Results 1 - 10 of 152
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[en] In this work, using the ab-initio calculations, we have investigated the phantom magnetism when the diamagnetic solids, carbon and nitrogen with d doped CdTe. We have applied in these calculations the combination between the Korringa-Kohn-Rostoker and coherent potential approximation method within the local density approximation and generalized gradient approximation (GGA). In this study, the doped compound presents a metallic behavior for both the approximations characterized by a small moment of about 0.299/0.326 and 0.249/0.266 μ for 24% of C and N, respectively. The polarization has shown a low and decreasing value from 43.73/59.56 to 0.29/2.26% for 9% and 24% of C impurity concentration, respectively. Unlike for the case of N, this parameter varies from 76.7/72.86 to 85.29/83.63% for 9% and 24% concentration, respectively. In addition, we have determined the mechanism of ferromagnetic coupling for the C- and N-doped CdTe. Furthermore, the stability of the compound is investigated by comparing the energy difference between the spin glass and ferromagnetic states. It is found that below the percolation threshold, contrary to the case of doping by N except for 20% using GGA, the C impurities lead to the most ferromagnetic stable phase. While the system changes its stability above this threshold when doped by the C impurities. Finally, we have estimated and discussed the Curie temperature using the mean field approximation.
[en] Recently, a reversible and a giant rotating magnetocaloric effect has been pointed out in the multiferroic TbMnO single crystal, opening the way for new designs of low-temperature magnetic cooling. In this paper, we report a preliminary theoretical work with the aim of enlarging our understanding on the electronic, magnetic and accordingly magnetocaloric features of the TbMnO compound. Particularly, the TbMnO magnetic anisotropy is analyzed in terms of X-ray magnetic circular dichroism (XMCD) and X-ray absorption spectroscopy (XAS) spectra.
[en] By means of the Monte Carlo method, we have simulated the mixed-spin-1/2 and spin-2 Ising ferrimagnetic system on a honeycomb lattice. We studied the variations of the magnetization as functions of the crystal field and the temperature and obtained the phase diagram of the system for various crystal field values. We have found that the system cannot display a point of compensation if we consider only nearest-neighbor interactions and the crystal field effect. Also, the tricritical point does not exist. To the best of our knowledge, this system has never been studied using the Monte Carlo method.
[en] In this paper, we used the ab-initio calculations, based on the Korringa-Kohn-Rostoker (KKR) method combined with the coherent potential approximation (CPA), to simulate the magnetic properties of ZnO, doped and co-doped with manganese and carbon, respectively. For this purpose, we have used two different approximations: the Local Density Approximation (LDA) and the Local Density Approximation-Self-Interaction Correction (LDA-SIC). Numerical results are presented for the compound Zn1 − 0.06Mn0.06O1−xCx when doping and co-doping is performed with Mn and C as doping elements. Total and partial DOSs are given for different concentrations using the two approximations, LDA and LDA-SIC. It is found that for 6% with doping by Mn the system becomes magnetic. The co-doping with carbon changes the behavior of the system : it becomes also magnetic for 4, 6 and 10% concentrations within both, LDA and LDA-SIC approximations. Furthermore, we have discussed the type of mechanism of exchange interaction and found that the double exchange is responsible for the appearing magnetism in the system, within the LDA and p-d interaction for LDA-SIC approximation. For 10% of carbon, we have found that the critical temperature approaches 280 K in the LDA approximation solely; and is about 305 K in the LDA-SIC approximation.
[en] In this work, a successful synthesis of magnetic cobalt ferrite (CoFe2O4) nanoparticles is presented. The synthesized CoFe2O4 nanoparticles have a spherical shape and highly monodisperse in the selected solvent. The effect of different reaction conditions such as temperature, reaction time and varying capping agents on the phase and morphology is studied. Scanning transmission electron microscopy showed that the size of these nanoparticles can be controlled by varying reaction conditions. Both X-ray diffraction and energy dispersive X-ray spectroscopy corroborate the formation of CoFe2O4 spinel structure with cubic symmetry. Due to optimized reaction parameters, each nanoparticle was shown to be a single magnetic domain with diameter ranges from 6 to 16 nm. Finally, the magnetic investigations showed that the obtained nanoparticles are superparamagnetic with a small coercivity value of about 315 Oe and a saturation magnetization of 58 emu/g at room temperature. These results make the cobalt ferrite nanoparticles promising for advanced magnetic nanodevices and biomagnetic applications.
