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[en] Using Monte Carlo simulations, magnetic properties of the ferromagnetic nanoparticles of Ising spin-1 are investigated in the framework of the Ising model. The system is considered to have a Rubik’s cube structure composed of nanocubes having an equivalent exchange coupling, while, between adjacent nanocubes, the exchange coupling is assumed to vary. Both size effects and system parameters’ influence on phase diagrams of the nanosystem are studied. Thus, the magnetic properties of the system such as the critical temperature, the magnetization, and the coercive field are computed.
[en] Highlights: • We have studied the magnetocaloric effect of the metallic antiperovskite compound Mn3GaC. • We used the ab-initio calculations, the Monte Carlo simulations and mean field theory. • A second-order ferromagnetic-paramagnetic phase transition about TC ∼ 249 K. • The magnetic moment and the exchange coupling interactions are calculated. - Abstract: The structural, electronic, magnetic, and magnetocaloric properties of the metallic antiperovskite compound Mn3GaC were investigated using several theoretical methods such as: First principle calculations, Monte Carlo simulations and mean field theory. The metallic antiperovskite compound Mn3GaC exhibits a second-order ferromagnetic-paramagnetic phase transition around TC = 249 K. Using the first principle calculations, the magnetic moment and the exchange coupling interactions values are 1.37 μB and J1 = 35.78meV, J2 = 40.16meV, respectively. The total magnetization, the susceptibility and the specific heat of this compound are calculated. The critical temperature obtained is in good agreement with the experimental results. Obviously, the large MCE with no hysteresis loss is obtained around TC. The maximum values of the magnetic entropy change (ΔSmag), adiabatic temperature change (ΔTad) and the relative cooling power (RCP) are 13.41 J/kg.K, 15.96 K, 748 J/kg respectively, under applied an external magnetic field of h = 5.0 T.
[en] Using a composition of first-principle density functional theory (DFT) calculations and Monte Carlo simulation with the calculation within the self-interaction-correction local-density approximation, the electronic, magnetic, and optical properties of doped and co-doped GaN (Ga1−xCrxN, Ga1−xNixN) and GaN (Ga1−2xCrxNixN) (x = 0.03 and 0.06), respectively, have been investigated. Our results have proven that the half-metallic ferromagnetic state still persists of co-doped GaN. In comparing the total energies, ab initio calculations certify the magnetic-state stability of the ferromagnetic phase compared with the spin-glass state. The exchange interactions obtained from the ab initio calculations were used as input parameters in a classical Ising model by Monte Carlo simulation to confirm the half-metallic ferromagnetic states with high Neel temperature.
[en] The half-metallic ferromagnetic behavior of rare-earth nitride Gd0.95 TM0.05N (TM = Ti, V, Cr, Mn and Co), based on diluted magnetic semiconductors (DMSs), is investigated using the Korringa–Kohn–Rostoker (KKR) method combined with the coherent potential approximation (CPA) within a framework of density functional theory (DFT). The energy difference between the ferromagnetic and disorder local moment states has been evaluated. The exchange interactions obtained from first-principles calculations resulted in ferromagnetic states with Curie temperatures within the ambient conditions. Moreover, the optical absorption spectra obtained by ab initio calculations confirm the ferromagnetic stability based on the charge state of magnetic impurities.
[en] SnO2:TM (V, Cr, Mn and Fe) based dilute magnetic semiconductors are investigated within self-interaction-corrected local density approximation (LSDA-SIC) from first-principles calculation. LSDA-SIC results are compared with the calculated ones within standard LSDA, the stable magnetic state of the system is evaluated by comparing the total energies of ferromagnetic state and spin-glass state. The Ferromagnetic and half metallic behaviors was observed and conformed with the local-moment-disordered state energy for LSDA and LSDA-SIC approximation in [Sn 0.95 TM 0.05 (V, Cr, Mn and Fe)]O2. The exchange interactions obtained from first principle calculations and used in a classical Ising model by a Monte Carlo approach resulted in ferromagnetic states with Curie temperatures within the ambient conditions.