Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session B24: Focus Session: Dielectric, Ferroelectric, and Piezoelectric Oxides -- Thin Film Multiferroics |
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Sponsoring Units: DMP Chair: Patrycja Paruch, University of Geneva Room: D133-D134 |
Monday, March 15, 2010 11:15AM - 11:27AM |
B24.00001: Strain-stabilizing new functionalities in BiMnO$_3$ and BiFeO$_3$ Alison Hatt, Nicola Spaldin, Claude Ederer Here we present first principles calculations of new functional phases of BiFeO$_3$ and BiMnO$_3$ stabilized by strain in thin film geometries. In BiFeO$_3$ we examine a supertetragonal-like phase recently identified in films grown on LaAlO$_3$ and YAlO$_3$ substrates.\footnote{B\'{e}a {\em et al.}, Phys. Rev. Lett. {\bf 102}, 2009.}$^,$\footnote{Zeches {\em et al.}, Science {\bf 326}, 2009.} We characterize the transition as a function of strain and find that it occurs between phases that are isosymmetric yet have dramatically different structures and properties, the most notable of which is a strong enhancement and rotation of the electric polarization.\footnote{Hatt {\em et al.}, arXiv:0909.4979.} From our computational results we suggest a model for the development of coexisting phases found in BiFeO$_3$ films on LaAlO$_3$ substrates.\footnote{Zeches {\em et al.}, Science {\bf 326}, 2009.} In BiMnO$_3$ we demonstrate strain stabilization of an orbital ordering that gives rise to unusual ferroelectric and magnetic properties. [Preview Abstract] |
Monday, March 15, 2010 11:27AM - 11:39AM |
B24.00002: Substrate and crystal orientation dependent structural and ferroelectric properties of Sm doped BiFeO$_{3}$ thin films at the morphotropic phase boundary Daisuke Kan, Valanoor Nagarajan, Ichiro Takeuchi Previously, we had reported on the universal trend in structural transition in rare-earth-doped BiFeO$_{3}$ films grown on (100) SrTiO$_{3}$ substrates [1]. At this boundary, we observe double hysteresis loops in PE hysteresis loops due to an electric-field-induced transition and substantial enhancement in dielectric constant and piezoelectric coefficient. In this study, we have investigated substrate dependence of the structural and ferroelectric properties of (Bi,Sm)FeO$_{3}$ by growing the composition spreads on various substrates. We chose (100), (110) and (111) SrTiO$_{3}$, (100) LSAT and (110) DyScO$_{3}$ as substrates. Scanning x-ray diffraction reveals that all the fabricated spread films exhibit the rhombohedral to orthorhombic structural transition at Sm 14\%, independent on the type of the substrates. This confirms that the observed structural transition is a bulk property of the (Bi,Sm)FeO$_{3}$ system. The detailed correlations between the structural properties and ferroelectric properties depending on the type of the substrate will be discussed. This work is supported by DMR, NSF MRSEC DMR, ARO and the W. M. Keck Foundation.\\[4pt] [1] S. Fujino et al., APL 92, 202904 (2008). [Preview Abstract] |
Monday, March 15, 2010 11:39AM - 11:51AM |
B24.00003: Synchrotron X-ray Study of Thin Film Samarium Doped BiFeO3 at the Morphotropic Phase Boundary Samuel Emery, Barrett Wells, Ching-Jung Cheng, Nagarajan Valanoor, Daisuke Kan, Ichiro Takeuchi Samarium doped bismuth ferrite (BSFO) is a good lead free candidate for piezoelectric applications. For Sm concentrations of $\sim $14{\%}, BSFO is at a morphotropic phase boundary (MPB) between two structural phases much like lead zirconium titanate (PZT). We have conducted a high resolution synchrotron x-ray diffraction study of Sm doped BiFeO3 films at a composition near the MPB. Films of varying thicknesses were studied over a temperature range of 25C to 700C. We found that the mixed phases associated with the MPB vary with temperature and thickness, indicating that they undergo a transition near 275C. Fundamental lattice constants were measured as a function of temperature; additionally this allowed us to probe structural twins. Also, thermal history dependence was found that indicates a chemical change occurring above film growth temperature. [Preview Abstract] |
