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Proceedings Paper

Terahertz time-domain spectroscopy of magnons in antiferromagnetic MnF2 (Conference Presentation)
Author(s): Alan D. Bristow; Derek A. Bas; Pavel Borisov; David Lederman

Paper Abstract

Antiferromagnets are an important class of ordered spin systems, common in spintronic applications and providing a testbed for studying magnetism. Recently, the injection of magnons – coherent spin waves – has been explored by broadband terahertz pulses in antoferromagnets, such as MnO. Here, terahertz time-domain spectroscopy is used to detect magnon resonances in MnF2, which is a model antiferromagnet with uniaxial anisotropy and a Néel temperature of 67 K. Temperature dependence of a one-magnon resonances is examined from 5 K to 70 K. The center frequency of the one-magnon is recorded below the Néel temperature and fit to a Brillouin function. It is found that the degree of correlation between neighboring spins is j = 1.1. Namely, a weak correlation and appropriately modeled by mean-field theory befitting this simple system. From low temperature to room temperature, a two-magnon resonance is observed to broaden and strengthen as the temperature increases. Two-magnon modes arise due to zone-edge magnons being stimulated with -k and +k momenta and do not require magnetic ordering. Over this same temperature range, THz transients are used to monitor the time-of flight through the crystal, the refractive index, the internal energy and the heat capacity. Overall these quantities decrease with decreasing temperature, with behavior that falls into three regimes: a thermal dominated region above the Néel temperature, a magnetic regime below the Néel temperature; and a hyperfine interaction region at temperatures below 6 K. The latter is the first direct observation of the hyperfine interaction using terahertz time-domain spectroscopy.

Paper Details

Date Published: 19 April 2017
PDF: 1 pages
Proc. SPIE 10102, Ultrafast Phenomena and Nanophotonics XXI, 101020V (19 April 2017); doi: 10.1117/12.2250627
Show Author Affiliations
Alan D. Bristow, West Virginia Univ. (United States)
Derek A. Bas, West Virginia Univ. (United States)
Pavel Borisov, West Virginia Univ. (United States)
David Lederman, West Virginia Univ. (United States)
Univ. of California, Santa Cruz (United States)

Published in SPIE Proceedings Vol. 10102:
Ultrafast Phenomena and Nanophotonics XXI
Markus Betz; Abdulhakem Y. Elezzabi, Editor(s)

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