Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session X22: Room Termperature Multiferroic BiFeO3Invited
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Sponsoring Units: DCMP GMAG Chair: Randy Fishman, Oak Ridge National Laboratory Room: New Orleans Theater A |
Friday, March 17, 2017 8:00AM - 8:36AM |
X22.00001: Neutron Scattering Measurements on bulk BiFeO$_{\mathrm{\mathbf{3}}} Invited Speaker: Je-Geun Park Of a long list of multiferroic materials, BiFeO$_{\mathrm{3}}$ is arguably one of the most interesting multiferroic materials as it displays rare room-temperature multiferroic behavior: T$_{\mathrm{N}}=$650 K and T$_{\mathrm{C}}=$1050 K. Hence BiFeO$_{\mathrm{3}}$ has been extensively investigated for potential applications. It also has a very interesting incommensurate magnetic phase transition with an extremely long period of 650 {\AA}. In this talk, I will present our latest results [1-4] mainly obtained from high-resolution neutron scattering experiments on this fascinating material. Using the vast amount of the data, I will sketch a coherent picture of the rare room-temperature multiferroic behavior and, most importantly, a full spin Hamiltonian of BiFeO$_{\mathrm{3}}$.\\ \\$[1]$ Jaehong Jeong, et al., Phys. Rev. Lett. 108, 077202 (2012)\newline [2] Sanghyun Lee et al., Phys. Rev. B Rapid Comm. 88, 060103R (2013)\newline [3] Jaehong Jeong, et al., Phys. Rev. Lett. 113, 107202 (2014)\newline [4] [Review] Je-Geun Park, et al., J. Phys.: Condens. Matter 26, 433202 (2014) [Preview Abstract] |
Friday, March 17, 2017 8:36AM - 9:12AM |
X22.00002: Magnetic and electric control of multiferroic properties in monodomain crystals of BiFeO$_{3}$ Invited Speaker: Masashi Tokunaga One of the important goals for multiferroics is to develop the non-volatile magnetic memories that can be controlled by electric fields with low power consumption. Among numbers of multiferroic materials, BiFeO$_{3}$ has been the most extensively studied because of its substantial ferroelectric polarization and magnetic order up to above room temperature [1]. Recent high field experiments on monodomain crystals of BiFeO$_{3}$ revealed the existence of additional electric polarization normal to the three-fold rotational axis [2]. This transverse component is coupled with the cycloidal magnetic domain, and hence, can be controlled by external magnetic fields. Application of electric fields normal to the trigonal axis modifies volume fraction of these multiferroic domains, which involves change in resistance of the sample, namely exhibits the bipolar resistive memory effect [3]. In this talk, I will introduce the effects of magnetic and electric fields on magnetoelectric and structural properties observed in monodomain crystals of BiFeO$_{3}$. REFERENCES: [1] G. Catalan and J. F. Scott, Adv. Mater. 21, 2463 (2009). [2] M. Tokunaga \textit{et al.}, Nature Commun. \textbf{6}, 5878 (2015). [3] S. Kawachi \textit{et al}. Appl. Phys. Lett. \textbf{108}, 162903 (2016). [Preview Abstract] |
Friday, March 17, 2017 9:12AM - 9:48AM |
X22.00003: Unidirectional THz radiation propagation in BiFeO3. Invited Speaker: Toomas Room The mutual coupling between magnetism and electricity present in many multiferroic materials permit the magnetic control of the electric polarization and the electric control of the magnetization. These static magnetoelectric (ME) effects are of enormous interest: The ability to write a magnetic state current-free by an electric voltage would provide a huge technological advantage. However, ME coupling changes the low energy electrodynamics of these materials in unprecedented way -- optical ME effects give rise to unidirectional light propagation as recently observed in low-temperature multiferroics. The transparent direction can be switched with dc magnetic or electric field, thus opening up new possibilities to manipulate the propagation of electromagnetic waves in multiferroic materials. We studied the unidirectional transmission of THz radiation in BiFeO3 crystals, the unique multiferroic compound offering a