Monday, March 15, 2010 11:51AM - 12:03PM |
B24.00004: Understanding Magnetism at the Isostructural Phase Boundary in Multiferroic BiFeO3 Qing He, S.-Y. Yang, R. Ramesh, H.-J. Lin, C.-H. Wang, Y.-H. Chu Recent study suggests that in BiFeO$_{3 }$ (BFO) thin films epitaxial strain can lead to an isostructural change from distorted rhombohedral to a distorted tetragonal structure. In this work, ferromagnetic (or pyromagnetic) phase boundaries between these two phases in BFO thin films are induced from the as-grown state or by applying electric field using piezo- response force microscopy. Rhombohedral-like BFO is a G-type antiferromagnet with its easy plane in (111)-type planes. In depth density functional theory calculations suggest that tetragonal-like BFO is a C-type antiferromagnet with its easy plane in (110)-type planes. Detailed antiferromagnetic ordering of tetragonal-like BFO has been carefully studied using photo- emission electron spectroscopy with linear polarized x-rays. The isostructural phase boundary is magnetically frustrated because the transition between G-type and C-type antiferromagnetic ordering. X-ray magnetic circular dichroism is observed using photo-emission electron microscopy and spectroscopy with circular polarized x-ray. [Preview Abstract] |
Monday, March 15, 2010 12:03PM - 12:15PM |
B24.00005: Origin and Dynamics of Morphotropic Phase Boundary in Multiferroic Films Jinxing Zhang, Robert Zeches, Guang Sheng, Jan Seidel, Pu Yu, Qing He, Chanho Yang, Yinghao Chu, Longqing Chen, Ramamoorthy Ramesh Materials with morphotropic phase boundary (MPB) compositions attract people's interests because of their huge electromechanical response. The ambiguity of crystal structure, phases and physics behind presents a challenge to interpret the origin of abnormally high piezoelectric coefficient. Recently, epitaxial strain can be used to stabilize the MPB in BiFeO$_{3}$. [1] However, to better understand the origin of MPB in multiferroic perovskite, it is essential to probe into the strain/polarization coupling mechanism. In this abstract, origin and dynamics of the phase transition in BiFeO$_{3}$ near MPB have been investigated by exploring the ferroelectric domains. Careful analysis of domain configurations across the phase boundary reveals the rotation of ferroelectric vectors from phase to phase, a new strain/polarization coupling state in nature. The phase transition dynamics are assisted by the re-orientation of ferroelectric polarizations. Phase-field simulation further proves the origin of this MPB is the strain-driven rotation and re-orientation of ferroelectric vectors. This investigation provides new insight into the study of high electromechanical response in MPB-like crystal and helps engineer other lead free-ferroelectrics. Reference: 1. R. J. Zeches, et al., Science 326, 977 (2009). [Preview Abstract] |
Monday, March 15, 2010 12:15PM - 12:27PM |
B24.00006: Optical properties of tetragonal and nanoscale BiFeO$_3$ P. Chen, X. S. Xu, J. L. Musfeldt, A. C. Santulli, C. Koenigsmann, S. S. Wong, N. J. Podraza, A. Melville, E. Vlahos, V. Gopalan, D. G. Schlom, R. Ramesh We measured the optical properties of tetragonal thin film and nanoscale rhombohedral BiFeO$_3$ in the range from near infrared to the near ultraviolet. The absorption spectrum in the tetragonal film is overall blue-shifted compared with that of the rhombohedral BiFeO$_3$ film. It shows an absorption onset near $2.25$ eV, a direct $3.1$ eV band gap, and charge transfer excitations that are $\sim$0.4 eV higher than those of the rhombohedral counterpart. In the nanoparticles, the band gap decreases from $2.7$ eV to $\sim$2.3 eV, and the well-known $3.2$ and $4.5$ eV charge transfer excitations split into multiplets. We discuss these results in terms of structural strain, surface strain, and local symmetry breaking. [Preview Abstract] |
Monday, March 15, 2010 12:27PM - 12:39PM |
