title: 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-SiO2films, which is a manifestation of spin-flipping at high irradiation fluence. The elongation of FeCo nanoparticles (NPs) in SiO2matrix 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.
authors.affiliation: Department of Physics, Indian Institute of Technology Delhi, Hauz Khas 110016, New Delhi, India.
authors.forename: Debalaya
authors.initials: D
authors.lastname: Sarker
authors.affiliation: Department of Physics, Indian Institute of Technology Delhi, Hauz Khas 110016, New Delhi, India.
authors.forename: Saswata
authors.initials: S
authors.lastname: Bhattacharya
authors.affiliation: Department of Physics, Indian Institute of Technology Delhi, Hauz Khas 110016, New Delhi, India.
authors.forename: Pankaj
authors.initials: P
authors.lastname: Srivastava
authors.affiliation: Department of Physics, Indian Institute of Technology Delhi, Hauz Khas 110016, New Delhi, India.
authors.forename: Santanu
authors.initials: S
authors.lastname: Ghosh