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Observation of magnetic domains in LSMO thin films by XMCD-PEEM

Fujimori Kiban-A Workshop 2005. Observation of magnetic domains in LSMO thin films by XMCD-PEEM. The Univ. of Tokyo A , Okayama Univ. B , JASRI C , AIST D , ISSP E , Tohoku Univ. F , NIMS G , KEK-PF H. M. Oshima A ,

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Observation of magnetic domains in LSMO thin films by XMCD-PEEM

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  1. Fujimori Kiban-A Workshop 2005 Observation of magnetic domains in LSMO thin films by XMCD-PEEM The Univ. of TokyoA, Okayama Univ.B, JASRIC, AISTD, ISSPE, Tohoku Univ.F, NIMSG, KEK-PFH M. OshimaA, T. TaniuchiA, H. KumigashiraA, H. YokoyaB, T. WakitaC, H. AkinagaD, M. LippmaaE, M. KawasakiF, H. KoinumaG and K. OnoH Contents １．Introduction ２．Objectives ３．Results and discussion PEEM observation of LSMO thin films ４．Summary 5. Research plans in the near future

  2. Photoelectron Emission Microscopy Phosphor e- hn 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 e- Specimen 1. Introduction PhotoElectron Emission Microscopy; PEEM EF 3d hn 2p PEEM by Oshima Group Features Spatial resolution: ~50 nm Projection imaging T. Taniuchi et al., JESRP114-117, 741 (2005)

  3. X-ray Magnetic Circular Dichroism (XMCD) (Right) (Left) L R hn hn s- s+

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

  5. La0.7Sr0.3MnO3 films Magnetic anisotropy of LSMO film strongly depends on substrate. LaAlO3 substrate NdGaO3 substrate SrTiO3 substrate *J. Dho et al., Appl. Phys. Lett. 82, 1434 (2003). La1-xSrxMnO3 / SrTiO3 →In-plane magnetic anisotropy In plane perpendicular MFM images(4 mm × 4 mm) Background of LSMO magnetic domains 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

  6. RHEED Monitoring Mask Pattern Moving Edge Ceramic Targets Pulsed Laser Deposition 2. Objectives of this study La1-xSrxMnO3 films Magnetic imaging SR-PEEM （PhotoElectron Emission Microscopy; PEEM） Laser MBE method Strained La0.8Sr0.2MnO3 (x = 0.2) / SrTiO3 Magnetic-structure observation La0.6Sr0.4MnO3 (x = 0.4)/ SrTiO3

  7. 3. Experimental: Preparation of La1-xSrxMnO3 films La0.6Sr0.4MnO3 (x = 0.4) La1-xSrxMnO3 films Laser MBE method Target La1-xSrxMnO3 sintered (x = 0.2 & 0.4) Substrate TC ~ 350 K Nb(0.05%)-SrTiO3(100) (TiO2-terminated) Terrace width: ~200 nm La0.8Sr0.2MnO3 (x = 0.2) Condition Annealed at 1050 ℃ @PO2 1.0×10-4 Torr thickness 100 ML(40 nm) Character -ization [in situ] RHEED, LEED [ex situ] AFM, XRD, ρ-T, SQUID 300 nm TC ~ 280 K K. Horiba et al., PRB 71, 155420 (2005).

  8. PEEM 120 cm 90 cm SR 30° Geometry 3. Experimental: PEEM system Magnetic imaging 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 ℃ XMCD-PEEM Measurement： SPring8 BL25SU KEK PF-AR BL-NE1B 　・Photon energy Mn L absorption edges 　　（620～680 eV） 　・resolution E/ΔE＞1000 PEEM system： PEEMSPECTOR (Elmitec) T. Taniuchi et al., JESRP114-117, 741 (2005)

  9. S. Imada et al. Physica B 281&282, 498 (2000). 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 nm 500 nm 20 mm PEEM image of stripe domains

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

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

  12. PEEM images of LSMO(x = 0.4) film Sample θ= 0° θ= 45° θ= 90° SR SR SR La0.67Sr0.33MnO3 film H θ *Z. H. Wang et al., Appl. Phys. Lett. 82, 3731 (2003).

  13. La0.67Sr0.33MnO3 film *Z. H. Wang et al., Appl. Phys. Lett. 82, 3731 (2003). Effective anisotropy constant per unit volume Film thickness Discussion: Origin of uniaxial magnetic anisotropy Uniaxial anisotropy of La1-xSrxMnO3 on SrTiO3 Magnetic anisotropy energy Uniaxial magnetic anisotropy Interfacial magnetic anisotropy Biaxial magnetic anisotropy ・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

  14. w 4π a2 4π (at + a2h/w) 4π at h Ka = Kc = Kb = a2 + at + (at + a2h/w) a2 + at + (at + a2h/w) a2 + at + (at + a2h/w) t a Uniaxial anisotropy in LSMO films Ka Kc Kb 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

  15. Uniaxial anisotropy in LSMO films [001] [100] [0-10] Previous works: easy axes in plane biaxial magnetic anisotropy → easy axes[100], [010] Uniaxial magnetic anisotropy in our study → Related with steps?

  16. 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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