real potential for room temperature applications. The electrodynamics of BiFeO3 at 1THz and below is dominated by the spin wave modes of cycloidal spin order. We found that the optical magnetoelectric effect generated by spin waves in BiFeO3 is robust enough to cause considerable nonreciprocal directional dichroism in the GHz-THz range even at room temperature. The supporting theory attributes the observed unidirectional transmission to the spin-current-driven dynamic ME effect. Our work demonstrates that the nonreciprocal directional dichroism spectra of low energy excitations and their theoretical analysis provide microscopic model of ME couplings in multiferroic materials. Recent THz spectroscopy studies of multiferroic materials are an important step toward the realization of optical diodes, devices which transmit light in one but not in the opposite direction. [Preview Abstract] |
Friday, March 17, 2017 9:48AM - 10:24AM |
X22.00004: Giant spin-induced polarization and optical-diode effect by electromagnons in BiFeO$_{\mathrm{3}}$ Invited Speaker: Jun Hee Lee Type-$I$ multiferroics where spin and electric polarization order at distinct temperatures were believed to have smaller couplings between them compared to type-\textit{II} multiferroics such as TbMnO$_{\mathrm{3}}$. However, we recently discovered unexpectedly huge couplings between spin and electric polarization in representative type-$I$ multiferroic BiFeO$_{\mathrm{3}}$. This hidden coupling leads to record-high spin-induced ferroelectric polarizations (\textasciitilde 3.0 $\mu $C/cm$^{\mathrm{2}})$ [1] which is one or two order larger than in any other multiferroics. Also, the spin-polarization couplings in \textit{dynamic} region [2] generates strong electromagnons resulting in sizable one-way optical transparency at the spin-wave excitations [3]. Overall, we show how our theoretical results revive studies in revealing hidden but huge spin-polarization couplings and their dynamic interactions with light in type-$I$ multiferroics. [1] J. H. Lee and R. Fishman, Physical Review Letters, 115, 207203 (2015). [2] \quad J. H. Lee, I. Kezsmarki, and R. Fishman$, $New Journal of Physics 18, 043205 (2016). [3] R. Fishman, J. H. Lee \textit{et al}., Physical Review B, 92, 094422 (2015). *This work has been done by collaborations with R. Fishman (ORNL) and I. Kezsmarki (U of Budapest). [Preview Abstract] |
Friday, March 17, 2017 10:24AM - 11:00AM |
X22.00005: Electric-field control of magnetism and magnons in the room temperature multiferroic BiFeO$_3$ Invited Speaker: Rog\'{e}rio de Sousa The ability to control magnetism using electric fields is of great fundamental and practical interest. It may allow the development of ideal magnetic memories with electric write and magnetic read capabilities, as well as logic devices based on magnons that dissipate much less energy. The application of an external $E$ field to bulk magnetoelectric bismuth ferrite (BiFeO$_3$ or BFO) was shown to lead to a giant shift of magnon frequencies that is linear in $E$ and $10^{5}$ times larger than any other known $E$-field effect on magnon spectra [1]. I will present a theory of this effect based on the combination of multiferroicity with strong spin-orbit interaction, and show that it enables $E$-field control of BFO's magnetic state [2]. The application of moderate external $E$ and $B$ fields at appropriate orientations enable competing magnetoelectric interactions to interfere in such a way that the system transitions from a cycloid to a homogeneous state at much lower field values than if only one type of field was applied. These results clarify the conditions required to make BFO a useful material in device applications, and shed light on experiments where BFO is interfaced with other magnetic and ferroelectric materials.\\ \\ \noindent[1] P. Rovillain {\it et al.}, Nat. Mater. {\bf 9}, 975 (2010).\\ \noindent[2] R. de Sousa, M. Allen, and M. Cazayous, Phys. Rev. Lett. {\bf 110}, 267202 (2013). [Preview Abstract] |
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