Complex Epitaxial Oxides: Synthesis and Scanning Probe Microscopy Goutam Sheet, 1 Udai Raj Singh, 2 Anjan K. Gupta, 2 Ho Won Jang, 3 Chang-Beom Eom 3 and Venkat Chandrasekhar 1 1 Department of Physics and Astronomy, Northwestern University, Evanston, IL,USA 2 Dept. Of Physics, Indian Institute of Technology, Kanpur, India 3 Dept. Of Materials Science and Engineering, University of Wisconsin-Madison, Wisconsin, USA SEM images of (a) LSMO and (b) CFO nano-pillar arrays STO SROCFO Ferroelectric/Piezoelectric (1) (2) (3) (5) (6) STO (4) Multiferroic heterostructures: Fabrication & Characterization (a) Topography and (b) MFM images of CFO nano-pillar arrays (MFM lift height = 30 nm) No clear contrast is observed at the top of a single nano- pillar, which indicates that each pillar is a single-domain magnet. Most possibly, the magnetization in the pillar is completely out-of-plane. However, the possibility of a canted magnetization cannot be ruled out from these data. We have performed room temperature magnetic force microscopy (MFM) on CFO nano-pillars to study their magnetic domain structures and anisotropy. At room temperature, CFO is a ferromagnetic oxide which shows 45 0 out-of-plane magnetization in thin films. On as-grown samples On the samples annealed at C in air Figure 3: Topography of as-grwon film at 78 K. The surface is granular due to a fast growth rate. Figure 4: STS spectra on as-grown film at three different temperatures. There is not much temperature evolution. Figure 5: Topography (left) and conductance (right) image of the annealed film at 78 K. The variation in the conductance is less than 5 %. We may not see the inhomogeneities in the STM-S data as the STM technique is very surface sensitive On as-grown samples After annealing at C in air Topography of as-grown film at 78 K. Scan range is 205 nm x 205 nm The surface is granular Figure 4: STS spectra on as-grown film at three different temperatures. The spectra do not show a strong temperature dependence Topography of the annealed film at 295 K. Scale: 500x500 nm 2 The line profile corresponding to the green line on the topography image is shown. The terraces are formed with single unit cell height (~ 0.4 nm). Terraces are formed during post-growth annealing and we do not see regular step-terrace morphology, most likely due to the substrate on which these films are grown. (a) STS spectra on the annealed film at different temperatures. (b) Representative I-V curves All the spectra at different temperatures were captured at the same tunneling resistance (bias voltage = 1 V and current = 0.1 nA). Topography (left) and conductance (right) image of the annealed film at 78 K. Scan range is 524 nm x 524 nm. The variation in the conductance is less than 5 %. Inhomogeneities in the bulk are not probed as STM is very surface sensitive Scanning Tunneling Microscopy and Spectroscopy on La 0.7 Sr 0.3 MnO 3 : Evidence for a Pseudogap The spectra below 150 K are more gap-like: A pseudogap in the metallic state!! The pseudogap observed in the metallic state might be the signature of localized polarons arising from the strong coupling between electrons and dynamic Jahn-Teller distortions while a finite DOS at the Fermi energy indicates presence of the delocalized carriers in the metallic state. The pseudogap could also originate from the dynamic phase separation as suggested by recent Monte Carlo simulations. Perovskite oxides exhibit exotic physical properties like ferroelectricity, ferromagnetism, and superconductivity. Heterostructures of more than one such oxide with different physical properties may be tailored leading to multifunctional properties. We have synthesized nanometer scale heterostructures of ferroelectrics and ferromagnets, and ferromagnets and superconductors to study fundamental physics including the interplay of multiple physical phenomena. We employ scanning probe techniques including atomic force microscopy (AFM), magnetic force microscopy (MFM), electrostatic force microscopy (EFM) and scanning tunneling microscopy (STM) at varying temperatures and magnetic fields to study such phenomena. Here we report on two issues related to our research: fabrication of multiferroic heterostructures and their characterization using magnetic force microscopy, and observation of a pseudogap in the metallic state of the broad bandwidth manganite La 0.7 Sr 0.3 MnO 3 using scanning tunneling microscopy and spectroscopy. Ongoing research and future goals: 1.Imaging the intrinsic inhomogeneities in manganites and studying their temperature and magnetic field dependence using our homebuilt variable temperature EFM and MFM. 2. Probing the Andreev bound states between d-wave superconductors and ferromagnets as a function of temperature, magnetic field and the spin polarization of the ferromagnet using our variable temperature STM. 3.Controlling the magnetization axis of the nanostructured ferromagnetic pillars in a ferroelectric matrix by electric field. 1.The substrate (STO [001]) 2.Deposition of CFO or LSMO with a SRO underlayer 3.e-beam patterning ion milling 5.Deposition of the matrix layer 6.Planarization by low angle ion milling Blown up image showing the single domain structures References: 1. E. Dagotto et. al., Phys. Rep. 344, 1 (2001). 2. A. Chikamatsu et. al., Phys. Rev. B 76, (2007). 3. Yu. et. al., Phys. Rev. B 77, (2008). 4. Mannella et. al., Nature 438, 474 (2005). Magnetization and transport measurements on a LSMO thin film (a) (b)