Terahertz time-domain spectroscopy of magnons in antiferromagnetic MnF2 (Conference Presentation)

Alan D. Bristow; Derek A. Bas; Pavel Borisov; David Lederman

doi:10.1117/12.2250627

19 April 2017 Terahertz time-domain spectroscopy of magnons in antiferromagnetic MnF₂(Conference Presentation)

Alan D. Bristow, Derek A. Bas, Pavel Borisov, David Lederman

Proceedings Volume 10102, Ultrafast Phenomena and Nanophotonics XXI; 101020V (2017) https://doi.org/10.1117/12.2250627
Event: SPIE OPTO, 2017, San Francisco, California, United States

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.

Conference Presentation

Citation Download Citation

Alan D. Bristow, Derek A. Bas, Pavel Borisov, and David Lederman "Terahertz time-domain spectroscopy of magnons in antiferromagnetic MnF₂(Conference Presentation)", Proc. SPIE 10102, Ultrafast Phenomena and Nanophotonics XXI, 101020V (19 April 2017); https://doi.org/10.1117/12.2250627

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KEYWORDS

Terahertz spectroscopy

Magnons

Spectroscopy

Magnetism

Anisotropy

Crystals

Spintronics

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