Observation of magnetic domains in LSMO thin films by XMCD-PEEM
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Observation of magnetic domains in LSMO thin films by XMCD-PEEM
M. OshimaA, T. TaniuchiA, H. KumigashiraA, H. YokoyaB, T. WakitaC, H. A
kinagaD, M. LippmaaE, M. KawasakiF, H. KoinumaG and K. OnoH
The Univ. of TokyoA, Okayama Univ.B, JASRIC, AISTD, ISSPE,
Tohoku Univ.F, NIMSG, KEK-PFH
Contents1. Introduction2. Objectives3. Results and discussion
PEEM observation of LSMO thin films4. Summary5. Research plans in the near future
Fujimori Kiban-A Workshop 2005
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PhotoElectron Emission Microscopy; PEEM
Photoelectron Emission Microscopy
FeaturesSpatial resolution: ~50 nmProjection imaging
Features of SR-PEEM・ Element selective contrast・ Real-space mapping of magnetization・ Direct observation of antiferromagnetic domain (linear polarized light)・ Micro-spectroscopy (μ-XAS, μ-EXAFS)・ Time resolved imaging
1. Introduction
2p
3d
h
EF
Phosphor
e-
e-
Specimen
h
PEEM by Oshima Group
T. Taniuchi et al., JESRP114-117, 741 (2005)
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X-ray Magnetic Circular Dichroism (XMCD)
(Right)(Left)
h h
R L
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Magnetic Imaging by XMCD-PEEM
SRK. Ono et al.,
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Background of LSMO magnetic domains
La1-xSrxMnO3 / SrTiO3
→ In-plane magnetic anisotropy
*J. Dho et al., Appl. Phys. Lett. 82, 1434 (2003).
La0.7Sr0.3MnO3 filmsSrTiO3
substrateLaAlO3
substrateNdGaO3
substrate
MFM images(4 m × 4 m)
Magnetic anisotropy of LSMO film strongly depends on substrate.
perpendicular In plane
Furthermore…In the case that substrate has a step and terrace structure.
・ Crystal asymmetry at the surface・ Change in symmetry due to step structure・ Commensurate lattice constant at interface・ Lower coordination than bulk
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2. Objectives of this study
Laser MBE method
SR-PEEM( PhotoElectron Emission
Microscopy; PEEM )RHEEDMonitoring
Pulsed LaserDeposition
Moving EdgeMask Pattern
Ceramic Targets
StrainedLa0.8Sr0.2MnO3 (x = 0.2) / SrTiO3
La0.6Sr0.4MnO3 (x = 0.4) / SrTiO3
La1-xSrxMnO3 films Magnetic imaging
Magnetic-structure observation
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3. Experimental: Preparation of La1-xSrxMnO3 films
La0.8Sr0.2MnO3 (x = 0.2)
La0.6Sr0.4MnO3 (x = 0.4)
300 nm
Target
Substrate
Character-ization
Condition
Nb(0.05%)-SrTiO3(100)(TiO2-terminated)Terrace width: ~200 nm
Annealed at 1050 ℃@PO2 1.0×10-4 Torr
[in situ] RHEED, LEED[ex situ] AFM, XRD, ρ-T, SQUID
thickness 100 ML (40 nm)
Laser MBE method
La1-xSrxMnO3 films
La1-xSrxMnO3 sintered(x = 0.2 & 0.4)
TC ~ 350 K
TC ~ 280 K
K. Horiba et al., PRB 71, 155420 (2005).
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3. Experimental: PEEM system
120 cm90 cm
PEEM system :PEEMSPECTOR (Elmitec)
PEEM system ・ Spatial resolution : ~ 35 nm (Hg lamp) ・ Manipulation x y z translation, x y tilting and azimuthal rotaion ・ Vibration damping Air damper and pumping by ion pump ・ Temperature –120 ~ 400 ℃
Measurement : SPring8 BL25SU KEK PF-AR BL-NE1B ・ Photon energy Mn L absorption edges ( 620 ~ 680 eV ) ・ resolution E/ΔE > 1000
30°
SR
PEEM
Geometry
Magnetic imaging
XMCD-PEEM
T. Taniuchi et al., JESRP114-117, 741 (2005)
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20 m
SR
4. Results and discussion: 1) PEEM images of LSMO(x = 0.4) film
XMCD-PEEMin La0.6Sr0.4MnO3 (x = 0.4)
SR
Sample
Magnetic image (difference of acquired images)
S. Imada et al. Physica B 281&282, 498 (2000).
Photon energy: Mn L3edge (642 eV)
Temperature: R.T. (~295 K)
PEEM image of stripe domains
SR
500 nm500 nm
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PEEM images of LSMO(x = 0.4) film
SR
Sample
SR
SR
θ= 0° θ= 45° θ= 90°
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2) PEEM images of LSMO(x = 0.2) film
SR
SR
Sample
θ= 0°
θ= 90°
Lower than TC Higher than TC
(TC = 280 K)
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PEEM images of LSMO(x = 0.4) film
SRSR
Sample
SR
θ= 0° θ= 45° θ= 90°
*Z. H. Wang et al., Appl. Phys. Lett. 82, 3731 (2003).
La0.67Sr0.33MnO3 film
Hθ
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Discussion: Origin of uniaxial magnetic anisotropy
Uniaxial anisotropy of La1-xSrxMnO3 on SrTiO3
*Z. H. Wang et al., Appl. Phys. Lett. 82, 3731 (2003).
La0.67Sr0.33MnO3 film
・ Crystal asymmetry at the interface・ Change in symmetry due to step structure・ Commensurate lattice constant at the interface
Uniaxial magnetic anisotropy
Biaxial magnetic
anisotropy
Interfacial magnetic
anisotropy
S22eff
12
eff )4
∂(cos)
4
∂(cossin KtKtKtK u +−+⋅⋅+⋅⋅=⋅ θθθ
Magnetic anisotropy energy
:effK:t
Effective anisotropy constant per unit volume
Film thickness
Ku: 7.29x104 erg/cm3 、 Keff1: 3.94x104 erg/cm3
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Uniaxial anisotropy in LSMO films
w
a
t
h
Possibility of step-induced magnetic anisotropy
→ Comparison with metal films, SQUID measurements
Kb
Ka
Kc
Ka = a2 + at + (at + a2h/w) 4π at
Kb = a2 + at + (at + a2h/w)4π (at + a2h/w)
Kc = a2 + at + (at + a2h/w) 4π a2
a = 5 mm, t = 40 nm, h = 0.39 nm & w = 100 nm
→ Kc ~ 4π Ka : Kb : Kc ~ 1 : 500 : 1,200,000
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Uniaxial anisotropy in LSMO films
[0-10] [100]
[001]
Previous works: easy axes in plane biaxial magnetic anisotropy → easy axes[100], [010]
Uniaxial magnetic anisotropy in our study
→ Related with steps?
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4 . Summary
Growth of LSMO/STO stepped substrates=>Electrical and magnetic properties identical to bulk crystals
Observation of magnetic domains in LSMO/STO ・ 1. LSMO (x=0.4): Magnetic domain structures along the substrate steps with several microns
2. LSMO (x=0.2): Magnetic domains observed at low temperature disappeared at RT.
→ New possibility of controlling magnetic domain structures by means of step structures