Condensed Matter Physics Commons^™

New View Of The Occupied Band Structure Of Mo(112), Keisuke Fukutani, Hirokazu Hayashi, I. N. Yakovkin, Tula R. Paudel, Takafumi Habuchi, Daisuke Hirayama, Jian Jiang, Hideaki Iwasawa, Kenya Shimada, Ning Wu, Evgeny Y. Tsymbal, Yaroslav B. Losovyj, Peter A. Dowben

Evgeny Tsymbal Publications

We present a comprehensive examination of the occupied surface-weighted band structure of Mo(112) along the two high-symmetry directions of the surface Brillouin zone, both from theoretical and experimental perspectives. The band structures are found to be significantly different for the states along the two high-symmetry directions and for the states with even and odd reflection parities with respect to the mirror planes. The present study suggests the existence of a number of surface-weighted bands along both high-symmetry directions. The complexity of the band structure near the Fermi level may impose potential difficulties in experimental determination of the electronphonon coupling parameters …

Ferroelectric And Multiferroic Tunnel Junctions, Evgeny Y. Tsymbal, Alexei Gruverman, Vincent Garcia, Manuel Bibes, A. Barthélémy

Evgeny Tsymbal Publications

The phenomenon of electron tunneling has been known since the advent of quantum mechanics, but continues to enrich our understanding of many fields of physics, as well as creating subfields on its own. Spin-dependent tunneling in magnetic tunnel junctions has aroused considerable interest and development. In parallel with this endeavor, recent advances in thin-film ferroelectrics have demonstrated the possibility of achieving stable and switchable ferroelectric polarization in nanometer-thick films. This discovery opened the possibility of using thin-film ferroelectrics as barriers in magnetic tunnel junctions, thus merging the fields of magnetism, ferroelectricity, and spin-polarized transport into an exciting and promising area …

Magnetoelectric Interactions Between An Organic Ferroelectric And A Transition Metal Ferromagnet, Abhijit Mardana

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

The interaction between ferromagnetic and ferroelectric films, the magnetoelectric effect, is a fascinating fundamental research area as well as having potential applications in magnetic data storage devices. We have investigated magnetoelectric coupling effects in thin film heterostructures, consists of metallic ferromagnet, cobalt, and the polymer ferroelectric [P(VDF-TrFE) 70:30]. The work described here encompasses changes in ferroelectric polarization with magnetic field as well as changes in the magnetic anisotropy with ferroelectric polarization.

In samples of Co overlayers on P(VDF-TrFE), in which the Co is not constrained by the substrate, the polarization shows a large change on application of a perpendicular magnetic …

Qpced2.0: A Computer Program For The Processing And Quantification Of Polycrystalline Electron Diffraction Patterns, Xingzhong Li

Nebraska Center for Materials and Nanoscience: Faculty Publications

The processing and quantification of electron diffraction patterns have become vital in advanced electron crystallographic analysis work. A computer program, QPCED2.0, has been developed for the handling of selected-area electron diffraction patterns for polycrystalline materials. QPCED2.0 can be used to enhance the visibility of electron diffraction patterns, to convert electron diffraction patterns into intensity profiles, and to retrieve precisely the lattice d spacings and the integral intensities of the diffraction rings. The design and implementation of QPCED2.0 are elucidated and application examples are given.

Magnetic And Superconducting Phases At The Laalo3/Srtio3 Interface: The Role Of Interfacial Ti 3D Electrons, N. Pavlenko, Thilo Kopp, Evgeny Y. Tsymbal, George A. Sawatzky, Jochen Mannhart

Evgeny Tsymbal Publications

Ferromagnetism and superconductivity are, in most cases, adverse. However, recent experiments reveal that they coexist at interfaces of LaAlO₃ and SrTiO₃. We analyze the magnetic state within density functional theory and provide evidence that magnetism is not an intrinsic property of the two-dimensional electron liquid at the interface. We demonstrate that the robust ferromagnetic state is induced by the oxygen vacancies in SrTiO₃ or in the LaAlO₃ layer. This allows for the notion that areas with increased density of oxygen vacancies produce ferromagnetic puddles and account for the previous observation of a superparamagnetic behavior in …

