Bulletin of the American Physical Society
Mid-Atlantic Section Fall Meeting 2020
Volume 65, Number 20
Friday–Sunday, December 4–6, 2020; Virtual
Session C04: Polar Materials & Multiferroics |
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Chair: Janice Musfeldt, University of Tennessee |
Friday, December 4, 2020 4:30PM - 5:06PM |
C04.00001: Detailed Structure of Hybrid Improper Ferroelectric Ca$_{\mathrm{3}}$X$_{\mathrm{2}}$O$_{\mathrm{7}}$ Systems Invited Speaker: TREVOR TYSON In hybrid improper ferroelectric systems, polarization arises from the onset of successive nonpolar lattice modes. Detailed measurements and modeling were performed to determine the spatial symmetries of the phases involved in the transitions to these modes. Structural and optical measurements reveal that the tilt and rotation distortions of the MnO$_{\mathrm{6}}$ or TiO$_{\mathrm{6}}$ polyhedra relative to the high symmetry phases driving ferroelectricity in the hybrid improper Ca$_{\mathrm{3}}$X$_{\mathrm{2}}$O$_{\mathrm{7}}$ system (X$=$Mn and Ti) condense at different temperatures. The tilt angle vanishes abruptly at T$_{\mathrm{T}}$ \textasciitilde 400 K for Ca$_{\mathrm{3}}$Mn$_{\mathrm{2}}$O$_{\mathrm{7}}$ (and continuously for X$=$Ti) and the rotation mode amplitude is suppressed at much higher temperatures T$_{\mathrm{R}}$ \textasciitilde 1060 K. Moreover, Raman measurements in Ca$_{\mathrm{3}}$Mn$_{\mathrm{2}}$O$_{\mathrm{7}}$ under isotropic pressure reveal that the polyhedral tilts can be suppressed by very low pressures (between 1.4 and2.3 GPa) indicating their softness. These results indicate that the Ca$_{\mathrm{3}}$Mn$_{\mathrm{2}}$O$_{\mathrm{7\thinspace }}$system provides a new platform for strain engineering of ferroelectric properties in film-based systems with substrate-induced strain. Collaborators: S. Liu, H. Zhang, S. Ghose, M. Balasubramanian, Zhenxian Liu, S. G. Wang, Y-S. Chen, B. Gao, J. Kim, and S.-W. Cheong [Preview Abstract] |
Friday, December 4, 2020 5:06PM - 5:18PM |
C04.00002: High-Resolution In-situ Synchrotron X-ray Studies of Inorganic Perovskite CsPbBr$_{\mathrm{3}}$: New Symmetry Assignments and Structural Phase Transitions. Sizhan Liu, Alexander DeFilippo, Mahalingam Balasubramanian, Zhenxian Liu, SuYin Grass Wang, Yu-Sheng Chen, Stella Chariton, Vitali Prakapenka, Jovan San Martin, Yixiong Lin, Yong Yan, Sanjit Ghose, Trevor Tyson Perovskite photovoltaic systems are being studied due to their high energy conversion efficiencies with current emphasis on pure inorganic systems such as CsPbBr$_{\mathrm{3}}$. In light of the inconsistency of existing space group assignments with recent experiments on this perovskite, high-resolution in-situ synchrotron single-crystal X-ray diffraction and local structure measurements complemented by optical and calorimetric measurements are used to explore the changes in atomic structure for temperatures between 100 and 500 K. The currently accepted space group assignments for CsPbBr$_{\mathrm{3}}$ are found to be incorrect in a manner that profoundly impacts physical properties. The newly observed structural distortions of the bulk structure are consistent with the expectation of previous photoluminescence and Raman measurements. The new derived orthorhombic structure supports can support a ferroelectric state below room temperature. Multiple low-pressure phases are found, one of which exists as a metastable phase at ambient pressure. This work is supported by NSF Grant No. DMR-1809931. [Preview Abstract] |
Friday, December 4, 2020 5:18PM - 5:30PM |
C04.00003: Highly Tunable Ferroelectricity in Hybrid Improper Ferroelectric Sr$_{\mathrm{3}}$Sn$_{\mathrm{2}}$O$_{\mathrm{7}}$ Xianghan Xu, Yazhong Wang, Fei-Ting Huang, Kai Du, Elizabeth Nowadnick, Sang-Wook Cheong The theoretical and experimental success in hybrid improper ferroelectricity (HIF) shed light on a novel way to couple polarization with other physical properties. However, switching the polarization efficiently still remains highly challenging, mainly due to the large energy barrier of oxygen cage movements and pinning/leakage from grain boundaries. Here, we show that the high-quality Sr$_{\mathrm{3}}$Sn$_{\mathrm{2}}$O$_{\mathrm{7}}$ single crystal exhibits the smallest coercive field among all explored HIFs. Remarkably, the 90$^{\mathrm{o}}$ polarization domains can be easily created/erased by a tiny stress at room temperature. In addition, abundant charged domain walls are observed in both pristine and new-created regions. Consistently, DFT calculation indicates a 90$^{\mathrm{o}}$ intermediate step with a small energy barrier in between 180$^{\mathrm{o}}$ polarization switching. Our observations open up several important directions for future exploration-- such as charged domain walls manipulated by stress and the possibility of fast-writable-erasable ferroelectric memorial devices by electrical/mechanical excitations. [Preview Abstract] |
