Observation of magnetic domains in LSMO thin films by XMCD-PEEM M. Oshima A, T. Taniuchi A, H. Kumigashira A, H. Yokoya B, T. Wakita C, H. Akinaga D, M. Lippmaa E, M. Kawasaki F, H. Koinuma G and K. Ono H The Univ. of Tokyo A, Okayama Univ. B, JASRI C, AIST D, ISSP E, Tohoku Univ. F, NIMS G, KEK-PF H Contents １． Introduction ２． Objectives ３． Results and discussion PEEM observation of LSMO thin films ４． Summary 5. Research plans in the near future Fujimori Kiban-A Workshop 2005

PhotoElectron Emission Microscopy; PEEM Photoelectron Emission Microscopy Features Spatial resolution: ~50 nm Projection 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 2p2p 3d3d hnhn EFEF Phosphor e-e- e-e- Specimen hnhn PEEM by Oshima Group T. Taniuchi et al., JESRP , 741 (2005)

X-ray Magnetic Circular Dichroism (XMCD) (Right) (Left) h h  R L 

Magnetic Imaging by XMCD-PEEM SR K. Ono et al.,

Background of LSMO magnetic domains La 1-x Sr x MnO 3 / SrTiO 3 → In-plane magnetic anisotropy *J. Dho et al., Appl. Phys. Lett. 82, 1434 (2003). La 0.7 Sr 0.3 MnO 3 films SrTiO 3 substrate LaAlO 3 substrate NdGaO 3 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 ） RHEED Monitoring Pulsed Laser Deposition Moving Edge Mask Pattern Ceramic Targets Strained La 0.8 Sr 0.2 MnO 3 (x = 0.2) / SrTiO 3 La 0.6 Sr 0.4 MnO 3 (x = 0.4) / SrTiO 3 La 1-x Sr x MnO 3 filmsMagnetic imaging Magnetic-structure observation

3. Experimental: Preparation of La 1-x Sr x MnO 3 films La 0.8 Sr 0.2 MnO 3 (x = 0.2) La 0.6 Sr 0.4 MnO 3 (x = 0.4) 300 nm Target Substrate Character -ization Condition Nb(0.05%)-SrTiO 3 (100) (TiO 2 -terminated) Terrace width: ~200 nm Annealed at ×10 -4 Torr [in situ] RHEED, LEED [ex situ] AFM, XRD, ρ-T, SQUID thickness 100 ML (40 nm) Laser MBE method La 1-x Sr x MnO 3 films La 1-x Sr x MnO 3 sintered (x = 0.2 & 0.4) T C ~ 350 K T C ~ 280 K K. Horiba et al., PRB 71, (2005).

3. Experimental: PEEM system 120 cm 90 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 ＞ ° SR PEEM Geometry Magnetic imaging XMCD-PEEM T. Taniuchi et al., JESRP , 741 (2005)

20  m SR 4. Results and discussion: 1) PEEM images of LSMO(x = 0.4) film XMCD-PEEM in La 0.6 Sr 0.4 MnO 3 (x = 0.4) SR Sample Magnetic image (difference of acquired images) S. Imada et al. Physica B 281&282, 498 (2000). Photon energy: Mn L 3 edge (642 eV) Temperature: R.T. (~295 K) PEEM image of stripe domains SR 500 nm

PEEM images of LSMO(x = 0.4) film SR Sample SR θ= 0°θ= 45°θ= 90°

2) PEEM images of LSMO(x = 0.2) film SR Sample θ= 0° θ= 90° Lower than T C Higher than T C (T C = 280 K)

PEEM images of LSMO(x = 0.4) film SR Sample SR θ= 0°θ= 45°θ= 90° *Z. H. Wang et al., Appl. Phys. Lett. 82, 3731 (2003). La 0.67 Sr 0.33 MnO 3 film H θ

Discussion: Origin of uniaxial magnetic anisotropy Uniaxial anisotropy of La 1-x Sr x MnO 3 on SrTiO 3 *Z. H. Wang et al., Appl. Phys. Lett. 82, 3731 (2003). La 0.67 Sr 0.33 MnO 3 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 Magnetic anisotropy energy Effective anisotropy constant per unit volume Film thickness K u : 7.29x10 4 erg/cm 3 、 K eff 1 : 3.94x10 4 erg/cm 3

Uniaxial anisotropy in LSMO films w a t h Possibility of step-induced magnetic anisotropy → Comparison with metal films, SQUID measurements KbKb KaKa KcKc K a = a 2 + at + (at + a 2 h/w) 4π at K b = a 2 + at + (at + a 2 h/w) 4π (at + a 2 h/w) K c = a 2 + at + (at + a 2 h/w) 4π a 2 a = 5 mm, t = 40 nm, h = 0.39 nm & w = 100 nm → K c ~ 4π K a : K b : K c ~ 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