Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session V20: Correlated Electron Magnetism and Structural Phase Transitions |
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Sponsoring Units: DCMP GMAG Chair: James Hamlin, University of Florida Room: 280 |
Thursday, March 16, 2017 2:30PM - 2:42PM |
V20.00001: Giant exchange bias effect in YCo$_{\mathrm{0.25}}$Mn$_{\mathrm{0.75}}$O$_{\mathrm{3}}$ compound according to change of ratio by additional Mn ions Sanghyup Oh, Jai Young Moon, Mi Kyung Kim, Nara Lee, Young Jai Choi Recently studied on exchange bias (EB) phenomena in Y$_{\mathrm{2}}$CoMnO$_{\mathrm{6}}$ reveals interfacial exchange coupling between Mn$^{\mathrm{4+}}$-O-Mn$^{\mathrm{4+}}$, Co$^{\mathrm{2+}}$-O-Co$^{\mathrm{2+}}$ antiferromagnetic (AFM) ordering induced by antisite defect and Co$^{\mathrm{2+}}$-O-Mn$^{\mathrm{4+\thinspace }}$ferromagnetic (FM) ordering, while we approached EB effect by additional Mn ion according to change of ratio between Co and Mn ions, successfully made YCo$_{\mathrm{0.25}}$Mn$_{\mathrm{0.75}}$O$_{\mathrm{3}}$ compound. Spin-glass behavior is observed because of complex magnetic properties. We observed that the week FM hysteresis loop is at 2 K, giant exchange bias field, H$_{\mathrm{EB}}$ \textasciitilde 13 kOe, was observed at 2 K in measuring field range ±15 kOe after applied field cooled (FC) in 40 kOe. The observed exchange bias effect reveals the strong dependence on cooling magnetic fields, measuring fields, and temperature. We suggest that the giant EB effect would originate from the interfacial pinning of exchange couplings between not only FM and AFM ordering but also FM and SG areas generated due to Mn$^{\mathrm{3+}}$-O-Mn$^{\mathrm{3+}}$ AFM ordering created by additional Mn ion. [Preview Abstract] |
Thursday, March 16, 2017 2:42PM - 2:54PM |
V20.00002: Physical properties of metallic tetragonal compound Ti$_4$MnBi$_2$ Abhishek Pandey, Mason Klemm, Hua He, Meigan C. Aronson We report the investigation of structural, magnetic, thermal and electrical transport properties of metallic compound Ti$_4$MnBi$_2$ that crystallizes in a tetragonal structure (space group: $I$4/$mcm$) with a large $a = 10.4946(4)$~\AA\ and relatively smaller $c = 4.9860(2)$~\AA\@. The structure of this compounds is quite simple where each of the constituent atoms occupy only one atomic site and contains cylindrical channels of Bi and Ti atoms and linear chains of Mn-ions that stretch along the c-axis of the tetragonal unit cell. This metallic compound does not show any evidence of magnetic ordering and exhibits a Curie-Weiss behavior for $T > 30$~K with an antiferromagnetic (AFM) Weiss temperature $\theta_{\rm p}= -13(1)$~K, suggesting the presence of AFM interactions in the material. Heat capacity $C_{\rm p}(T)$ data exhibit a large value of Sommerfeld coefficient $\gamma \approx 200$~mJ/mol~K$^2$ leading to a very large density of states $D(E_{\rm F}) \approx 85$~states/eV f.u. for both spin directions at the Fermi level $E_{\rm F}$. Our investigation of the structure and property relation in this compound will be discussed. [Preview Abstract] |
Thursday, March 16, 2017 2:54PM - 3:06PM |
V20.00003: Magnetic exchange bias effect with magnetization reversal in double perovskite Er$_{\mathrm{2}}$CoMnO$_{\mathrm{6}}$ single crystal Jae Young Moon, Mi Kyung Kim, Sang Hyup Oh, Nara Lee, Young Jai Choi We have successfully synthesized the high-quality single crystals of double perovskite Er$_{\mathrm{2}}$CoMnO$_{\mathrm{6}}$ by the conventional flux method with Bi$_{\mathrm{2}}$O$_{\mathrm{3}}$ flux, and have investigated their magnetic properties and magnetic exchange bias effects. The ferromagnetic order arises at $T_{\mathrm{C}} \quad =$63.5 K from the dominant Co$^{\mathrm{2+}}$ and Mn$^{\mathrm{4+}}$ superexchange