Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session J49: Metals: Magnetic and Structural 
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Sponsoring Units: DMP Chair: Hans Boschker, Max Planck Institute for Solid State Research Room: Mile High Ballroom 1B 
Tuesday, March 3, 2020 2:30PM  2:42PM 
J49.00001: Coulomb correlation in noncollinear antiferromagnetic αMn Aki Pulkkinen, Bernardo Barbiellini, Johannes Samuli Nokelainen, Vladimir Sokolovskiy, Danil Baigutlin, Olga Miroshkina, Mikhail Zagrebin, Vasiliy Buchelnikov, Christopher Lane, Robert Markiewicz, Arun Bansil, Jianwei Sun, Katariina Pussi, Erkki Lahderanta We discuss the interplay between magnetic and structural degrees of freedom in elemental Mn. The equilibrium volume is shown to depend critically on the magnetic interactions between the Mn atoms. While the standard generalizedgradientapproximation underestimates the equilibrium volume, a more accurate treatment of the effects of electronic localization and magnetism is found to solve this longstanding problem. Our calculations reveal the presence of a magnetic phase in strained αMn that has been reported previously in experiments. This new phase of strained αMn is found to exhibit a noncollinear spin structure with large magnetic moments. 
Tuesday, March 3, 2020 2:42PM  2:54PM 
J49.00002: Magnetic and electronic properties of tetragonal GeNFe3 Mari Tsumuraya, David Singh GeNFe3 has a tetragonal symmetry at room temperature with a space group I4/mcm. Previous studies unveiled its physical properties, such as a spinglass behavior and anomalous Hall effect. Through firstprinciples calculations, we report magnetic and electronic properties of GeNFe3 with tetragonal structure. 
Tuesday, March 3, 2020 2:54PM  3:06PM 
J49.00003: The effect of Si substitution on the magnetocaloric properties of Al_{1.2x}Si_{x}Fe_{2}B_{2} intermetallic system Md Sakhawat Hossain Himel, Mahmud Khan The AlFe_{2}B_{2} material has drawn considerable attention recently due to its magnetocaloric properties near room temperature. Here, we have investigated the magnetic and magnetocaloric properties of a series of Sidoped Al_{1.2x}Si_{x}Fe_{2}B_{2 }(0 ≤ x ≤ 0.25) compounds by xray diffraction, scanning electron microscopy (SEM), and dc magnetization measurements. The samples were prepared by arcmelting followed by dropcasting and annealing. The xray diffraction patterns confirmed that all samples exhibited the singlephase Cmmmtype orthorhombic crystal structure. SEM micrographs confirmed the homogeneity of the samples. A secondorder ferromagnetic phase transition was observed near room temperature for all samples. While the Curie temperature (Tc) was minutely effected due to Si doping, the magnetocaloric properties were significantly enhanced. A peak magnetic entropy change of 7.39 Jkg^{1}K^{1} was observed in the doped samples for a field change of 50 kOe. The experimental results and related discussion will be presented in detail. 
Tuesday, March 3, 2020 3:06PM  3:18PM 
J49.00004: A firstprinciples study of the impact of paramagnetism on grain boundary segregation in FeMn alloys Omkar Gopalkrishna Hegde, Tilmann Hickel, Christoph Freysoldt, Joerg Neugebauer To understand the impact of paramagnetism on defect energetics and kinetics is, though conceptually and computationally challenging, important for designing Febased alloys. Since magnetic degrees of freedom change faster than atomic degrees of freedom in the hightemperature paramagnetic state, the atoms move according to an averaged force instead of instantaneous forces attained from each spin configuration. 
Tuesday, March 3, 2020 3:18PM  3:30PM 
J49.00005: Tuning of the collapsed tetragonal phase transition in the SrTM_{2}P_{2} (TM = transition metal) system Guilherme Gorgen Lesseux, Raquel Ribeiro, Sergey L. Bud'ko, Paul C Canfield The tetragonal to collapsed tetragonal phase transition^{1} combines dramatic changes in structural, electronic, and (sometimes) magnetic states. This phase transformation can be controlled by application of hydrostatic pressure or uniaxial stress and offers the possibility of achieving shape memory behavior combined with remarkable superelastic properties in intermetallic compounds.^{2} For the SrTM_{2}P_{2} system, given that the collapse occurs when PP bonding takes place across Sr plane, TM substitution is the least perturbative substitution that can be made. As part of our effort to broaden our understanding and control of this transition, we have studied the effects of transition metal substitution on SrNi_{2}P_{2}. Here we report on solution growth and transport measurements on single crystals of SrTM_{2}P_{2} (TM = Ni, Rh, Pd, Cu) which are potential hosts for the tetragonal collapse transition. Particularly, the effects of Rhdoping on SrNi_{2}P_{2} will be discussed. 