Multiferroic Tunnel Junctions With Poly(Vinylidene Fluoride), Julian P. Velev, Juan M. López-Encarnación, John D. Burton, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

We perform first-principles calculations based on density functional theory of the spin-resolved conductance of poly(vinylidene fluoride)- (PVDF) based multiferroic tunnel junctions (MFTJs).We consider Co/PVDF/O/Co (0001) MFTJs with one oxidized interface, representing the different experimental growth conditions for the two interfaces. We demonstrate that this natural asymmetry leads to multiple resistance states associated with different magnetization configurations of the electrodes and ferroelectric polarization orientations of the barrier. Our results indicate very high tunability of the tunneling magnetoresistance and electroresistance effects, which could be useful for logic and memory applications.

Interface Dipole Effect On Thin Film Ferroelectric Stability: First-Principles And Phenomenological Modeling, Xiaohui Liu, Yong Wang, Pavel V. Lukashev, John D. Burton, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Utilization of the switchable spontaneous polarization of ferroelectric materials offers a promising avenue for the future of nanoelectronic memories and logic devices provided that nanoscale metal-ferroelectric-metal heterostructures can be engineered to maintain a bi-stable polarization switchable by an applied electric field. The most challenging aspect of this approach is to overcome the deleterious interface effects which tend to render ferroelectric polarization either unstable or unswitchable and which become ever more important as ferroelectric materials are produced thinner and thinner. Here we use first-principles density functional calculations and phenomenological modeling to demonstrate that a BaO/RuO₂ interface termination sequence in SrRuO …

Coherent Potential Approximation As A Voltage Probe, Mikhail Ye. Zhuravlev, A. V. Vedyayev, Kirill D. Belashchenko, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Coherent potential approximation (CPA) haswidely been used for studying the residual resistivity of bulk alloys and electrical conductivity in systems with structural disorder. Here, we revisit the single-site CPA within the Landauer-Büttiker approach applied to the electronic transport in layered structures and show that thismethod can be interpreted in terms of the B¨uttiker voltage-probe model that has been developed for treating phase-breaking scattering in mesoscopic systems. We demonstrate that the on-site vertex function, which appears within the single-site CPA formalism, plays the role of the local chemical potential within the voltage-probe approach. This interpretation allows the determination of the chemical …

Intrinsic Defects In Multiferroic Bifeo3 And Their Effect On Magnetism, Tula R. Paudel, Sitaram S. Jaswal, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

We investigate the energetics of the intrinsic defects in bulk multiferroic BiFeO₃ and explore their implication for magnetization using a first-principles approach based on density functional theory. We find that the dominant defects in oxidizing (oxygen-rich) conditions are Bi and Fe vacancies and in reducing (oxygen-poor) conditions are O and Bi vacancies. The calculated carrier concentration shows that the BiFeO₃ grown in oxidizing conditions has p-type conductivity. The conductivity decreases with oxygen partial pressure, and the material becomes insulating with a tendency for n-type conductivity. We find that the Bi and Fe vacancies produce a magnetic …

Growth Diagram And Magnetic Properties Of Hexagonal Lufe2o4 Thin Films, Wenbin Wang, Zheng Gai, Miaofang Chi, Jason D. Fowlkes, Jieyu Yi, Leyi Zhu, Xuemei Cheng, David J. Keavney, Paul C. Snijders, Thomas Z. Ward, Jian Shen, Xiaoshan Xu

Xiaoshan Xu Papers

Agrowth diagram of Lu-Fe-O compounds on MgO (111) substrates using pulsed laser deposition is constructed based on extensive growth experiments. The LuFe₂O₄ phase can only be grown in a small range of temperature and O₂ pressure conditions. An understanding of the growth mechanism of Lu-Fe-O compound films is offered in terms of the thermochemistry at the surface. Superparamagnetism is observed in the LuFe₂O₄ film and is explained in terms of the effect of the impurity hexagonal LuFeO₃ (h-LuFeO₃) phase and structural defects.