interactions, mainly along the $c$ axis. A huge increase in the temperature dependence of specific heat divided by temperature occurs due to the Er$^{\mathrm{3+}}$ spin ordering at $T_{\mathrm{Er}}=$12 K. Magnetization reversal in temperature dependence of magnetic susceptibility and inverted hysteresis loop along the$ c$ axis in magnetic field dependence of magnetization are observed below $T_{\mathrm{Comp}}=$3.15 K, resulted from the interaction between Er$^{\mathrm{3+}}$ and Co$^{\mathrm{2+}}$/Mn$^{\mathrm{4+}}$ sublattices. The exchange bias effects are exhibited in the inverted hysteresis loops, and the maximum exchange bias field of 0.3 kOe is obtained after field cooling in $H_{\mathrm{FC}}=$0.190 kOe. [Preview Abstract] |
Thursday, March 16, 2017 3:06PM - 3:18PM |
V20.00004: Interplay between magnetostructural transformation and magnetocrystalline anisotropy in TbMn$_{\mathbf{2}}$ Manish K. Kashyap, D. Paudyal, B. N. Harmon Using density functional theory (DFT) approach, the magnetostructural phase transformations from paramagnetic cubic to ferrimagnetic rhombohedral structure in ordered and disordered TbMn$_{2}$ Laves phase compounds have been investigated. The calculations of the electronic and magnetic properties of these compounds were performed using the full potential linear augmented plane wave (FPLAPW) method. The added onsite electron correlation in local spin density approximation (LSDA$+U)$ for the occupied and unoccupied 4$f$-states yields a better representation of the bandstructure, density of states, and individual magnetic moments as compared to LSDA alone. Indirect 4$f$-4$f$ exchange interactions and crystal field splitting play a significant role to decide magnetic and structural phases. Our results confirm the magnetocrystalline anisotropy driven rhombohedral ground state in TbMn$_{2}$. [Preview Abstract] |
Thursday, March 16, 2017 3:18PM - 3:30PM |
V20.00005: Vollhardt "invariant" and phase transition in the helical itinerant magnet MnSi Sergei Stishov, Alla Petrova We argue that rounded "hills" or "valleys" demonstrated by the heat capacity, thermal expansion coefficient, and elastic module are indications of a smeared second order phase transition, which is flattened and spread out by the application of a magnetic field. As a result, some of the curves which display a temperature dependence of the corresponding quantities cross almost at a single point. Thus, the Vollhardt crossing point should not be identified with any specific energy scale. The smeared phase transition in MnSi preceding the helical first order transition most probably corresponds to the planar ferromagnetic ordering, with a small or negligible correlation between planes. At lower temperatures, the system of ferromagnetic planes becomes correlated, acquiring a helical twist. [Preview Abstract] |
Thursday, March 16, 2017 3:30PM - 3:42PM |
V20.00006: Mapping of Picoscale Lattice Displacements in Charge Density Wave Systems to Measure Local Symmetry, Elasticity, and Disorder Benjamin H. Savitzky, Ismail El Baggari, Alemayehu Admasu, Jaewook Kim, Sang-Wook Cheong, Robert Hovden, Lena F. Kourkoutis We present direct, local measurement of picometer scale periodic lattice displacements (PLDs) in charge density wave systems using scanning transmission electron microscopy (STEM) data. Our approach combines picometer precision, real-space tracking of atomic nuclei with Fourier analysis to reveal the local symmetry, elasticity, and disorder of emergent lattice ordering. By investigating both manganite oxides and transition metal dichalchogenides, we uncover the atomically resolved lattice response about multiple PLD defect structures, including topological singularities in the PLD phase. We observe elastic deformations of the PLD field, and consider their energetics by isolating the contributions of PLD phase and amplitude variations. Further, we extract maps of individual modulations in the presence of multiple, coexisting modulation vectors, revealing a complex domain structure of locally stripe-ordered regions. Our work isolates and locally interrogates the collective behavior of the atomic lattice in multiple strongly correlated systems, demonstrating a potent new tool for the systematic examination of ordered phases. [Preview Abstract] |
