Fujimori Kiban-A Workshop 2005 Observation of magnetic domains in LSMO thin films by XMCD-PEEM M. OshimaA, T. TaniuchiA, H. KumigashiraA, H. YokoyaB, T. WakitaC, H. AkinagaD, 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 Contents １．Introduction ２．Objectives ３．Results and discussion PEEM observation of LSMO thin films ４．Summary 5. Research plans in the near future 1. Introduction Photoelectron Emission Microscopy PhotoElectron Emission Microscopy; PEEM Phosphor EF 3d hn 2p e- hn Features of SR-PEEM eSpecimen ・Element selective contrast ・Real-space mapping of magnetization PEEM by Oshima Group・Direct observation of antiferromagnetic domain (linear polarized light) ・Micro-spectroscopy (μ-XAS, μ-EXAFS) ・Time resolved imaging Features Spatial resolution: ~50 nm Projection imaging T. Taniuchi et al., JESRP114-117, 741 (2005) X-ray Magnetic Circular Dichroism (XMCD) (Right) hn R s+ (Left) L hn s- Magnetic Imaging by XMCD-PEEM SR K. Ono et al., Background of LSMO magnetic domains La0.7Sr0.3MnO3 films LaAlO3 NdGaO3 SrTiO3 substrate substrate substrate Magnetic anisotropy of LSMO film strongly depends on substrate. *J. Dho et al., Appl. Phys. Lett. 82, 1434 (2003). La1-xSrxMnO3 / SrTiO3 → In-plane magnetic anisotropy perpendicular In plane MFM images(4 mm × 4 mm) Furthermore… ・Crystal asymmetry at the surface In the case that substrate has a step ・Change in symmetry due to step structure and terrace structure. ・Commensurate lattice constant at interface ・ Lower coordination than bulk 2. Objectives of this study La1-xSrxMnO3 films Laser MBE method RHEED Monitoring Moving Edge Ceramic Targets Magnetic imaging SR-PEEM （PhotoElectron Emission Microscopy; PEEM） Mask Pattern Pulsed Laser Deposition Strained La0.8Sr0.2MnO3 (x = 0.2) / SrTiO3 La0.6Sr0.4MnO3 (x = 0.4) / SrTiO3 Magnetic-structure observation 3. Experimental: Preparation of La1-xSrxMnO3 films La1-xSrxMnO3 films La0.6Sr0.4MnO3 (x = 0.4) Laser MBE method Target Substrate La1-xSrxMnO3 sintered (x = 0.2 & 0.4) Nb(0.05%)-SrTiO3(100) (TiO2-terminated) Terrace width: ~200 nm TC ~ 350 K La0.8Sr0.2MnO3 (x = 0.2) Condition Annealed at 1050 ℃ @PO2 1.0×10-4 Torr thickness 100 ML (40 nm) Character [in situ] -ization RHEED, LEED [ex situ] AFM, XRD, ρ-T, SQUID 300 nm TC ~ 280 K K. Horiba et al., PRB 71, 155420 (2005). 3. Experimental: PEEM system Magnetic imaging XMCD-PEEM 90 cm 120 cm PEEM system： PEEMSPECTOR (Elmitec) T. Taniuchi et al., JESRP114-117, 741 (2005) 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 SR （620～680 eV） ・resolution 30° E/ΔE＞1000 PEEM Geometry 4. Results and discussion: 1) PEEM images of LSMO(x = 0.4) film XMCD-PEEM in La0.6Sr0.4MnO3 (x = 0.4) Magnetic image (difference of acquired images) SR Photon energy: Mn L3edge (642 eV) SR Temperature: R.T. (~295 K) SR Sample 500 500nm nm 20 mm S. Imada et al. Physica B 281&282, 498 (2000). PEEM image of stripe domains PEEM images of LSMO(x = 0.4) film θ= 0° Sample θ= 45° θ= 90° SR SR SR 2) PEEM images of LSMO(x = 0.2) film Lower than TC θ= 0° Higher than TC Sample SR θ= 90° SR (TC = 280 K) PEEM images of LSMO(x = 0.4) film θ= 0° Sample θ= 45° θ= 90° SR SR SR La0.67Sr0.33MnO3 film θ H *Z. H. Wang et al., Appl. Phys. Lett. 82, 3731 (2003). Discussion: Origin of uniaxial magnetic anisotropy Uniaxial anisotropy of La1-xSrxMnO3 on SrTiO3 Magnetic anisotropy energy π π K eff t K u t sin 2 + K1eff t cos 2 ( + ) cos 2 ( - ) + KS 4 4 Uniaxial magnetic anisotropy Interfacial Biaxial magnetic magnetic anisotropy anisotropy Keff : Effective anisotropy constant per unit volume t: Film thickness La0.67Sr0.33MnO3 film ・Crystal asymmetry at the interface ・Change in symmetry due to step structure ・Commensurate lattice constant at the interface Ku: 7.29x104 erg/cm3、Keff1: 3.94x104 erg/cm3 *Z. H. Wang et al., Appl. Phys. Lett. 82, 3731 (2003). Uniaxial anisotropy in LSMO films w Ka h Kc t Kb a 4π at 4π (at + a2h/w) 4π a2 Ka = a2 + at + (at + a2h/w) Kb = a2 + at + (at + a2h/w) Kc = a2 + at + (at + a2h/w) a = 5 mm, t = 40 nm, h = 0.39 nm & w = 100 nm → Kc ~ 4π Ka : Kb : Kc ~ 1 : 500 : 1,200,000 Possibility of step-induced magnetic anisotropy → Comparison with metal films, SQUID measurements Uniaxial anisotropy in LSMO films Previous works: easy axes in plane biaxial magnetic anisotropy → easy axes[100], [010] [001] [0-10] Uniaxial magnetic anisotropy in our study → Related with steps? [100] 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
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