Crystal Field Splitting And Optical Bandgap Of Hexagonal Lufeo3 Films, Wenbin Wang, Hongwei Wang, Xiaoying Xu, Leyi Zhu, Lixin He, Elizabeth Wills, Xuemei Cheng, David J. Keavney, Jian Shen, Xifan Wu, Xiaoshan Xu

Xiaoshan Xu Papers

Hexagonal LuFeO₃ films have been studied using x-ray absorption and optical spectroscopy. The crystal splitting of Fe³⁺ is extracted as E_e' - E_e" = 0.7 eV and E_a'1 - E_e' = 0.9 eV, and a 2.0 eV optical bandgap is determined assuming a direct gap. First-principles calculations confirm the experiments that the relative energies of crystal field splitting states do follow E_a'1 > E_e' > E_e" with slightly underestimated values and a bandgap of 1.35 eV.

Understanding The Effect Of Ferroelectric Polarization On Power Conversion Efficiency Of Organic Photovoltaic Devices, Yongbo Yuan, Pankaj Sharma, Zhengguo Xiao, Shashi Poddar, Alexei Gruverman, Stephen Ducharme, Jinsong Huang

Stephen Ducharme Publications

It is demonstrated that the power conversion efficiency (PCE) of organic photovoltaic devices can be increased by inserting an ultrathin film of a ferroelectric co-polymer, poly(vinylidenefluoridetrifluoroethylene) (P(VDF-TrFE)), at the metal–organic interface, due to an enhancement of the charge extraction efficiency. Specifically, the effect of P(VDF-TrFE) crystallinity on its function in ferroelectric organic photovoltaic (FE-OPV) devices has been studied by several methods. Highly crystalline and amorphous P(VDF-TrFE) films have been prepared by the Langmuir–Blodgett method and spincoating from acetone solution, respectively. The polymer solar cell devices with a crystalline P(VDFTrFE) interfacial layer at the cathode have larger PCE than the structures …

Ferroelectric Control Of Magnetocrystalline Anisotropy At Cobalt/Poly(Vinylidene Fluoride) Interfaces, Pavel Lukashev, Tula R. Paudel, Juan M. López-Encarnación, Shireen Adenwalla, Evgeny Y. Tsymbal, Julian P. Velev

Shireen Adenwalla Papers

Electric field control of magnetization is one of the promising avenues for achieving high-density energy-efficient magnetic data storage. Ferroelectric materials can be especially useful for that purpose as a source of very large switchable electric fields when interfaced with a ferromagnet. Organic ferroelectrics, such as poly(vinylidene fluoride) (PVDF), have an additional advantage of being weakly bonded to the ferromagnet, thus minimizing undesirable effects such as interface chemical modification and/or strain coupling. In this work we use first-principles density functional calculations of Co/PVDF heterostructures to demonstrate the effect of ferroelectric polarization of PVDF on the interface magnetocrystalline anisotropy that controls the …

Two-Dimensional Electron Gas At Oxide Interfaces, Karolina Janicka

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

Extraordinary phenomena can occur at the interface between two oxide materials. A spectacular example is a formation of a two-dimensional electron gas (2DEG) at the SrTiO₃/LaAlO₃ interface. In this dissertation the properties of the 2DEG are investigated from first principles.

The spatial extent of the 2DEG formed at the SrTiO₃/LaAlO₃ n-type interface is studied. It is shown that the confinement of the 2DEG is controlled by metal induced gap states formed in the band gap of SrTiO₃. The confinement width is then determined by the attenuation length of the metal induced gap …

First-Principles Studies On Physical And Chemical Properties Of Nanostructures, Menghao Wu

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

The physical and chemical properties of decorated graphene and graphene ribbons, single-layer III-V systems, three-dimensional carbon and BN foam, and transition-metal-molecular sandwich nanowires have been investigated by first-principle calculations and their potential applications have been predicted. First, it is shown that zigzag graphene nanoribbons (ZGNRs) can be converted into half metal when their edges are decorated by some chemical functional groups, and the half-metalicity is induced by chemical potential difference between two edges when one edge is decorated by electron-donating group like –OH and the other edge is decorated by electron-accepting group like –F, -NH₂, -N(CH₃) …