Thursday, March 16, 2017 3:42PM - 3:54PM |
V20.00007: From enhanced paramagnetism to ferromagnetism: the physical properties of Sr$_{\mathrm{1-x}}$La$_{\mathrm{x}}$Co$_{\mathrm{2}}$As$_{\mathrm{2}}$ single crystals Jie Xing, Ni Ni We have successfully synthesized Sr$_{\mathrm{1-x}}$La$_{\mathrm{x}}$Co$_{\mathrm{2}}$As$_{\mathrm{2}}$ single crystals and characterized them through transport and thermodynamic measurements. The enhanced paramagnet SrCo$_{\mathrm{2}}$As$_{\mathrm{2}}$, which has stripe antiferromagnetic fluctuations, shows a metamagnetic phase transition at a critical magnetic field of 2 T at 2 K. When La is doped into the system, the critical field is suppressed to lower field and itinerant ferromagnetism starts building up at x$=$0.4, rising to a TM of \textasciitilde 200 K at x$=$1. The competition between the stripe spin fluctuations and the itinerant ferromagnetism makes Sr$_{\mathrm{1-x}}$La$_{\mathrm{x}}$Co$_{\mathrm{2}}$As$_{\mathrm{2}}$ compounds a particularly interesting system for the study of itinerant magnetism. [Preview Abstract] |
Thursday, March 16, 2017 3:54PM - 4:06PM |
V20.00008: A-site and B-site charge orderings of perovskite PbCoO$_{\mathrm{3}}$ Yuki Sakai, Runze Yu, Hajime Yamamoto, Hajime Hojo, Masaki Azuma, Ikuya Yamada, Junye Yang, Yunyu Yin, Youwen Long, Ping Miao, Sanghyun Lee, Shuki Torii, Takashi Kamiyama Metal ions with half-integer valence tend to split into two integer valence ions and these get spatially ordered as typically observed in La$_{\mathrm{0.5}}$Ca$_{\mathrm{0.5}}$Mn$^{\mathrm{3.5+}}$O$_{\mathrm{3}}$ [1]. Perovskite PbCoO$_{\mathrm{3}}$ synthesized at 12 GPa was found to have an unusual average charge distribution of Pb$^{\mathrm{3.5+}}$Co$^{\mathrm{2.5+}}$O$_{\mathrm{3}}$ with half-integer valences in both of A and B sites. Comprehensive studies using electron diffraction (ED), synchrotron X-ray diffraction (SXRD), neutron powder diffraction (NPD) and measurements of magnetic and electrical properties provide evidence of lead ion and cobalt ion charge ordering leading to Pb$^{\mathrm{2+}}$Pb$^{\mathrm{4+}}_{\mathrm{3}}$Co$^{\mathrm{2+}}_{\mathrm{2}}$Co$^{\mathrm{3+}}_{\mathrm{2}}$O$_{\mathrm{12}}$ quadruple perovskite structure. Here we show that half-integer valence states in both the A and B sites can be stabilized by tuning the energy levels of Pb 6$s$ and transition metal 3$d$ orbitals. [1] P. G. Radaelli et al., Phys. Rev. B \textbf{55}, 3015--3023 (1997). [Preview Abstract] |
Thursday, March 16, 2017 4:06PM - 4:18PM |
V20.00009: Probing Collective Spin Excitations in the $S = 1$ La$_2-x$Sr$_x$NiO$_4$ using X-Rays Gilberto Fabbris, D. Meyers, L. Xu, V. M. Katukuri, L. Hozoi, J. van den Brink, X. Liu, J. Okamoto, D. J. Huang, T. Schmitt, A. Uldry, B. Delley, D. Prabhakaran, A. T. Boothroyd, G. D. Gu, Mark P. M. Dean Resonant inelastic x-ray scattering (RIXS) has recently emerged as a direct probe of collective magnetic excitations (magnons) of spin $\frac{1}{2}$ materials, being particularly useful for systems that remain elusive to inelastic neutron scattering (INS), such as thin films or at ultra-fast timescales. However, the ability of RIXS to probe magnons in higher order spin systems has not been demonstrated. Here we show that Ni L$_3$-edge RIXS is sensitive to both $\Delta m_s$ = 1 and 2 magnons in the $S = 1$ La$_{2-x}$Sr$_x$NiO$_4$. We observe a doping-induced softening of magnetic interactions, which agrees with INS results, but is different from the behavior observed in cuprates. Through the RIXS sensitivity to charge and orbital excitations, we infer that the observed differences between cuprates and nickelates are related to distinct electronic character of the doped charges. The consequences of this work for study of magnetism in Ni-based heterostructures will be briefly discussed. [1] G. Fabbris et al., in prep. (2017); [2] G. Fabbris et al. PRL 117, 147401 (2016). [Preview Abstract] |
Thursday, March 16, 2017 4:18PM - 4:30PM |
V20.00010: Dimension-Reducing Quantum Transition in Copper Elpasolite Arthur Ramirez, Nicolas Blanc, Jennifer Trinh, Lianyang Dong, Xiaojian Bai, Adam Aczel, Martin Mourigal, Leon Balents, Theo Siegrist The cubic compound K$_{2}$PbCu(NO$_{2})_{6}$ (elpasolite) undergoes Jahn-Teller-driven orbital ordering near 270K, which results in quasi-1D behavior below 5K. At T$_{N} \quad =$ 0.7K, the Cu$^{2+}$ s $=$ 1/2 spins undergo Neel order, due to an inter-chain interaction approximately 10 times smaller than the intra-chain interaction of 5.4 k$_{B}$. Application of a magnetic field initially increases T$_{N}$ due to spin-dimensionality reduction. We present measurements of the specific heat, susceptibility, and neutron diffraction to characterize both the zero-field ordered state as well as the phase boundary as T approaches zero. [Preview Abstract] |
Thursday, March 16, 2017 4:30PM - 4:42PM |
V20.00011: Crystal Growth of the S$=$\textbf{1/2 Antiferromagnet K}$_{\mathrm{\mathbf{2}}}$\textbf{PbCu(NO}$_{\mathrm{\mathbf{2}}}$\textbf{)}$_{\mathrm{\mathbf{6}}}$\textbf{ Elpasolite } Lianyang Dong, Tiglet Besara, Theo Siegrist The elpasolite \textit{K2PbCu(NO2)6 }is known for its two structural transitions at 281 K and 273 K. Single crystals of \textit{K2PbCu(NO2)6 }have been grown in aqueous solution, but the rapid nucleation rate and convective transport renders it difficult to obtain large high quality single crystals. We developed a gel method to grow $K_{2}$\textit{PbCu(NO}$_{2})_{6}$ Elpasolite with sizes up to 5x5x5 mm$^{\mathrm{3}}$, suitable for neutron diffraction measurements. Susceptibility measurements clearly show that the Jahn-Teller distortions at 286K and 273K with associated orbital ordering produce a linear chain Heisenberg antiferromagnetic system. The intrachain interaction strength has been derived from a Bonner-Fisher analysis that yielded a value of 5.4K. [Preview Abstract] |
Thursday, March 16, 2017 4:42PM - 4:54PM |
V20.00012: Inelastic X-ray scattering study of incipient and realized structural transitions in mercurous halides Connor Occhialini, Ayman Said, Ahmet Alatas, Sudhir Trivedi, Jason Hancock We present new x-ray scattering investigations of mercury halides Hg$_2$X$_2$, where X=I,Br in an effort to compare lattice dynamics and structural properties of an incipient (X=I) and realized (X=Br) structural phase transition. For the realized structural transition in Hg$_2$Br$_2$, we find mode softening centered on the X point in the high-temperature body-centered tetragonal Brillouin zone in a realized transition to a lower-symmetry orthorhombic phase below $T_c\simeq$140 K. For the incipient transition in Hg$_2$I$_2$, we also find dramatic mode softening along the $\Gamma$-X direction, implying a putative transition temperature of $T_c$=-22K. In addition, we report the first temperature dependent lattice parameter development in these two systems, and compare these structural properties of the mercurous halides (Hg$_2$X$_2$) with 3$d$ transition metal trifluorides (XF$_3$), which host novel phases including negative thermal expansion. [Preview Abstract] |
Thursday, March 16, 2017 4:54PM - 5:06PM |
