Evidence of local structural influence on the shape driven magnetic anisotropy in electronically excited Ni nanoparticles embedded in SiO2 matrix

Abstract

The reliance of modern electronic era on ultrafast data recording has made the search for novel tools to tune nano-scale magnetic-anisotropy (MA) never-ending. We demonstrate a strong correlation between the spin-spin interactions, local atomic structure and the MA of Ni nanoparticles (NPs) embedded inside SiO2 matrix under swift heavy ion (SHI) irradiation. In contrast to traditional understandings, MA in Ni NPs along with their aspect ratio, first increases upto 5 × 1013 ions/cm2 SHI fluence (5e13) and gets reduced at highest fluence. Using angle dependent Extented-Xray-Absorption-Fine-Structure (EXAFS) and ab initio molecular dynamics (MD) simulations, we show that the anisotropy induced in local atomic structure upon irradiation is dependent on atomic spin-spin interactions, which gets reduced at highest fluence. The chosen model cluster (Ni38) used in our MD simulations is duly validated by comparing the pair-correlation-function of the structure with the EXAFS-Fourier-Transform. The lattice temperatures for the films irradiated at different fluences, as calculated from thermal-spike-model, are used for the respective MD runs. We conclude that the enhanced disorder in both the local atomic environment and spin alignment destroys the MA at the highest fluence in SHI irradiated Ni NPs. The findings therefore provide rich conceptual insights for designing magnetic devices using SHI-induced phenomena.

Tuning LSPR of Thermal Spike-Induced Shape-Engineered Au Nanoparticles Embedded in Si3N4 Thin-Film Matrix for SERS Applications

“…This is what permits the LSPR to be detected. It is worth noting that this optical phenomenon is affected by a number of variables of dielectric NCs, including mean interparticle distances, particle morphology (size, shape, and distribution), and the dielectric function of the surrounding medium, , all of which can be engineered. Interestingly, it was determined that the SiO 2 matrix plays an intrinsic part in the process because free-standing Au NPs did not deform when irradiated with heavy ions of a high-energy range, popularly known as SHI.…”

“…SHI irradiation is a crucial method for altering the physical characteristics of materials and is frequently used to modify matter on the nanoscale. With amorphous-SiO 2 as the host matrix, one of the significant impacts of SHI exposure on a variety of metallic species, viz., Au, − Ag, , Co, Ni, − Zn, V, Pt, FePt, , FeCo, ,, and metal alloys, has been observed to be the elongation or ion-shaping of metal NPs. ,, Recent research has looked into the deformation strategy of spherical Au NPs ( diameters, ∼ca. 5–80 nm) implanted in SiO 2 when exposed to 50 MeV I 9+ SHI irradiation .…”

“…This eventually leads to the dissolution of NPs and surrounding insulating media, leading to the shape change of embedded NPs. Another mechanism is the “ion hammering effect”, which describes silicon oxide (silica) nanospheres’ deformation behavior and involves expanding in the ion beam’s direction while contracting in the opposite direction. , However, although theory and simulations ,, have proposed several mechanisms to explain the change of metallic NPs’ shape with ion track formation in an amorphous silica matrix, no conclusive theory has yet been developed. Some potential mechanisms that might be at play consist of NPs melting during a thermal spike, , changes in the volume extension or compaction of NPs and silica-based matrix causing creep deterioration carried on through an overpressure, ,, and in-plane strain at right angles to the path of the ion beam that causes shear stress-driven distortion .…”

“…Some potential mechanisms that might be at play consist of NPs melting during a thermal spike, , changes in the volume extension or compaction of NPs and silica-based matrix causing creep deterioration carried on through an overpressure, ,, and in-plane strain at right angles to the path of the ion beam that causes shear stress-driven distortion . Nonetheless, the shape anisotropy in the NPs is strongly correlated with their microstructural changes, viz., electronic and local structural modifications, and concurrently gives rise to several interesting macrostructural properties, viz., enhanced magnetic anisotropy, changes in optical properties, increase in field emission, , magnified SERS signals, etc.…”

Chemistry and interactions of silica based particles studied by liquid cell electron microscopy

“…In order to understand the underlying mechanism of silica elongation along the scanning direction, further experiments should be designed and compared with numerical simulation of the processes taking place. In the case of high energy (∼MeV), ion irradiation of silica particles with beams of charged ions such numerical investigations have already successfully performed [132,133]. For instance, using a randomly patterned electron beam where the scanning direction is not simply from left to right might result in a different type of shape deformation.…”