Friday, December 4, 2020 5:30PM - 5:42PM |
C04.00004: Novel Multiferroic triangular lattice antiferromagnet RbFe(SO$_{\mathrm{4}})_{\mathrm{2}}$ Dimuthu Obeysekera, Sabine Neal, William Ratcliff, Janice Musfeldt, Sizhan Liu, Trevor Tyson, Junjie Yang RbFe(SO$_{\mathrm{4}})_{\mathrm{2}}$ (RFSO) crystallizes in the space group of P-3. The magnetic Fe ions in RFSO form an antiferromagnetic triangular lattice. We have synthesized large high-quality anhydrous crystals of RFSO for the first time utilizing hydrothermal method. We characterized the basic magnetic and ferroelectric properties and utilized single crystal synchrotron X-ray diffraction and neutron diffraction to determine the nuclear structure and magnetic structure of RFSO. Raman measurements were also carried out on the RFSO sample. In this talk, we will discuss the structural and physical properties of the anhydrous magnetic sulfate (RFSO). By summarizing all our experimental results, we have also constructed the phase diagram of RFSO. RFSO is an exciting new candidate for Type-II multiferroic as well as a new type of quantum electromagnet and we will use the results outlined above to discuss how the ferro-rotational order, magnetoelectric coupling and its atomic level structure will give rise unique physics in this material. [Preview Abstract] |
Friday, December 4, 2020 5:42PM - 6:18PM |
C04.00005: Magnetic chirality induced by chemical substitution in a chiral-polar antiferromagnet. Invited Speaker: Junjie Yang Exotic physical phenomena are bound to happen in chiral magnets, since broken space inversion, mirror symmetry and time reversal symmetry often accompany new physical phenomena.$^{\mathrm{\thinspace }}$The Dzyaloshinskii Moriya (\textit{DM}) interactions, allowed by the lattice chirality, could bring about a twist between the magnetic moments and lead to various chiral magnetic structures.$^{\mathrm{\thinspace }}$However, chiral magnets do not necessarily exhibit chiral magnetic structures. For example, the chiral magnet Ni$_{\mathrm{3}}$TeO$_{\mathrm{6}}$ exhibits an achiral collinear antiferromagnetic structure below 52 K. Exploring the new methods that could turn the collinear magnetic structure into chiral magnetic structure in chiral magnets is crucial for studying the exotic chiral physics in this family of materials. Recently, we synthesized high quality single crystals of Co-substituted Ni$_{\mathrm{3}}$TeO$_{\mathrm{6}}$ - NiCo$_{\mathrm{2}}$TeO$_{\mathrm{6}}$. In this talk, we will discuss our recent experimental results of chiral magnet NiCo$_{\mathrm{2}}$TeO$_{\mathrm{6}}$. Our neutron diffraction experiments reveal that an incommensurate helical magnetic structure with spins aligned in the \textit{ab} plane is induced by Co substitution. The results obtained from our polarized neutron diffraction experiments show clear magnetic chirality in the magnetic structure. Our results suggest that chemical substitution is an efficient method for creating chiral magnetic structures in chiral magnets. [Preview Abstract] |
Friday, December 4, 2020 6:18PM - 6:30PM |
C04.00006: Tuning Polarization and Electronic Structure via Chemical Substitution in Two Dimensional Ferroelectrics Joshua Young, Mo Li, Olamide Omisakin Two dimensional materials with switchable spontaneous electric polarizations (``2D ferroelectrics'') have recently been garnering attention as components for ultrathin electronic devices. However, 2D ferroelectrics with out-of-plane polarizations are challenging to find. Recently, Chandrasekaran et al. proposed that the functionalized MXene Sc$_{\mathrm{2}}$CO$_{\mathrm{2}}$ has a metastable state with a large out-of-plane polarization. [1] In this work, we used density functional theory (DFT) calculations to investigate additional M$_{\mathrm{2}}$CX$_{\mathrm{2}}$ materials (M $=$ Sc, Y, La; X $=$ O, F). We found that (1) substitution of Sc with Y and/or O with F can stabilize the ferroelectric phase as the ground state (the dynamic stability was verified with phonon calculations); (2) substitution can also be used to tune the polarization and band gap; and (3) these monolayers display large piezoelectric coefficients. We also show that these properties can be continuously tuned by the application of external strain or by alloying to create Sc$_{\mathrm{2x}}$Y$_{\mathrm{2(1-x)}}$CO$_{\mathrm{2}}$ monolayers. These findings demonstrate that chemical substitution and external stimuli are powerful ways to stabilize and control the properties of low dimensional ferroelectric materials. [1] A. Chandrasekaran, A. Mishra, A. K. Singh, Nano Letters 17 3290 (2017) [Preview Abstract] |
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