Terahertz radiation from coherent antiferromagnetic magnons excited by femtosecond laser pulses

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Terahertz radiation from coherent
antiferromagnetic magnons excited by femtosecond
laser pulses
APSE2010 Jun. 15, 2010 (Tue.)
?Junichi Nishitani, Takeshi Nagashima, Masanori
Hangyo Institute of Laser Engineering, Osaka
University
OSAKA Univ. Institute of Laser Engineering
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Terahertz wave
1 THz 1 ps 300 µm 33 cm-1 4.1 meV 48K

• Terahertz wave is the electromagnetic wave in the
  frequency region between microwave and infrared.
• The technologies in this THz region, ranging from
  0.1 THz to 10 THz, have made great progress
  recently with the invention of methods of
  generating and detecting THz radiation using
  ultrashort laser pulses.
• One of the most important applications of THz
  technology is the spectroscopy for characterizing
  various materials.

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• Terahertz emission spectroscopy

Observation of THz radiation from materials
Ultrafast dynamics of the microscopic properties

• Nonlinear optical effect
• Dynamics of photoexcited carriers
• Band structure

Recently, THz radiation emitted from
ferromagnetic material iron film has been
reported.
D. J. Hilton et al., J. Phys. Soc. Jpn. 75 (2006)

• THz emission spectroscopy is a potentially useful
  tool for

• Detection and manipulation of ultrafast electron
  spin dynamics in magnetic materials.
• Investigating ultrafast interaction between
  electron spin and optical pulse .

Development of ultrafast spintronics
In this study, we investigated THz radiation from
antiferromagnetic NiO excited by femtosecond
laser pulses.
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Antiferromagnetic(AFM) material NiO
One of the promising materials for spintronics
devices

• Rocksalt structure with inversion symmetry
• Spins are ferromagnetically ordered within 111
  planes.
• Ferromagnetic (111) layers are reversed in
  adjacent 111 planes.

• Magnetic easy-plane 111 planes

Single crystal NiO(110)
4mm
thickness 300 mm
10mm
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• Terahertz radiation from NiO

Radiation
Oscillations
Fourier transform
Coherent AFM magnons can be excited via impulsive
stimulated Raman scattering (ISRS) process.
Terahetz radiation from coherent
antiferromagnetic magnons
J. Nishitani et al., Appl. Phys. Lett. 96, 221906
(2010).
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Summary

• We have carried out THz emission spectroscopy on
  AFM NiO single crystals.
• The observed periodic oscillations in the
  waveforms are attributed to the radiation from
  coherent AFM magnons excited via ISRS process.
• THz emission spectroscopy on AFM materials is a
  useful technique for studying the fast response
  of their electron spins.