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  • 1.
    Polley, Debanjan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Pancaldi, Matteo
    Hudl, Matthias
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Vavassori, Paolo
    Urazhdin, Sergei
    Bonetti, Stefano
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    THz-driven demagnetization with perpendicular magnetic anisotropy: towards ultrafast ballistic switching2018Ingår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, nr 8, artikel-id 084001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study THz-driven spin dynamics in thin CoPt films with perpendicular magnetic anisotropy. Femtosecond magneto-optical Kerr effect measurements show that demagnetization amplitude of about 1% can be achieved with a peak THz electric field of 300 kV cm(-1), and a corresponding peak magnetic field of 0.1 T. The effect is more than an order of magnitude larger than observed in samples with easy-plane anisotropy irradiated with the same field strength. We also utilize finite-element simulations to design a meta-material structure that can enhance the THz magnetic field by more than an order of magnitude, over an area of several tens of square micrometers. Magnetic fields exceeding 1 Tesla, generated in such meta-materials with the available laser-based THz sources, are expected to produce full magnetization reversal via ultrafast ballistic precession driven by the THz radiation. Our results demonstrate the possibility of table-top ultrafast magnetization reversal induced by THz radiation.

  • 2.
    Polley, Debanjan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zhou Hagström, Nanna
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. MBI Max-Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, Germany.
    von Korff Schmising, Clemens
    Eisebitt, Stefan
    Bonetti, Stefano
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Terahertz magnetic field enhancement in an asymmetric spiral metamaterial2018Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 51, nr 22, artikel-id 224001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We use finite element simulations in both the frequency and the time-domain to study the terahertz resonance characteristics of a metamaterial (MM) comprising a spiral connected to a straight arm. The MM acts as a RLC circuit whose resonance frequency can be precisely tuned by varying the characteristic geometrical parameters of the spiral: inner and outer radius, width and number of turns. We provide a simple analytical model that uses these geometrical parameters as input to give accurate estimates of the resonance frequency. Finite element simulations show that linearly polarized terahertz radiation efficiently couples to the MM thanks to the straight arm, inducing a current in the spiral, which in turn induces a resonant magnetic field enhancement at the center of the spiral. We observe a large (approximately 40 times) and uniform (over an area of similar to 10 mu m(2)) enhancement of the magnetic field for narrowband terahertz radiation with frequency matching the resonance frequency of the MM. When a broadband, single-cycle terahertz pulse propagates towards the MM, the peak magnetic field of the resulting band-passed waveform still maintains a six-fold enhancement compared to the peak impinging field. Using existing laser-based terahertz sources, our MM design allows to generate magnetic fields of the order of 2 T over a time scale of several picoseconds, enabling the investigation of nonlinear ultrafast spin dynamics in table-top experiments. Furthermore, our MM can be implemented to generate intense near-field narrowband, multi-cycle electromagnetic fields to study generic ultrafast resonant terahertz dynamics in condensed matter.

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