Thermodynamics Of Magnetic Multilayers, Tathagata Mukherjee

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

Our interest in thermodynamics of magnetic thin film heterostructure began by exploring the possibility to use magnetic nanostructures in the search for optimized magnetocaloric materials for potential room temperature refrigeration. In the present thesis magnetic thin film heterostructures are experimentally realized by Molecular Beam Epitaxy (MBE) and Pulsed Laser Deposition (PLD). Co/Cr and Fe/Cr superlattices were fabricated using mean-field theoretical concepts as guiding principles. The potential of artificial antiferromagnets for near room-temperature refrigeration is explored. Magnetocaloric properties are deduced from measurements of the temperature and field dependence of the magnetization of our samples. The effects of intra-plane and inter-plane exchange …

Self Assembly And Interface Chemistry Of Non-Metallated Tetraphenyl Porphyrin, Geoffrey Rojas

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

The study of the electronic properties and geometrical arrangement of 5, 10, 15, 20-tetraphenyl-21H, 23H-porphine on metal is presented. The systems were analyzed using both scanning tunneling microscopy and photoelectron spectroscopy and compared across surfaces to determine how the interface chemistry between the metal and molecule affect the self-assembly and band structure of the adsorbed species. The molecules are found to self-assemble and grow on the Ag(111) surface in a manner described by similar models to weakly bound metal/metal surface systems. The CH-pi bonds between molecules are found to largely determine the relative inter-molecular arrangement, while the more isotropic van …

Functional Two-Dimensional Electronic Gases At Interfaces Of Oxide Heterostructures, Yong Wang

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

A quasi-two dimensional electron gas (2DEG) in oxide heterostructures such as LaAlO₃/SrTiO₃ has unique properties that are promising for applications in all-oxide electronic devices. In this dissertation, we focus on understanding and predicting novel properties of the 2DEG by performing first-principles electronic calculations within the frame work of density-functional theory (DFT).

The effects of polarization in all-oxide heterostructures incorporating different ferroelectric constituents, such as KNbO₃/ATiO₃ (A = Sr, Ba, Pb), are investigated. It is found that screening charge at the interface that counteracts the depolarizing electric field in the ferroelectric material significantly changes the …

Domain Size And Structure In Exchange Coupled [Co/Pt]/Nio/[Co/Pt] Multilayers, Andrew G. Baruth, Shireen Adenwalla

Shireen Adenwalla Papers

We investigate the competing effects of interlayer exchange coupling and magnetostatic coupling in the magnetic heterostructure ([Co/Pt]/NiO/[Co/Pt]) with perpendicular magnetic anisotropy (PMA). This particular heterostructure is unique among coupled materials with PMA in directly exhibiting both ferromagnetic and antiferromagnetic coupling, oscillating between the two as a function of spacer layer thickness. By systematically tuning the coupling interactions via a wedge-shaped NiO spacer layer, we explore the energetics that dictate magnetic domain formation using high resolution magnetic force microscopy coupled with the magneto-optical Kerr effect. This technique probes the microscopic and macroscopic magnetic behavior as a continuous function of thickness and …

The Interplay Between Symmetry And Static Dipoles With Adsorption On Molecular Substrates, Zhengzheng Zhang

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

This thesis presents evidence of preferential adsorption and the associated dipole-dipole interactions that can occur at molecule to molecule interfaces. The results are discussed in the context of the possibility of interactions caused by strong intrinsic dipoles when adsorbed on electrostatically biased substrates. Key is the discovery of lock and key adsorption chemistry by comparing the reversible absorption of the three isomers of di-iodobenzene (1,2-di-iodobenzene, 1,3-di-iodobenzene, and 1,4-di-iodobenzene) on molecular films of a quinonoid zwitterion. There is unequivocal evidence that the molecular adsorption and absorption of 1, 3-diiodobenzene is strongly favored at 150 K over the other isomers of di-iodobenzene. …

