequency was observed in Nd doped YIG, Y_1-xNd_xFe₅O₁₂ with x = 0.0 – 0.8 in the frequency range of 7 –12 GHz. The optimum reflection loss (RL) was found to be 8.66(-dB) at 9.5GHz in Y_2.2Nd_0.8Fe₅O₁₂ (YNd-08) for x = 0.8.