B24.00007: Epitaxial-strain-induced multiferroicity in SrMnO$_{3}$ from first principles Jun Hee Lee, Karin M. Rabe In the first-principles search for new ferromagnetic-ferroelectric multiferroics, one key indicator is the softening of the lowest frequency polar phonon with ferromagnetic ordering from a paraelectric antiferromagnetic bulk state. In a first-principles survey of the phonon dispersions of a wide range of magnetic perovskites, we identified SrMnO$_3$ as a promising candidate system. We find that a ferromagnetic-ferroelectric phase is stabilized by both compressive and tensile epitaxial strain. For compressive strain, there is a sequence of intermediate magnetic transitions, first to $C$-AFM and then to $A$-AFM ordering, with an increasing fraction of ferromagnetically aligned nearest neighbor Mn. At each of these, the change in magnetic order is accompanied by a jump in the magnitude of the electric polarization, so, near the $A$-AFM-FE$\rightarrow$FE-FM phase boundary at 3.4\% and $G$-AFM-FE$\rightarrow$FE-FM phase boundary at -2.9\%, an applied electric field can induce a nonzero magnetization, and the jump in $c$-lattice constant at -2.9\% strain can generate a large piezomagnetic response. The origin of the large phonon softening in SrMnO$_3$ will be examined, which should provide guidance in identifying additional candidate systems for epitaxial-strain-induced multiferroicity. [Preview Abstract] |
Monday, March 15, 2010 12:39PM - 12:51PM |
B24.00008: Optically-probed polarization in ultrathin epitaxial YMnO$_{3}$ films Zhigao Sheng, Naoki Ogawa, Yasushi Ogimoto, Kenjiro Miyano The critical thickness has been a fundamental issue in thin films of ferroelectric materials--the absence of which was recently predicted theoretically for improper ferroelectric materials of hexagonal YMnO$_{3}$ (YMO). [1] Here we report second harmonic generation (SHG) studies on YMO ultrathin films, revealing experimentally this prediction. The YMO ultrathin films were deposited on YSZ (111) substrates by pulsed laser ablation. The samples were single crystalline having atomically flat surfaces and epitaxial relation ([10-10]$_{YMO }$//[-110]$_{YSZ})$, as characterized by \textit{in-situ} RHEED, AFM, XRD, and HR-TEM. It is found that even a film with 1.5-unit-cell thickness shows substantial SHG intensity, indicating the existence of spontaneous polarization. In addition to the polarization along the $c$-axis, we found in-plane components which are not observed in single crystals. The details of the crystallographic symmetry and possible origins of the in-plane components will be discussed. \\[4pt] [1] N. Sai, \textit{et al}., Phys. Rev. Lett. \textbf{102}, 107601 (2009). [Preview Abstract] |
Monday, March 15, 2010 12:51PM - 1:03PM |
B24.00009: Electrically controlled magnetization in a tricolor superlattice Alex Demkov, Jaekwang Lee, Na Sai With recent breakthroughs in fabricating high-quality oxide films, ultra thin ferroelectric (FE) films have attracted significant attention. Many FE-based electronic devices proposed to date have a capacitor configuration, where a FE layer is inserted between two identical metal electrodes. We consider theoretically so-called tricolor structures or asymmetric capacitors with one electrode being ferromagnetic and other normal metal. An interesting aspect of a tricolor structure is breaking of the inversion symmetry which is expected to generate new properties. Of particular interest is the control of the magnetization in a ferromagnetic layer without using an external magnetic field. The effect may find applications in low-power and high-density integration in future spintronics devices. To investigate the polarization-dependent magnetization change in the iron layer we construct the tricolor superlattices comprised of Fe/BaTiO$_{3}$/Pt, Fe/PbTiO$_{3}$/Pt and perform first principles calculations at the LSDA+U level. We find the electrode magnetization sensitive to the polarization direction in the FE layer, which suggests a multiferroic character of the structure. The effect is much stronger than in the analogous symmetric structures. We also investigate the change of the depolarization field and screening length due to the lattice relaxation. [Preview Abstract] |