[en] The structural electronic and magnetic properties of Ga doped delafossite CuFe0.96Ga0.04O2 are investigated using first principle calculations and Monte Carlo simulation. The calculations are based on the density functional theory using the Wien2k package within full potential linearized augmented plane wave method and spin-polarized generalized gradient approximation of the exchange-correlation functional. The simulated results show that an ideal Ga doped delafossite is an antiferromagnetic and the magnetic moments of the iron is about . Furthermore, we have explored the spin coupling interactions up to third nearest neighbors as well the coupling between adjacent layers in order to examine the magnetism and thermodynamical properties. In addition, we have reported the magnetic properties of this element using Monte Carlo simulation. The obtained values of the Néel temperature decrease as the absolute value of the single ion anisotropy increases. This result is in fair agreement with experiment.
[en] We report in this paper the impact of copper oxide (CuO) on the structural, magnetic, and magnetocaloric properties of Pr2/3Sr1/3MnO3 (PSMO) material. Our samples were synthesized by conventional solid-state reaction. The phase formation with no impurities was verified using the X-ray diffraction (XRD). The magnetic properties measured by Magnetic Properties Measurement System (MPMS) show the impact of the AFM CuO semiconductor on the magnetization and the transition temperature of the composite. The magnetic entropy changes were calculated from the isothermal curve of the magnetization as a function of the magnetic field. It is found that a small amount of copper oxide is enough to enhance the magnetocaloric properties of our materials.
[en] Novel spinel neodymium-tin ferrite nanoparticles (Nd0.5Sn0.5Fe2O4) have been synthesized by the coprecipitation method; x-ray diffraction (XRD), transmission electron microscopy (TEM), and superconducting quantum interference device magnetometer (SQUID) techniques were used to characterize the crystal structure, morphology, and magnetic properties. The spinel structure of a single phase is obtained according to XRD results. From TEM characterization results, we obtained a spherical morphology with an average of 13 nm. Magnetic measurement indicates that the nanoparticles have a superparamagnetic phase with a corresponding blocking temperature (TB) of about 360 K. These new nanomaterials can potentially be used in nanoelectronic devices, magnetic sensors, and hyperthermia application.
[en] Magnetocaloric effect on SrFe12O19 ceramic have been studied using Monte Carlo simulation. The thermal magnetization, dM/dT, magnetic entropy, and the specific heat of SrFe12O19 ceramic are obtained for several magnetic fields. The temperatures dependence of the magnetic entropy and of the adiabatic temperature for a several magnetic field have been obtained. The field dependence of relative cooling power (RCP) of SrFe12O19 ceramic has been determined for a several magnetic fields. The magnetic hysteresis cycle of SrFe12O19 ceramic has been obtained for a several temperatures. The obtained values are close to the experimental values. The transition paramagnetic to ferromagnetic is found at the Curie temperature. The second phase transition is also obtained around the Curie temperature.
[en] We use standard Monte Carlo simulations based on the Metropolis algorithm and mean-field calculations to investigate the magnetic properties of an Ising bilayer film consisting of two superposed ferromagnetic squared lattices A and B whose magnetic atoms have spin 7/2 and 5/2 respectively. Crystal-field and external magnetic field effects on the spins are considered in the model. The magnetic order parameters and response functions are calculated as functions of the temperature for selected values of the model parameters and this enables one to devise thermal phase diagrams by both methods. Our calculations only reveal second-order phase boundaries. Under appropriate conditions, compensation point phenomena are detected in the calculations below the critical temperatures. When the system is exposed to the external magnetic constraint, attracting hysteresis phenomena are sometimes generated. The temperature dependence of the coercitive field for various values of the crystal-field is singled out.