Transcript Folie 1

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Study of hexaferrite Ba0.6Sr1.4Zn2Fe12O22 by
EPR technique
Giorgi Khazaradze
Tbilisi, July10, 2014
What is Multiferroics?
Ferroelectric and Ferromagnetic orderings
Schematic picture of Multiferroic
Read
with
GMR
MF-RAM
Cycloidal spin ordering
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Multiferroic
Magnetoelectric effect
P=α H
M=α E
D. Khomshii, Physics 2, 20 (2009)
Write
with a
voltage
Pij=eij x (si x sj)
Dzyaloshinskii-Morya interaction
[M. Bibes and A. Barthélémy, Nat. Mater. 7, 425 (2008)]
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Type of hexaferrites
Schematic crystal structures of hexaferrites. The (110) cross section views of an M-type
(Ba,Sr)Fe12O19, W-type (Ba,Sr)Me2 Fe16O27, X-type (Ba,Sr)2 Me2Fe28 O46 , Y-type (Ba,Sr)2Me2
Fe12O22, Z-type (Ba,Sr)3Me2 Fe24 O41 , and U-type (Ba,Sr)4Me2Fe36O60 with the c axis vertical.
The (Fe,Me)-O-(Fe,Me) bond angles surrounded by dashed blue ellipsoids are strongly affected
by the ratio of Sr to Ba.
Kimura et al., Annu. Rev. Condens.Matter Phys. 2012. 3:93–110]
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a
b
c
d
a) cristal sructure, b-d magnetic structure of Y-type hehaferrite.
b) The proper-screw, c) the transverse-conical, d) the conical
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Kimura et al., Annu. Rev. Condens.Matter Phys. 2012. 3:93–110]
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Magnetic field dependence of electric polarization at different Temperatures and magnetic phase
diagram of High-T MF hexaferrite Ba0.5Sr1.5Zn2Fe12O22 with magnetic field perpendicular to
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the c axis
T. Kimura et al. Phys Rev. Lett. 94,137201 (2005)
Short description of EPR
•
•
•
Zeeman splitting by magnetic field.
9.6 GHz electromagnetic wave is
absorbed.
Linewidth of EPR is caused by the
interaction between the ions.
Ez=h𝝂=gµβH
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Ez −Zeeman energy
𝝂 − 𝑡ℎ𝑒 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑦 𝑜𝑓
the microwave field
Idea: apply electric field modulation and try to detect
magnetic resonance in ME materials
H=H‘+HmSin(2π𝝂mt)
H‘−𝑺𝒕𝒂𝒕𝒊𝒄 𝒂𝒑𝒑𝒍𝒊𝒆𝒅
𝒎𝒂𝒈𝒏𝒆𝒕𝒊𝒄 field
Hm−Modulation amplitude
𝝂m−Modulation frequency
𝝂m−100KHz
P(t)=PmSin(2π𝝂mt)
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P(t) –Detected absorbed
power
Schematic picture
of the experiment and the
Magnetic/Electric
field directions
A. Maisuradze Aet al., Phys. Rev. Lett., 108, 247211 (2012).
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Electric-field modulated FMR is selectively
sensitive to Magnetoelectric coupling in Cu2OSeO3
Temperature dependence of FMR signals of single-crystal Cu2OSeO3
detected using the MFM technique and the EFM technique
A. Maisuradze et al., Phys. Rev. Lett., 108, 247211 (2012).
Ferromagnetic resonance in Y-type
hexaferrite Ba0.6Sr1.4Zn2Fe12O22
0.3
FMR Signal, a.u.
Ba0.6Sr1.4Zn2Fe12O22
0.1
T=293K
0.0
-0.1
-0.2
-0.3
0
2000
4000
6000
Magnetic Field, G
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H
C axis
8000
Resonance field, G
7500
0.2
B
C
6000
Ba0.6Sr1.4Zn2Fe12O22
T=293K
4500
3000
1500
0
15
30
45
60
75
Angle , Degree
Angular dependence of
the resonance field
θ
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Ferromagnetic resonance in Y-type hexaferrite
Ba0.6Sr1.4Zn2Fe12O22 with Electric field modulation
0.25
Amplitude of firs FMR Line
Amplitude of firs FMR Line
100
T=293K
0
-100
-200
Ba0.6Sr1.4Zn2Fe12O22
T=273K
0.15
0.10
0.05
-300
2000
4000
6000
8000
Magnetic Field, G
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0.20
Ba0.6Sr1.4Zn2Fe12O22
Amplitude, a.u
FMR Signal, a.u.
200
FMR signal at Electric field
500
1000
1500
2000
2500
Electric field, V
The amplitude of FMR
signal as function
Electric field
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Magnetic and Electric Field Modulated FMR (EFMR) in
Ba0.6Sr1.4Zn2Fe12O22
0.6
Magnetic
Electric
0.2
FMR Signal, a.u.
FMR Signal, a.u.
0.4
Ba0.6Sr1.4Zn2Fe12O22
0.0
0
=60
T=293K
-0.2
Ba0.6Sr1.4Zn2Fe12O22
0.4
0
=90
T=293K
0.2
0.0
-0.2
-0.4
-0.4
0
2000
4000
6000
0
8000
Magnitoelectric coupling, 
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Magnetic Field, G
2000
4000
6000
Magnetic Field, G
8000
Coupling at second FMR line
Coupling at first FMR line
1E-6
Ba0.6Sr1.4Zn2Fe12O22
T=293K
T=293K
1E-7
1E-8
30
45
60
75
90
Angle , Degree
105
Angular dependence of the Magnetoelectric
(ME) coupling
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Summary and Conclusions
• Ferromagnetic resonance (FMR) in Y-type hexaferrite single
crystal Ba0.6Sr1.4Zn2Fe12O22 was observed.
• Using electric field modulation FMR (EFMR) technique
magnetoelectric coupling was observed in this compound.
•
Magnetoelectric coupling was estimated, however it is week at
room temperature.
• Magnetoelectric coupling was determined quantitatively as a
function of temperature and magnetic field orientation.
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Outlook
• The next step would be to study this compound at lower
temperatures and appropriate magnetic field range where
electric polarization was observed by using Soft X-ray Scattering
method.
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Thanks for your
Attention!
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