Study Of The Magnetic Properties And Electronic Structure Of Core-shell Nanoparticles

There has been intensive research on nanoparticles both experimentally and theoretically because of their technological applications in recent years. Being different from the bulk materials, nanoparticles often exhibit size-dependent properties. As the size decreases, the particle has a bigger surface area to volume ratio, leading to changes dramatically in chemical and physical properties. Compared with simple nanoparticles, core-shell nanoparticles have many novel properties and are applied broadly in the biomedical and the electronic field. They may be applied in targeted drug delivery, biosensors and high density magnetic recording.Based on Monte Carlo simulation the magnetic properties of a hexagonal prismatic nanoparticle consisting of a ferromagnetic core of spin-1 surrounded by a ferromagnetic shell of spin-3/2 with ferrimagnetic interface exchange coupling have been investigated. Curves of magnetizations, magnetic susceptibilities, phase diagrams, step effect, hysteresis loop, internal energy and specific heat of the system are obtained and discussed in detail. It has shown that exchange couplings and single-ion anisotropies of core and shell sublattice play important roles in magnetic properties of the system. A number of characteristic types of magnetization curves have been plotted. The occupation of shell sublattice by spin-3/2 results in the different initial values of total magnetization. For the appropriate parameters, the nanoparticle may exhibit compensation behavior. Especially, two compensation temperatures have been found in this system. The number of the magnetization plateaus varies for a series of different single-ion anisotropies of core and shell sublattice. The shape and number of the hysteresis loop can be changed depending on the value of exchange coupling, single-ion anisotropy and temperature. The phase temperature corresponding to the inflection point of the internal energy changes for various parameters.In addition, based on the first principle, this article using the VASP software studies the electronic structure and magnetization of Ni@Co core-shell nanoparticle. Calculation results show that the total magnetization of the system is 120.46μB, the average magnetization of Co atom is about 1.5μB, and the average magnetization of Ni atom is about 0.5μB. The band gap does not exist near the Fermi energy explains that the system is metallic. The maximum value of spin up state density and spin down state density appears in-2eV and-3eV, respectively, which explainsthat the corresponding band is most dense in these two kinds of energy. Partial wave state density of Co and Ni show that the greater density mainly comes from the contribution of respective d orbital. Charge density difference shows the charge transfer between Co and Ni on the core-shell border. The bond energy between part Co and Ni can be large.