title: Magnetic Switching in Granular FePt Layers Promoted by Near-Field Laser Enhancement.
abstract: Light-matter interaction at the nanoscale in magnetic materials is a topic of intense research in view of potential applications in next-generation high-density magnetic recording. Laser-assisted switching provides a pathway for overcoming the material constraints of high-anisotropy and high-packing density media, though much about the dynamics of the switching process remains unexplored. We use ultrafast small-angle X-ray scattering at an X-ray free-electron laser to probe the magnetic switching dynamics of FePt nanoparticles embedded in a carbon matrix following excitation by an optical femtosecond laser pulse. We observe that the combination of laser excitation and applied static magnetic field, 1 order of magnitude smaller than the coercive field, can overcome the magnetic anisotropy barrier between "up" and "down" magnetization, enabling magnetization switching. This magnetic switching is found to be inhomogeneous throughout the material with some individual FePt nanoparticles neither switching nor demagnetizing. The origin of this behavior is identified as the near-field modification of the incident laser radiation around FePt nanoparticles. The fraction of not-switching nanoparticles is influenced by the heat flow between FePt and a heat-sink layer.
authors.affiliation: Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory , 2575 Sand Hill Road, Menlo Park, California 94025, United States.|van der Waals-Zeeman Institute, University of Amsterdam , 1018XE Amsterdam, The Netherlands.
authors.forename: Patrick W
authors.initials: PW
authors.lastname: Granitzka
authors.affiliation: Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory , 2575 Sand Hill Road, Menlo Park, California 94025, United States.
authors.forename: Emmanuelle
authors.identifier: 0000-0001-5297-9124
authors.initials: E
authors.lastname: Jal
authors.affiliation: Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory , 2575 Sand Hill Road, Menlo Park, California 94025, United States.|Spectroscopy and Coherent Scattering Instrument, European XFEL GmbH , Holzkoppel 4, 22869 Schenefeld, Germany.
authors.forename: Loïc
authors.initials: L
authors.lastname: Le Guyader
authors.affiliation: Institute for Quantum Electronics, Eidgenössische Technische Hochschule (ETH) Zürich , Auguste-Piccard-Hof 1, 8093 Zürich, Switzerland.
authors.forename: Matteo
authors.initials: M
authors.lastname: Savoini
authors.affiliation: Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory , 2575 Sand Hill Road, Menlo Park, California 94025, United States.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Higley
authors.affiliation: Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory , 2575 Sand Hill Road, Menlo Park, California 94025, United States.
authors.forename: Tianmin
authors.initials: T
authors.lastname: Liu
authors.affiliation: Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory , 2575 Sand Hill Road, Menlo Park, California 94025, United States.
authors.forename: Zhao
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory , 2575 Sand Hill Road, Menlo Park, California 94025, United States.
authors.forename: Tyler
authors.initials: T
authors.lastname: Chase
authors.forename: Hendrik
authors.initials: H
authors.lastname: Ohldag
authors.forename: Georgi L
authors.initials: GL
authors.lastname: Dakovski
authors.forename: William F
authors.initials: WF
authors.lastname: Schlotter
authors.forename: Sebastian
authors.initials: S
authors.lastname: Carron
authors.forename: Matthias C
authors.initials: MC
authors.lastname: Hoffman
authors.affiliation: Department of Physics, Temple University , 1925 N. 12th Street, Philadelphia, Pennsylvania 19122, United States.
authors.forename: Alexander X
authors.initials: AX
authors.lastname: Gray
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Padraic
authors.initials: P
authors.lastname: Shafer
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Elke
authors.initials: E
authors.lastname: Arenholz
authors.affiliation: San Jose Research Center, HGST a Western Digital Company, 3403 Yerba Buena Road, San Jose, California 95135, United States.
authors.forename: Olav
authors.initials: O
authors.lastname: Hellwig
authors.affiliation: San Jose Research Center, HGST a Western Digital Company, 3403 Yerba Buena Road, San Jose, California 95135, United States.
authors.forename: Virat
authors.initials: V
authors.lastname: Mehta
authors.affiliation: Magnetic Materials Unit, National Institute for Materials Science , Tsukuba 305-0047, Japan.
authors.forename: Yukiko K
authors.initials: YK
authors.lastname: Takahashi
authors.affiliation: Magnetic Materials Unit, National Institute for Materials Science , Tsukuba 305-0047, Japan.
authors.forename: Jian
authors.initials: J
authors.lastname: Wang
authors.affiliation: Center for Memory and Recording Research, University of California San Diego , 9500 Gilman Drive, La Jolla, California 92093-0401, United States.
authors.forename: Eric E
authors.initials: EE
authors.lastname: Fullerton
authors.affiliation: Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory , 2575 Sand Hill Road, Menlo Park, California 94025, United States.
authors.forename: Joachim
authors.initials: J
authors.lastname: Stöhr
authors.affiliation: Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory , 2575 Sand Hill Road, Menlo Park, California 94025, United States.
authors.forename: Alexander H
authors.initials: AH
authors.lastname: Reid
authors.affiliation: Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory , 2575 Sand Hill Road, Menlo Park, California 94025, United States.
authors.forename: Hermann A
authors.initials: HA
authors.lastname: Dürr
keywords: FePt; X-ray scattering; magnetic switching; pump−probe; ultrafast magnetism