Monday, March 15, 2010 1:03PM - 1:15PM |
B24.00010: Electrical and Optical Study of Multiferroic Superlattices Sandra Dussan, Ashok Kumar, Ram Katiyar Highly oriented superlattices (SL) of ferroelectric (piezoelectric) PbZr$_{0.52}$Ti$_{0.48}$O$_{3}$ (PZT) and ferromagnetic La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) materials were grown on LaAlO$_{3}$ (100) substrates by pulsed laser deposition technique. The x-ray diffraction patterns of PZT/LSMO superlattices with different periodicity evidenced satellite peaks suggest the formation of SL without any secondary parasite phases. Surface topography showed well defined grain with surface roughness $\sim $2-5nm. Grain size and surface roughness changes with change of periodicity. Room temperature magnetization-field (M-H) exhibit well-shaped magnetization hysteresis loops good saturation and low coercivity. The structural, electrical and magnetic properties were studied. Polarized Raman Spectra showed soft transverse and longitudinal modes at 123 cm$^{-1}$ which soften near the ferroelectric phase transition of SLs. The electrical studies were conducted to understand the frequency and temperature dependent dielectric anomalies around to metal-ferromagnetic to insulator-paramagnetic transition temperature of LSMO. [Preview Abstract] |
Monday, March 15, 2010 1:15PM - 1:27PM |
B24.00011: Strain-induced ferroelectricity in simple rocksalt binary oxides Eric Bousquet, Nicola Spaldin, Phillipe Ghosez Rock salt binary AO oxides form an important family of compounds which was intensively studied, both experimentally and theoretically. In comparison to multifunctional ferroelectric perovskite oxides, their practical applications remain however limited and the emergence of ferroelectricity and related functional properties in simple binary oxides seems so unlikely that it was never previously considered. Here, we first show from first-principles density functional calculations that ferroelectricity can be easily induced in simple alkaline earth binary oxides such as BaO using appropriate epitaxial strains. We point out that the functional properties (polarization, dielectric constant and piezoelectric response) of such strained binary oxides are comparable in magnitude to those of typical ferroelectric perovskite oxides, so making them of direct interest for applications. Going further, we also show the possibility to induce ferroelectricity in the ferromagnetic rock salt binary oxides EuO, and so suggesting a new route to achieve multiferroism at high temperature by combining ferroelectric and magnetic properties in very simple structures. [Preview Abstract] |
Monday, March 15, 2010 1:27PM - 1:39PM |
B24.00012: Anisotropic electrical and magnetic properties of epitaxial Ga$_{2-x}$Fe$_{x}$O$_{3}$ thin films with different crystalline orientations Ji Hye Lee, William Jo Anisotropy of electrical and magnetic properties in magnetoelectric and multiferroic materials is an important issue for applications of the materials to electronic devices. Ga$_{2-x}$Fe$_{x}$O$_{3}$ (GFO) has been known as a pyroelectric ferrimagnet at room temperature when x $>$ 1.4. GFO exhibits a permanent polarization along $b$-axis while a spontaneous net magnetization along $c$-axis. Exploration of its anisotropic properties requires preferentially oriented epitaxial thin films of GFO with different crystalline orientations. We have grown successfully $b$-axis oriented GFO thin films on indium-tin oxide(001)/yttria-stabilized zirconia(001). Two additional bottom electrodes such as SrRuO$_{3}$ on SrTiO$_{3}$(111), (110) and (100) and Pt(111)/Ti/SiO$_{2}$/Si substrates were used for epitaxial growth of GFO. X-ray diffraction and transmission electron microscopy have been performed. Dielectric permittivity of the GFO films was measured with external magnetic field as a function of temperature. Local polarization switching behavior was characterized by scanning probe microscopy, which can give a clue to answer a debating question that GFO thin films are pyroelectric with no bistable switching states. [Preview Abstract] |
