Triggering of spin-flipping-modulated exchange bias in FeCo nanoparticles by electronic excitation

Abstract

The exchange coupling between ferromagnetic (FM)-antiferromagnetic (AF) interfaces is a key element of modern spintronic devices. We here introduce a new way of triggering exchange bias (EB) in swift heavy ion (SHI) irradiated FeCo-SiO2 films, which is a manifestation of spin-flipping at high irradiation fluence. The elongation of FeCo nanoparticles (NPs) in SiO2 matrix gives rise to perpendicular magnetic anisotropy at intermediate fluence. However, a clear shift in hysteresis loop is evident at the highest fluence. This reveals the existence of an AF exchange pinning domain in the NPs, which is identified not to be oxide shell from XANES analysis. Thermal spike calculations along with first-principles based simulations under the framework of density functional theory (DFT) demonstrate that spin flipping of 3d valence electrons is responsible for formation of these AF domains inside the FM NPs. EXAFS experiments at Fe and Co K-edges further unravel that spin-flipping in highest fluence irradiated film results in reduced bond lengths. The results highlight the possibility of miniaturization of magnetic storage devices by using irradiated NPs instead of conventionally used FM-AF multilayers.

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

“…As a result of these local structural modifications, we have observed (i) triggering of the spin-flipping modulated exchange bias effect at high irradiation dose in FeCo NPs, (ii) reduction in Fe-Co nearest-neighbour distances (i.e. 1 st shell Fe-Co bond lengths) 27 . In Ni NPs, the spin-spin interaction affects the second nearest neighbour co-ordination 26 and hence a local structural anisotropy is generated in post-irradiated NPs.…”

“…FeCo 23 , 24 or Ni 25 , 26 differently. The spin-spin interaction controls the local structural parameters in these ferromagnetic nanoclusters 26 , 27 . As a result of these local structural modifications, we have observed (i) triggering of the spin-flipping modulated exchange bias effect at high irradiation dose in FeCo NPs, (ii) reduction in Fe-Co nearest-neighbour distances (i.e.…”

Plasmonic Nanoparticles in Dielectrics Synthesized by Ion Beams: Optical Properties and Photonic Applications

“…[ 74 ] As shown in Figure , the elongated embedded NPs are perfectly aligned along the controllable beam direction and well protected by the dielectrics, which overcomes the limitation of unstability and weak anisotropy by integrated effects of randomly arranged NPs. [ 74 ] To date, there are two major mechanisms proposed for the elongation: a) synergy effects by ion hammering and NP melting, [ 75–82 ] and b) ion shaping by ion tracks. [ 83–88 ] Ion hammering was discovered by Klaumunzer in 1983 that the NP dimensions grow (shrink) perpendicular (parallel) to the ion beam direction, which has been well understood by effective‐flow temperature approach.…”

Tuning the Magnetic Properties of FeCo Thin Films through the Magnetoelastic Effect Induced by the Au Underlayer Thickness

“…Our ab initio calculations were based on spin-polarized DFT within the formulation proposed by Perdew–Burke–Ernzerhof (PBE) for the exchange–correlation energy functional, which provide an accurate description of the physical properties addressed in this work such as alloys, lattice parameters, magnetic anisotropy energies, and so forth. ,− The Kohn–Sham equations were solved using the all-electron projected augmented-wave method, , as implemented in the widely used Vienna Ab initio Simulation Package (VASP), version 5.4.4. , The equilibrium geometries for all calculations were obtained using the scalar-relativistic approximation to describe the valence electrons, that is, spin–orbit coupling (SOC) was not taken into account for the valence states, however, the SOC within the non-collinear spin approach was considered to calculate the magnetic properties . For all calculations, we employed a self-consistent electronic convergence criteria of 10 –6 eV, while the optimized structures were obtained once the atomic forces are smaller than 0.010 eV Å –1 on all atoms.…”