Spin lattice dynamics simulations of defective Fe crystals and NPs

DOS SANTOS G.; MEYER, ROBERT; APARICIO, ROMINA; BRINGA, E M; URBASSEK, HERBERT M.

Congreso; International Seminar on Condensed Matter Physics and Statistical Physics; 2021

Magnetic properties can be modified by defects. In this work we consider defects in both bulk and nanoparticle (NP) samples of b.c.c. Fe, using classical coupled spin-lattice dynamics. This simulation technique is based on classical molecular dynamics simulations of the atoms coupled to a classical dynamics of the spin system. We consider possible changes in the magnetization versus temperature, including variation of the Curie temperature and the critical exponent associated with the ferromagnetic-paramagnetic transition.In the case of the NPs we analyzed the effects of deformation twins on magnetic properties and found no significant difference between defective and ideal samples. For the bulk case we studied the effect of random vacancies and showed that the presence of vacancies lowers the Curie temperature and increases the critical exponent. These effects have their origin in the reduced exchanged interaction due to missing atoms. However, magnetic moments could increase near defects with reduced electronic density, like vacancies, and this effect was included in our simulation using a core-bulk model where different magnetic moments for atoms in the vicinity of the vacancies are considered. This leads to a compensation of the previous effect, and the Curie temperature increases, but does not reach the values for the ideal, non defective lattice