![]() ![]() While there is vast literature on this enhancement of in finite and infinite systems (for a review see ), less attention has been paid to Ising model formulation in pair approximation (PA) for the appearance of EB in NPs systems. Within the mean-field-type calculations, a shift of the hysteresis loop along the magnetic field axis was accompanied by an enhancement of the coercivity. On the other hand, a variety of experimental facts associated with EB for the coupled FM/AFM layers were modeled as Ising-type system due to their strong uniaxial anisotropy. From the cooling field strength versus EB field ( ) and coercive field ( ) variations, their simulations have shown that the asymmetry in the hysteresis loops was due to the different magnetization reversal mechanisms in two branches related to exchange coupling at the FM/AFM interface. In order to understand the origin of the loop shifts displayed numerically in NPs with core-shell morphology, the researchers simulated, using the Monte Carlo (MC) technique, the atomic-scale modeling where the spins interact with nearest-neighbor Heisenberg interactions. However, only very recently, some works partially addressing the numerical studies of EB effects in magnetic NPs have been published. In particular, the temperature and size dependence of EB in FM/AFM nanoparticles (NPs), including commonly FM (core)/AFM (shell) interface, has attracted a lot of attention. Most of the subsequent studies have been focused on exchange-biased nanostructures composed of FM/AFM interfaces because of their technological applications in advanced magnetic devices. Since then, it was observed in many different systems containing FM/AFM interfaces, such as layered thin films, inhomogeneous materials, and small particles. The anisotropy was first discovered by Meiklejohn and Bean. It is one of the phenomena associated with the exchange anisotropy created at the interface between ferromagnetic (FM) and antiferromagnetic (AFM) spin structures. The exchange-bias (EB) phenomenon is defined as shift of the hysteresis loop along magnetic field ( ) axis, in either negative or positive direction. The observed coercivity and EB in NPs originated from nonzero odd coupling energies and their dependence on temperature ( ) and particle size ( ) are also discussed in relation to experimental findings. Shifted hysteresis loops with an asymmetry and coercivity enhancement are observed only in the presence of the odd interaction term in the Hamiltonian expression and their magnitudes show strong dependence on the value of. We have used a spin-1 Ising model Hamiltonian with dipolar (bilinear, ), quadrupolar (biquadratic, ), and dipolar-quadrupolar (odd, ) interactions in pair approximation to investigate the exchange-bias (EB), coercive field, and asymmetric hysteretic shearing properties peculiar to core/surface ( ) composite nanoparticles (NPs). ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |