Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session Q18: Focus Session: Magnetic Oxide Thin Films - Multiferroic Thin Films |
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Sponsoring Units: DMP GMAG Chair: Lane Martin, University of Illinois at Urbana-Champaign Room: D172 |
Wednesday, March 23, 2011 11:15AM - 11:51AM |
Q18.00001: Enhanced magnetoelectric effects via strain engineering and structural softness Invited Speaker: After describing a general theory of the magnetoelectric response, I will argue that inducing {\em structural softness} -- i.e., tuning a material so that it takes a small amount of energy to distort its structure -- constitutes a general and robust strategy to obtain very large effects. Further, I will argue that this design strategy will be effective at room temperature, and will not affect other desirable properties of the materials (i.e., their insulating character). I will illustrate this possibility with first-principles results for thin films of room-temperature multiferroic BiFeO$_3$, where the structural softness is induced by epitaxial strain. I will also present results for BiFeO$_3$-based solid solutions, discussing several alternative mechanisms by which their electromechanical and magnetoelectric responses can be enhanced. Finally, I will discuss the prospect of inducing in BiFeO$_3$ a so-called {\em morphotropic phase boundary}, where the material is expected to display very large functional responses in analogy to what occurs in strong piezoelectric PbZr$_{1-x}$Ti$_{x}$O$_{3}$. [Preview Abstract] |
Wednesday, March 23, 2011 11:51AM - 12:03PM |
Q18.00002: Electrically Controllable Magnetism in Strained BiFeO$_3$ Thin Films Qing He, W. Luo, R. Ramesh, J.-C. Yang, Y.-H. Chu, A. Scholl multiferroic BiFeO$_3$ (BFO) thin films epitaxial strain can lead to the formation of a mixed phase system -- highly distorted rhombohedral (R') and distorted tetragonal (super-tetragonal) (T) phases. Interestingly, this R' phase has been observed to be with enhanced magnetization compare to bulk BFO. Then, in order to investigate the origin of the magnetism in R' phase, synchrotron x-ray absorption, and x-ray (magnetic) circular/linear dichroism have been employed with assistance of spectra simulation and the ferroelectric, antiferromagnetic and ferromagnetic properties of this magnetic R' films have been clearly identified. Surprisingly, enhanced magnetization emerges in (001) plane as soon as a critical DC field is applied to the film in $<001>$ direction. The key is that the movement of Fe$^{3+}$ can be controlled by external electric field, which magnifies the effect of Dzyaloshinsky-Moriya interaction to the system, and enlarges the canting magnetic moment of Fe spins. Finally, the direction of the local magnetic moment can be deterministically by external electric field will be demonstrated. [Preview Abstract] |
Wednesday, March 23, 2011 12:03PM - 12:15PM |
Q18.00003: Origin of Reversible Electric Exchange Bias Modulation in a Multiferroic Field Effect Device Stephen Wu, Shane Cybart, Pu Yu, R. Ramesh, R.C. Dynes We report the fabrication and characterization of two different oxide heterostructure based electric field effect devices: the multiferroic/ferromagnet, BiFeO$_{3 }$(BFO) / La$_{0.7}$Sr$_{0.3}$MnO$_{3 }$(LSMO) and the ferroelectric/ferromagnet, Pb(Zr$_{0.2}$Ti$_{0.8})$O$_{3}$(PZT)/LSMO. By switching FE polarization of BFO in the multiferroic device we observe a change in conductivity in the channel of 50{\%}, and a 55{\%} change in magnetic coercivity at 5.5 K. Furthermore, we can reversibly switch between two distinct exchange bias states corresponding to the different FE polarizations without additional field cooling. The difference in exchange bias between the two states is approximately 20mT. We further characterize the device by performing Hall Effect and temperature dependent exchange bias modulation measurements. Finally, we compare this device to a similarly fabricated PZT/LSMO field effect device. We observe no exchange bias and significantly smaller coercivity. No change in magnetic coercivity is observed when ferroelectric polarization is switched in PZT. Models based on these results will be presented. [Preview Abstract] |
Wednesday, March 23, 2011 12:15PM - 12:27PM |
Q18.00004: Electrical Transport Measurements of a Manganite Multiferroic Field Effect Device James Parker, Shane Cybart, Stephen Wu, Pu Yu, R. Ramesh, R.C. Dynes We report electrical transport measurements of multiferroic/ferromagnet, BiFeO3 (BFO) / La0.7Sr0.3MnO3 (LSMO), electric field effect devices. The antiferromagnetic (AFM) ordering of the BFO dielectric layer is coupled to the ferromagnetic (FM) ordering of the LSMO channel layer and is observed as exchange bias --a shift of the LSMO magnetic hysteresis curve along the applied field axis. We will present the temperature dependence of this exchange bias between 2K and 100K. Furthermore, we also investigate the exchange bias with respect to multiple gating variables, including channel current and gate pulsing patterns. We have observed that the current in the channel during gating plays an important role in setting the exchange bias. [Preview Abstract] |
Wednesday, March 23, 2011 12:27PM - 1:03PM |
Q18.00005: Magnetic Structure of Engineered Multiferroic Thin Films Invited Speaker: The intriguing properties of multiferroics, i.e., materials exhibiting the coexistence of magnetism and ferroelectricity, have stimulated intense research interest in recent years. From the viewpoint of practical applications, one needs to exploit the thin film architectures of multiferroic materials. However, fewer studies have addressed the magnetic structures of multiferroic thin films. I will present recent experimental works on two multiferroic films, BiFeO$_{3}$ and EuTiO$_{3}$, physical properties of which can be engineered via the epitaxial growth on appropriate substrates. Neutron diffraction studies on BiFeO$_{3}$ films deposited on vicinal SrTiO$_{3}$ substrates show that the magnetic structure of these films is closely correlated with the ferroelectric states that depend on the chosen substrate miscut [1]. Epitaxial EuTiO$_{3}$ grown on DyScO$_{3}$ susbtrate, which is a paraelectric antiferromagnet in its bulk form, is strain-tuned into multiferroics, displaying both ferroelectric and ferromagnetic characters [2]. The relationship between the strong magnetic anisotropy and the film microstructure will be discussed. \\[4pt] [1] X. Ke, P. P. Zhang, S. Baek, J. Zarestky, W. Tian, and C. B. Eom, Phys. Rev. B \textbf{82}, 134448 (2010). \\[0pt] [2] J.~H. Lee, L. Fang, E. Vlahos, X. Ke, Y.W. Jung \textit{et al}., Nature \textbf{466}, 954 (2010). [Preview Abstract] |
Wednesday, March 23, 2011 1:03PM - 1:15PM |
Q18.00006: Electric-field control of spin waves at room temperature in multiferroic BiFeO$_{3}$ Maximilien Cazayous, Pauline Rovillain, Yann Gallais, Alain Sacuto, Marie-Aude Measson, Rogerio de Sousa, Dorothee Colson, Anne Forget, Manuel Bibes, Agnes Barthelemy A particularly exciting prospect in the field of spintronics is to use the wave like excitations of a magnetic material as a means to transmit and process information. This technology named magnonics relies on the control of spin waves. The key goal of magnonics is to read/write non-volatile spin information with minimal energy consumption. Multiferroic materials have at least two coupled magnetic and ferroelectric orders leading to electrical control of magnetic effects and vice-versa. Multiferroic materials are thus potentially interesting as a medium for spin-wave-based information processing. Here we show that the spin wave excitations in BiFeO$_{3}$, a room temperature multiferroic can be controlled by an electric field at low power and in a non-volatile way. The present experiment clearly demonstrates spin waves can be tuned over 30{\%} of their frequencies, several orders of magnitude larger than with previous methods. The switch and the control of the polarization is used to manage this tuning. [Preview Abstract] |
Wednesday, March 23, 2011 1:15PM - 1:27PM |
Q18.00007: Electric-field control of spin waves in multiferroic BiFeO3: Theory Rog\'{e}rio de Sousa, P. Rovillain, Y. Gallais, A. Sacuto, M.A. M\'{e}asson, D. Colson, A. Forget, M. Bibes, A. Barth\'{e}l\'{e}my, M. Cazayous Our recent experiment [1] demonstrated gigantic (30\%) electric-field tuning of magnon frequencies in multiferroic BiFeO3. We demonstrate that the origin of this effect is related to two linear magnetoelectric interactions that couple the component of electric field perpendicular to the ferroelectric vector to a quadratic form of the N\'{e}el vector. We calculate the magnon spectra due to each of these interactions and show that only one of them is consistent with experimental data. At high electric fields, this interaction induces a phase transition to a homogeneous state, and the multi-magnon spectra will fuse into two magnon frequencies. We discuss the possible microscopic mechanisms responsible for this novel interaction and the prospect for applications in magnonics.\\[4pt] [1] P. Rovillain, {\it et al.}, Nature Materials advance online publication Nov. 14 2010 (DOI 10.1038/nmat2899), http://dx.doi.org/10.1038/nmat2899 [Preview Abstract] |
Wednesday, March 23, 2011 1:27PM - 1:39PM |
Q18.00008: Ultrafast dynamics in multiferroic BiFeO$_{3}$ Yu-Miin Sheu, Rohit Prasankumar, Antoinette Taylor We report the ultrafast time-resolved optical measurements of multiferroic BiFeO$_{3, }$which exhibits both magnetic and ferroelectric ordering at room temperature. The coupling between these two orders makes it an attractive material for potential data-storage devices. However, a detailed understanding of this coupling is still under debate. Ultrafast optical spectroscopy can potentially shed light on magnetoelectric coupling in BiFeO$_{3}$ by unraveling the different contributions in the time domain. Here, we use degenerate 400 nm pump-probe spectroscopy to excite and probe a BiFeO$_{3}$ thin film above its bandgap. The measured relaxation consists of a fast decay ($\sim $1 ps) followed by a slow recovery ($\sim $150 ps). We attribute the fast component to the recovery of photoexcited carriers. The slow recovery may be due to spin-lattice relaxation. [Preview Abstract] |
Wednesday, March 23, 2011 1:39PM - 1:51PM |
Q18.00009: Substrate induced strain effects on the multiferroism of BiMnO$_{3}$ thin films Hyoung Jeen Jeen, Patrick Mickel, A.F. Hebard, Amlan Biswas, Valentin Craciun BiMnO$_{3}$ is a single phase multiferroic material, which shows ferroelectricity and ferromagnetism at low temperature. However, it is difficult to grow BiMnO$_{3}$ either in bulk or thin film form, since it is metastable with substantial desorption of Bi ions at high growth temperature. Here we have used SrTiO$_{3}$ and SrLaGaO$_{4}$ substrates, which provide different degrees of compressive strain, to stabilize the BiMnO$_{3}$ phase and have introduced fast quenching after deposition in oxygen atmosphere to suppress re-evaporation of Bi-ions but retain film crystallinity. Surface morphology indicates island growth mode. X-ray diffraction (XRD) shows that the BiMnO$_{3}$ [111] is parallel with [001] SrTiO$_{3}$ and [001] SrLaGaO$_{4}$. XRD results confirm that the BiMnO$_{3}$ films on SrTiO$_{3 }$substrates are epitaxial, with in-plane alignment. The films have a magnetization of 1 $\mu _{B}$/Mn at 5 T and 10 K. We also observed ferroelectricity in our BiMnO$_{3}$ films. Based on these results, we will discuss the substrate induced strain effects on the multiferroic properties of BiMnO$_{3}$ thin films. [Preview Abstract] |
Wednesday, March 23, 2011 1:51PM - 2:03PM |
Q18.00010: Room-Temperature Multiferroic Properties of Bismuth Manganite Thin Film W.C. Kuo, C.Y. Kuo, H.J. Liu, H.J. Lin, Y.H. Chu, Y.C. Chen, T.M. Uen, J.Y. Juang In multiferroic materials, low temperature multiferroic properties in perovskite type BiMnO$_{3}$ has been demonstrated. In this work, through epitaxial strains exerted by LaAlO$_{3}$ single crystal substrate, we successfully demonstrate the growth the c-axis oriented new phase in BMO thin film. After the deposition, HRXRD has been used to characterize the lattice structure, which show new fascinating phase that are different from the papers early reported. We further revealed manganese valence through the X-ray Magnetic Linear Dichroism measurement and exhibit the mixed +3 and +4 valence of manganese. With LaNiO$_{3}$ bottom electrode, room-temperature ferroelectricity is demonstrated by piezoelectric force microscopy, which revealed the reversible ferroelastic switching through the external electrical bias. M-H curves are measured by SQUID magnetometer as a function of temperatures. Ferromagnetic behaviors have been probed from room temperature (300K) to low temperature (10K), furthermore, ferromagnetic phenomenon has been observed at 300K. In our preliminary results, room temperature ferroelectric and ferromagnetic properties could be coexistent in single phase material through epitaxial strain, thus provide a modeling system to study the multiferroic material and a powerful candidate for the next- generation electronic devices. [Preview Abstract] |
Wednesday, March 23, 2011 2:03PM - 2:15PM |
Q18.00011: Magnetic field dependence of the spin wave excitations in Sr$_2$FeSi$_2$O$_7$ Kazuki Iida, Jooseop Lee, Naoyuki Katayama, Sungdae Ji, Seunghun Lee, Duc Le, Sung Chang, Taehwan Jang, Yoonhee Jeong, Sangwook Cheong Without field, the multiferroic Sr$_2$FeSi$_2$O$_2$ orders below 4.7 K into a simple square-lattice antiferromagnetic collinear structure. Application of a magnetic field at low temperatures induces four different magnetic phases with spontaneous electric polarization. We report inelastic neutron scattering measurements on a single crystal of Sr$_2$FeSi$_2 $O$_7$ under magnetic fields to investigate how the magnetic fluctuations change with field. In zero field, no dispersion was observed in $L$-direction, indicating that Sr$_2$FeSi$_2 $O$_7$ is a two dimensional magnet. The dispersion relation along ($H$ 0 0.5) shows a Goldstone mode arising from the magnetic Bragg position at (1 0 0.5) with a periodicity of $2 \times2\pi/a$, suggesting that the strongest magnetic interaction is between the nearest neighbor Fe$^{2+}$ ions. Under the field, the magnetic fluctuations become more complex than the simple splitting of the doubly degenerate Goldstone mode into two gapped modes. [Preview Abstract] |
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