terahertz spectroscopy of electromagnons excitation in a hexaferrite ba 2 mg 2 fe 12 o 22
DESCRIPTION
Terahertz spectroscopy of electromagnons excitation in a hexaferrite Ba 2 Mg 2 Fe 12 O 22. Phy .Rev . B 80 , 220406(R) (2009). Phy.Rev.B 83 , 064422(2011). Ashida Lab. Tadataka Saito. Contents . Introduction Polarization and magnetization Multiferroics Electromagnon Method - PowerPoint PPT PresentationTRANSCRIPT
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Terahertz spectroscopy of electromagnons excitation in a hexaferrite Ba2Mg2Fe12O22
Ashida Lab.Tadataka Saito
Phy.Rev.B 83, 064422(2011)Phy.Rev. B 80, 220406(R) (2009)
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Contents
• Introduction Polarization and magnetization Multiferroics Electromagnon
• Method THzTDS
• Results • Conclusion
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Polarization and Magnetization
+ +
+ +
-
+ +
+ +
-
P-
-
Polarization
Magnetization
E
H M
Ferroelectric and Ferromagnetic
M=0
Application for memory devices
Introduction
分極 強誘電性と強磁性
磁化
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Multiferroics
E
H
P
M
Multiferroics are materials where ferroelectricity and ferromagnetism are inherently coupled.
The magnetization can be controlled by electric field of light.The polarization can be controlled by magnetic field.
Introduction
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Magnetoelectric effect(ME effect)
In 2003,RMnO3(R; rare earth element)
Polar lattice distortion Induce Polarization
Ptotal //c
Spiral-spin-order
)(, jiji SSeP
a
b
c
ji ,e
AntisymmetryDzyaloshinskii-Moriya interaction
iS jS
Introduction
空間格子の反転対称性の歪み
らせんスピン磁性
bc-spiral
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Electromagnon
Magnon can be excited by electric field of light.
Magnon
Introduction
Spin wave
Magnon is exited by magnetic field of light.
Multiferroics
Electromagnon (2006)
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Theory of electromagnonIntroduction
Ptotal //c
a
b
c
ji,e
iS jS)(, jiji SSeP
ij
jijis ttt )]()([)( , SSP
Eω//a
E
Mn
MnO
Symmetric exchange interaction
ME effect
iSjS
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Hexagonal ferrite Ba2Mg2Fe12O22
Ferri magnetic proper screw Conical spin
Room temperature T<195K T<50K
Introduction 六方晶フェライト
By neutron diffraction
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Transition of spin phase by magnetic field
H//[001]
Longitudinal conical spin
H(>3T)
0totalP
H//[100]
Transverse conical spin
H(> 4T)]120//[totalP
Introduction
FerrimagneticProper screw
Ferrimagnetic
0totalP 0totalP
θ
)](100//[)(
]001//[
)(
,
,,
transverseji
ji
jijijitotal
SS
e
SSeP
(001)
(100)(120)
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• THz-TDS enables us to observe a waveform of ”E(t)” directly.• By using THz-TDS , both amplitude and phase of ”E(t)” are
directly obtained.
Pump beam
Delay stage
Probe beam
THz-TDS
fs pulse laser
rE~ sE
~THz emitter
THz detector
sample
Terahertz time-domain spectroscopy (THz-TDS)
Method
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Longitudinal conical form
dSWTHz
THz1
4.0 00
Results
Conical
Proper-screw
Ferri
Conical Ferri
Proper
F
C
F
C
F
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Transverse conical form
dSWTHz
THz2.1
3.0 00
Results
Conical
ProperFerri
Proper-screwConical Ferri
F
C C
FF
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Conclusion ・ The electromagnon appears only in the conical spin ordered phase but irrespective of the longitudinal or the transverse conical form.No electromagnon is observed in the properscrew or ferrimagnetic phase.
・ The symmetric exchange interaction (Si ・ Sj) is dominant source of the observed electromagnon.
at room temperature
Electromagnon
Conclusion
Noncolinear spin structureat room temperature
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Purpose ・ To investigate the situation where electromagnon induced by changing temperature and external magnetic field
・ How the intensity of the absorption by electromagnon depend on the external magnetic field?
Is it possible to induce electromagnon at room temperature?
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Decide optical coefficient
dtetEE ti
)(
21)(~
))(exp()( E
d
Sample
inn )(~)(tEr )(tEs
Fourier transformed spectrum
1~2
n
tas1~~2
nntsa
saasrsr
s ttiEEt ))]()((exp[
)()()(~
Transmission Fresnel constants
2
1)()(ln)(
1)]arg()()([)(
saasr
s
saasrs
ttEE
dc
ttdcn
)()(2)(,)()()( 222
1 nn
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Experimental set up
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Emergency of electromagnondepend on the direction of electric field at conical spin phase(4.3K)
depend on the external magnetic field (H//[001],4.3K)
Phy.Rev. B 80, 220406(R) (2009)
Absorption by electromagnon is obserbed around 2.8meV(0.7THz).
Results
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Y-type
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Spiral spin structure
反時計回り
時計回り
反転対称性が崩れる格子歪みによる分極発生
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Electromagnon
………..H
MagnonEnergy
at THz region(0.1THz-10THz)0.41meV-41meV
・ observed at THz region・ depends on the direction of electric field・ The intensity of absorption depend on the external magnetic field.
[001]
[100]
[120]
L
S
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RMnO3 electromagnon