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

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)

X-ray Magnetic Circular Dichroism (XMCD)

(Right)(Left)

h h

R L

Magnetic Imaging by XMCD-PEEM

SRK. Ono et al.,

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

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

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).

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)

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

PEEM images of LSMO(x = 0.4) film

SR

Sample

SR

SR

θ= 0° θ= 45° θ= 90°

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)

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

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

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

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?

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