THz-Driven Ultrafast Spin-Lattice Scattering in Amorphous Metallic Ferromagnets

S. Bonetti, M. C. Hoffmann, M.-J. Sher, Z. Chen, S.-H. Yang, M. G. Samant, S. S. P. Parkin, and H. A. Dürr

Phys. Rev. Lett. 117, 087205 – Published 17 August 2016

Abstract

We use single-cycle THz fields and the femtosecond magneto-optical Kerr effect to, respectively, excite and probe the magnetization dynamics in two thin-film ferromagnets with different lattice structures: crystalline Fe and amorphous CoFeB. We observe Landau-Lifshitz-torque magnetization dynamics of comparable magnitude in both systems, but only the amorphous sample shows ultrafast demagnetization caused by the spin-lattice depolarization of the THz-induced ultrafast spin current. Quantitative modeling shows that such spin-lattice scattering events occur on similar time scales than the conventional spin conserving electronic scattering ( $\sim 30 fs$ ). This is significantly faster than optical laser-induced demagnetization. THz conductivity measurements point towards the influence of lattice disorder in amorphous CoFeB as the driving force for enhanced spin-lattice scattering.

Received 15 April 2016

DOI:https://doi.org/10.1103/PhysRevLett.117.087205

Physics Subject Headings (PhySH)

Magneto-optical Kerr effect Ultrafast phenomena

Ferromagnets

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

S. Bonetti^1,*, M. C. Hoffmann², M.-J. Sher^3,4, Z. Chen^3,5, S.-H. Yang⁶, M. G. Samant⁶, S. S. P. Parkin^6,7, and H. A. Dürr^3,†

¹Department of Physics, Stockholm University, Stockholm 10691, Sweden
²Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
³Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
⁴Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, USA
⁵Department of Physics, Stanford University, Stanford, California 94305, USA
⁶IBM Almaden Research Center, San Jose, California 95120, USA
⁷Max-Planck Institut für Mikrostrukturphysik, Weinberg 2, Halle 06120, Germany