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Sustained coherent spin wave emission using frequency combs

Journal article
Authors Shreyas Muralidhar
Ahmad Awad
Ademir F. Alemán Hernández
Roman Khymyn
Mykola Dvornik
Dag Hanstorp
Johan Åkerman
Published in Physical Review B
Volume 101
Issue 22
ISSN 2469-9950
Publication year 2020
Published at Department of Physics (GU)
Language en
Links dx.doi.org/10.1103/PhysRevB.101.224...
Keywords excitation, Materials Science, Physics
Subject categories Physical Sciences

Abstract

We demonstrate sustained coherent emission of spin waves in NiFe films using rapid demagnetization from high repetition rate femtosecond laser pulse trains. As the pulse separation is shorter than the magnon decay time, magnons having a frequency equal to a multiple of the 1 GHz repetition rate are coherently amplified. Using scanning Brillouin light scattering (BLS) microscopy, we observe this coherent amplification as strong peaks spaced 1 GHz apart. The BLS counts vs laser power exhibit a stronger than parabolic dependence consistent with counts being proportional to the square of the magnetodynamic amplitude, and the demagnetization pulse strength being described by a Bloch law. Spatial spin wave mapping demonstrates how both localized and propagating spin waves can be excited, and how the propagation direction can be directly controlled. Our results demonstrate the versatility of frequency combs and BLS spectroscopy for rapid demagnetization studies, and enable a platform for photomagnonics where sustained coherent spin waves can be utilized.

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