Tuesday, March 3, 2020 3:30PM  3:42PM 
J49.00006: First Principles study of enhanced stability of Au@Pt nanoparticles on MoS_{2} support through alloying kinetics Timothy T Yang, Boao Song, Wissam A Saidi, Reza ShahbazianYassar Twodimensional MoS_{2} supported Pt and Au@Pt nanoparticles (NPs) have received great attention for various catalysis applications. Deep understanding on the NPs migration and coalescence under different service conditions is crucial to enhance their stability. Herein, we employ firstprinciples density functional theory calculations to study the stabilities and diffusion kinetics of supported Au@Pt NPs at room temperature up to 400 °C in atmospheric hydrogen and vacuum environments. We show that Pt at the bottom layer of the NP interacts strongly with the MoS_{2} substrate resulting in a strong adhesion energy. However, the adhesion energy is reduced in hydrogen environment due to strong PtH interactions. Further, we show that smaller NPs are more favored in alloy form rather than core/shell due to the facile diffusion kinetics at the edges. Our results are validated using transmission electron microscopy, showing that small size Au@Pt alloy NPs are more stable than the larger ones with the Au core in contact with MoS_{2} substrate and Pt shell in contact with hydrogen. The present work gives insights to the degradation mechanisms of the NPs supported on substrates and offers strategies to enhance their stability. 
Tuesday, March 3, 2020 3:42PM  3:54PM 
J49.00007: Quantum Quench and fSum Rules on Linear and Nonlinear Conductivities Haruki Watanabe, Masaki Oshikawa Electric conductivity is one of the most important response properties of materials. The "frequency sum rule" is a nonperturbative constraint on the conductivity integrated over all frequency. In this talk, we give a new derivation to the fsum rule for general quantum manyparticle systems by considering a quench process. We then extend the discussion to higher order responses and derive various types of new sum rules on nonlinear conductivities. 
Tuesday, March 3, 2020 3:54PM  4:06PM 
J49.00008: Binary and ternary metallic compounds with soft magnetic properties: predictions from density functional theory calculations Akansha Singh, Aaron P. Stebner, Cristian Ciobanu Nanocrystalline magnetic materials have fundamental and technological importance, due to their soft magnetic properties. These materials have a twophase microstructure, a nanocrystalline ferromagnetic phase with D0_{3} structure and a residual amorphous alloy phase. FINEMET (Fe_{73.5}Si_{13.5}Nb_{3}B_{9}Cu_{1, }with the nanocrystalline phase Fe_{3}Si) is one such material, having large saturation magnetization, low magnetocrystalline anisotropy, and coercivity. Still, it has some disadvantages related to its brittleness and power dissipation. With the aim of finding better soft magnetic alloys, we performed a systematic computational search across binary (D0_{3}, formula X_{3}Z) and ternary (L_{21}, XY_{2}Z) compounds, using generalized gradient approximation calculations. We choose the 3dtransition metals (Sc, Ti, V, Cr, Mn, Fe, Co and Ni) as X or Y element, and Al, Si, P, Ga, Ge, As, In, Sn and Sb as Z, for a total of 576 alloy combinations. We have filtered the best candidates based on their magnetization, crystalline anisotropy, heat of formation, and ductility. We have thus found 12 compounds (including, e.g., Fe_{3}Sn, Fe_{3}Ga, Fe_{3}Sb, MnCo_{2}As) that can have properties superior to Fe_{3}Si. Our results may offer guidance for future synthesis efforts aimed at discovering new and superior soft magnetic materials 
Tuesday, March 3, 2020 4:06PM  4:18PM 
J49.00009: Ab initio thermodynamics of carbides in high Mn steels Lekshmi Sreekala, Poulumi Dey, Tilmann Hickel, Joerg Neugebauer The addition of Cr to highMn steels improves their corrosion resistance. At the same time, it has been experimentally reported that the alloying with Cr yields a substantial increase in the number of carbides, like cementite and Fe_{23}C_{6}. They can contribute to a precipitation hardening of the material, but also provide interfaces that might be critical for hydrogen embrittlement. In the present work, we therefore use density functional theory to determine the thermodynamic driving force for the formation of carbides as a function of the chemical composition of the alloy. These investigations are performed at finite temperatures considering the vibrational, electronic and magnetic contributions to the free energy of formation. We analyze the critical role of Cr by determining the partitioning of Cr and Mn into the carbides. At the same time, the role of these alloying elements for the solution enthalpy of H in the carbides is determined. We report that the chemical trends for the carbides show surprising differences from the behavior in the FeMn matrix. 