V20.00013: Preparation of epitaxial ScF$_{3}$ thin films Amani S. Jayakody, Zhiwei Zhang, Z. H. Zhu, Hope Whitelock, Joseph I. Budnick, Jason N. Hancock, B. O. Wells Scandium trifluoride (ScF$_{3}$) is known for a pronounced negative thermal expansion over a wide range of temperature, from 10 K to 1100 K. The structure of ScF$_{3}$ can be described as an ABX$_{3}$ perovskite with an empty A-site. Related trifluorides have a cubic-to-rhombohedral structural phase transition above room temperature. In contrast ScF$_{3}$ has a cubic structure at all temperatures below its’ high melting point, 1800 K. We have begun to grow ScF$_{3}$ films on oxide substrates using pulsed laser deposition (PLD). There are several unique features to this material that pose challenges for PLD growth: large band gap, non-oxide, poor adhesion under pressure. We have made substantial progress, producing films with a large fraction having very good epitaxy and small mosaic, but remaining regions that are polycrystalline. We update the growth status and initial characterization of ScF$_{3}$ films. [Preview Abstract] |
Thursday, March 16, 2017 5:06PM - 5:18PM |
V20.00014: Unique magnetism and structural transformation in rare earth dialumindes Arjun Pathak, Yaroslav Mudryk, Durga Paudyal, Vitalij Pecharsky Rare earth metallic alloys play a critical yet often obscure role in numerous technological applications, including but not limited to sensors, actuators, permanent magnets, and rechargeable batteries; therefore, understanding their fundamental properties is of utmost importance. We study structural behavior, specific heat, and magnetism of various binary and pseudobinary rare earth dialumindes by means of temperature-dependent x-ray powder diffraction, heat capacity and magnetization measurements, and first principles calculations. Here, we focus on our recent understanding of low temperature magnetism, and crystal structure of DyAl$_{\mathrm{2}}$, TbAl$_{\mathrm{2}}$, PrAl$_{\mathrm{2}}$, ErAl$_{\mathrm{2}}$, and discuss magnetic and structural instabilities in the pseudobinary PrAl$_{\mathrm{2}}$ -- ErAl$_{\mathrm{2}}$ system [1]. Unique among other mixed heavy lanthanide dialumindes, the substitution of Er in Pr$_{\mathrm{1-x}}$Er$_{\mathrm{x}}$Al$_{\mathrm{2}}$ results in unusual ferrimagnetic behavior, and the ferrimagnetic interactions become strongest around x $=$ 0.25. [1] A. K. Pathak et al, Phys. Rev. Lett. \textbf{110}, 186405 (2013), Phys. Rev. B \textbf{89}, 224411 (2014). [Preview Abstract] |
Thursday, March 16, 2017 5:18PM - 5:30PM |
V20.00015: Jahn-Teller distortion driven magnetic polarons in magnetite Hsiao-Yu Huang, Zhi-Yin Chen, Ru-Pang Wang, Frank M. F. de Groot, Wen-Bin Wu, Jun Okamoto, Ashish Chainani, Jianshi Zhou, Horng-Tay Jeng, Guang-Yu Guo, Je-Geun Park, Lia Huo Tjeng, Chien-Te Chen, Di-Jing Huang The first known magnetic mineral, magnetite (Fe$_{3}$O$_{4}$), has unusual properties which have fascinated mankind for centuries; it undergoes the Verwey transition at $T_{V} \sim$ 120 K with an abrupt change in structure and electrical conductivity. The mechanism of the Verwey transition however remains contentious. Here we use resonant inelastic X-ray scattering (RIXS) over a wide temperature range across the Verwey transition to identify and separate out the magnetic excitations derived from nominal Fe$^{2+}$ and Fe$^{3+}$ states. Comparison of the RIXS results with crystal-field multiplet calculations shows that the spin-orbital $dd$ excitons of the Fe$^{2+}$ sites arise from a tetragonal Jahn- Teller active polaronic distortion of the Fe$^{2+}$O$_{6}$ octahedra. These low-energy excitations, which get weakened for temperatures above 350 K but persist at least up to 550 K, are best explained as magnetic polarons. [Preview Abstract] |
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