Spin-Lattice Dynamics Simulations: Magnetism under Compression and Hysteresis Loops of Samples with Defects

In this presentation, we report on recent findings obtained from spin-lattice dynamics simulations using the SPIN package of LAMMPS. The focus of our investigation lies on iron samples, including bulk, polycrystalline, and nanofoam structures, subjected to compression. During the elastic phase of compression, we observe an increase in magnetization, primarily attributed to a higher population of nearest-neighbor atoms and the resulting enhanced exchange interactions between spins. Conversely, in the plastic phase of compression, the presence of defects leads to a reduction in magnetization due to the creation of disorder and decreased atom coordination numbers. This effect is particularly pronounced in single crystals compared to polycrystals, where grain boundaries act as defects counteracting the magnetization increase during the elastic phase. Furthermore, we find that these effects are more pronounced at temperatures near the Curie temperature rather than at room temperature. Interestingly, in nanofoams, the effect of compression is minimal, as compression mainly occurs through void reduction and filament bending rather than strain within the ligaments. Additionally, we investigate the impact of defects on hysteresis loops in nanoparticles. Our results reveal that the inclusion of defects in spin-lattice dynamics simulations alters both the qualitative and quantitative behavior of the hysteresis loops in nanoparticles. The presence of defects leads to larger fluctuations and narrower hysteresis loops. Defective nanoparticles exhibit lower saturation magnetization and coercive field, resulting in a significantly reduced loop area compared to pristine nanoparticles. Overall, our findings shed light on the intricate relationship between magnetic properties and compression-induced structural changes as well as the effects of defects on hysteresis loops. This knowledge deepens our understanding of magnetism in diverse materials, providing valuable insights for the design and optimization of magnetic materials for various technological applications.