Tuesday, March 3, 2020 4:18PM  4:30PM 
J49.00010: Atomiclevel defect formation mechanism in highentropy alloys ChiHuan Tung, GuanRong Huang, WeiRen Chen, ShouYi Chang

Tuesday, March 3, 2020 4:30PM  4:42PM 
J49.00011: Drag viscosity of metals and its connection to Coulomb drag Yunxiang Liao, Victor Galitski Shear viscosity is a key parameter in the hydrodynamic description of fluids, including electronic matter  an interdisciplinary subject that has attracted an increasing amount of interest recently. Related to the rate of momentum transport, viscosity is given by the retarded correlation function of the momentum current, i.e., the stress tensor, in the linear response theory. In this work, we find that there exists a previously overlooked contribution to viscosity, which originate from the interacting part of the stress tensor. This new contribution, which we name drag viscosity, is connected to the frictional drag forces induced by the longrange interactions. A related phenomenon is the Coulomb drag of a doublelayers electronic system, which measures the rate of charge transport originating from scattering between quasiparticles in different layers in the presence of Coulomb interactions. Using the diagrammatic approach in the Keldysh formalism, we derive the drag viscosity of the 2D and 3D electronic systems as well as the drag resistivity of the 2D doublelayers systems. At low enough temperatures, both the drag viscosity and resistivity exhibit quadratic temperature dependence which becomes linear as temperature increases. 
Tuesday, March 3, 2020 4:42PM  4:54PM 
J49.00012: Local structure analysis of carbon in ferritic steel by C Kedge Xray absorption fine structure and multiple scattering calculations Kakeru Ninomiya, Yusuke Tamenori, Kazuki Tsuruta, Maiko Nishibori The ferritic steel with supersaturated solid solution carbon remarkable increase in hardness by heat treatment (socalled aging) at low temperature. This has been considered to cause by the formation of the carbon cluster in ferritic steel.^{1} In this study, we aimed to understand the local structure changes of solid solution carbon in ferritic steel with aging by soft Xray absorption spectroscopy. In the C Kedge Xray absorption near edge structure (XANES) spectrum, extended Xray absorption fine structure (EXAFS) analysis by peak fitting is difficult due to parameter restrictions based on the sampling theorem. Therefore, we proposed the analysis method of CFe bond length ratio based on Natoli's law.^{2} Because solid solution carbon in bccFe is a D_{4h} point group symmetry, it is expected that the peak position of CFe σ* state splits in the xy and z directions. We found that the CFe bond length ratio, l_{xy}/l_{z}, began to decrease with the formation of carbon clusters. Therefore, it suggests that the CFez bond was expanded by the increase of local carbon concentration due to the formation of carbon clusters, and structure transition of bcc to bct occurred. 
Tuesday, March 3, 2020 4:54PM  5:06PM 
J49.00013: Accelerating Materials Discovery through Bezier Interpolation of Electronic Band Structure Nathan Foulk, Jeremy Jorgensen, Gus Hart One important part of DFT calculations is the numerical integral of the electronic band structure. Unfortunately, this critical step of DFT simulation is the most computationally expensive, because each kpoint requires solving the KohnSham equations, an eigenproblem, in a large basis set. Almost all of the error in the band energy integral comes from misrepresenting the Fermi surface, so the most important part of any integration technique is approximating the Fermi surface correctly. Current DFT codes approximate the bands using threedimensional Riemann sums, which represent the Fermi surface very poorly. We present an integration technique of interpolating the bands using Bezier surfaces in order to more accurately represent the Fermi surface, and thereby achieve the same accuracy with fewer kpoints. We also explore further improvement by using an adaptive mesh refinement technique in those integration regions which contain the Fermi surface. Preliminary results suggest that 1 meV accuracy can be achieved using ~10× fewer kpoints. 
Tuesday, March 3, 2020 5:06PM  5:18PM 
J49.00014: Exploring band topology of engineered materials using deep neural networks Vittorio Peano, Florian Sapper, Florian Marquardt This talk focuses on the first applications of our deep Neural Network (NN) based approach to band structure calculations. A distinctive feature of our approach is that our NN does not predict the band structure directly but rather learns to predict the parameters of an auxiliary TightBinding (TB) model. This TB model gives then access not only to the band structure but also to the topological properties of the Bloch waves. 
Tuesday, March 3, 2020 5:18PM  5:30PM 
J49.00015: MicroStructure and Transport Mechanism in Graphene Copper Composites Raju Ghimire The addition of nanocarbons to copper (Cu), specifically in the form of graphene (GN), has shown to enhance copper’s physical properties. GNCu nanocomposites can potentially achieve a higher current carrying capacity and a lower temperaturesensitivity of electrical resistivity compared with copper. These characteristics make GNCu materials interesting for several applications including but not limited to interconnects, high current power lines, and elevatedtemperature rotating machines. Charge conduction in these materials is controlled by microstructural features as well as nanoscale interfacial phenomena between the GN and Cu. In this work, we analytically investigated the possibilities for an improved electrical conductivity in GNCu composites. Subsequently, GNCu samples were prepared by the consolidation of CVD Cugraphene films under high pressures and temperatures. The effects of processing time, temperature, and pressure on both the structure and physical properties of the GNCu composite films were investigated. Finally, insitu conductivity measurements of the CuGN interfaces were carried out. These measurements provide insights into transport mechanisms in nanocarbonmetal composites. 
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