Monday, March 15, 2010 1:39PM - 1:51PM |
B24.00013: Multiferroic study of PbZr$_{0.53}$Ti$_{0.47}$O$_{3}$/PbFe$_{2/3}$W$_{1/3}$O$_{3}$ Thin Films on various substrates Ashok Kumar, J.F. Scott, Ram S. Katiyar Magnetoelectric (ME) multiferroics (MF), which display simultaneous magnetic, electric, and ferroelastic ordering with their coupling, have drawn increasing interest due to their multi-functionality. Recently we have discovered a novel single phase xPb(Fe$_{2/3}$W$_{1/3})$O$_{3}$ (PFW)/(1-x)PbZr$_{0.53}$Ti$_{0.47}$O$_{3}$ (PZT) (x=0.20) materials which showed room temperature multiferroic properties. Various compositions of PFW/PZT (x =0.20-0.80) thin films were fabricated on single crystalline (STO, LSAT, MgO, Si (100) substrates. All these films showed good ferroelectric and ferromagnetic properties at room temperature. Their ferroelectric to relaxor ferroelectric properties varies with increase of PFW compositions. Their magnetizations also increase with increasing iron concentrations. Substrates with higher lattice mismatch showed better tetragonality hence higher polarization. The single crystalline thin films with 0.20 $\le $ x $\le $ 0.50 showed very high polarization $\sim $ 55 $\mu $C/cm$^{2}$, very high piezo electric response, and well saturated ferromagnetism at room temperature. [Preview Abstract] |
Monday, March 15, 2010 1:51PM - 2:03PM |
B24.00014: Synthesis and characterization of novel room temperature single phase multiferroics Dilsom Sanchez, Ashok Kumar, Ram S. Katiyar Room temperature single phase multiferroics (MF) thin films of Pb(Zr0.$_{53}$Ti$_{0.47})_{1-x}$(Fe$_{0.50}$Ta$_{0.50})_{x}$O$_{3}$(PZFT) (x= 0.10, 0.20, 0.30, 0.40) were fabricated by pulse laser deposition technique (PLD). Surface topography of these films showed well defined grain with average grain size $\sim $ 20 -100 nm, the grain size increases with increase in Ta and Fe compositions. The surface roughness ($\sim $ 2-8 nm) also increases with increase in Fe and Ta compositions. All of these films indicated low dielectric loss, low leakage current, and high dielectric constant. The dielectric constant maximum temperature shifted to lower temperature with increase in iron and tantalum concentrations. The magnetization vs. applied magnetic field (M-H) curves showed well defined hysteresis with remanent magnetization (M$_{r} \quad \sim $ 0.004- 0.13 emu/gm) and very small coercive field (900 Oe). The AC and DC conductivities of PZTFT showed very low conductivity ($\sim $ 10$^{-9 }$to 10$^{-7}$ S/cm$^{-1})$ at room temperature. These films displayed very high polarization $\sim $ (60- 75 $\mu $C/cm$^{2})$ at room temperature. [Preview Abstract] |
Monday, March 15, 2010 2:03PM - 2:15PM |
B24.00015: Investigation of EuO Thin Films Adrian Swartz, J. Wong, Yan Li, J. Ciraldo, R.K. Kawakami EuO is an interesting material for magnetism and spintronics applications due to its large magneto-optic effects, metal-to-insulator transition, and spin splitting of the conduction band. While bulk EuO was extensively studied as long as 40 years ago, epitaxial and stiochiometric films have been difficult to produce. We report the growth of the magnetic insulator EuO on Yttrium Stabilized Zirconia (YSZ 100) and GaAs (001) by reactive Molecular Beam Epitaxy (MBE). The growth is achieved in a regime in which excess Eu ions are re-evaporated and the ratio of Europium to Oxygen flux is more than one. Magneto-Optic Kerr Effect (MOKE) demonstrates a transition for all films at 69K. Further, we investigate the optical and transport properties of these films as well as temperature dependence. [Preview Abstract] |
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