The Photofragmentation Processes Of The Closo-Carborane And The Local Structure Of Transition Metal Doped Semiconducting Boron Carbide Thin Films, Jing Liu

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

I investigated the photofragmentation processes of various closo-carboranes in an effort to understand the radical-induced polymerization of the closo-carboranes (i.e., semiconducting film growth), based on their partial dehydrogenation during plasma-enhanced chemical vapor deposition. The chemistry of vacuum ultraviolet VUV assisted dehydrogenation processes of both the closo-carboranes and related closo-phosphacarboranes were compared by photoionization mass spectrometry studies. The dominant ion pairs were identified and compared with the energetics constructed by theoretical modeling for the possible dissociation pathways.

Transition metal (Mn, Fe, Co) doped boron carbides thin films produced by plasma-enhanced chemical vapor deposition of orthocarborane (closo …

Highly Spin-Polarized Conducting State At The Interface Between Nonmagnetic Band Insulators: Laalo3/Fes2 (001), John D. Burton, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

First-principles density functional calculations demonstrate that a spin-polarized two-dimensional conducting state can be realized at the interface between two nonmagnetic band insulators. The (001) surface of the diamagnetic insulator FeS₂ (pyrite) supports a localized surface state deriving from Fe d orbitals near the conduction band minimum. The deposition of a few unit cells of the polar perovskite oxide LaAlO₃ leads to electron transfer into these surface bands, thereby creating a conducting interface. The occupation of these narrow bands leads to an exchange splitting between the spin subbands, yielding a highly spin-polarized conducting state distinct from the rest of …

Tailoring A Two-Dimensional Electron Gas At The Laalo3 ∕ Srtio3 (001) Interface By Epitaxial Strain, C. W. Bark, D. A. Felker, Yong Wang, H. W. Jang, C. M. Folkman, J. W. Park, S. H. Baek, H. Zhou, D. D. Fong, X. Q. Pan, Evgeny Y. Tsymbal, M. S. Rzchowski, Chang-Beom Eom

Evgeny Tsymbal Publications

Recently a metallic state was discovered at the interface between insulating oxides, most notably LaAlO₃ and SrTiO₃. Properties of this two-dimensional electron gas (2DEG) have attracted significant interest due to its potential applications in nanoelectronics. Control over this carrier density and mobility of the 2DEG is essential for applications of these unique systems, and may be achieved by epitaxial strain. However, despite the rich nature of strain effects on oxide materials properties, such as ferroelectricity, magnetism, and superconductivity, the relationship between the strain and electrical properties of the 2DEG at the LaAlO₃∕SrTiO₃ heterointerface remains …

Schottky Barrier Formation At The Au To Rare Earth Doped Gan Thin Film Interface, S. R. Mchale, J. W. Mcclory, J. C. Petrosky, J. Wu, R. Palai, Yaroslav B. Losovyj, Peter A. Dowben

Peter Dowben Publications

The Schottky barriers formed at the interface between gold and various rare earth doped GaN thin films (RE = Yb, Er, Gd) were investigated in situ using synchrotron photoemission spectroscopy. The resultant Schottky barrier heights were measured as 1.68 ± 0.1 eV (Yb:GaN), 1.64 ± 0.1 eV (Er:GaN), and 1.33 ± 0.1 eV (Gd:GaN). We find compelling evidence that thin layers of gold do not wet and uniformly cover the GaN surface, even with rare earth doping of the GaN. Furthermore, the trend of the Schottky barrier heights follows the trend of the rare earth metal work function.

Structure And Magnetism Of Mnau Nanoclusters, X. Wei, Damien Le Roy, Ralph Skomski, Xingzhong Li, Zhiguang Sun, Jeffrey E. Shield, M. J. Kramer, David J. Sellmyer

Nebraska Center for Materials and Nanoscience: Faculty Publications

Equiatomic MnAu clusters with average sizes of 4 and 10 nm are produced by inert-gas condensation. As-produced clusters are used to form both dense cluster films and films with clusters embedded in a W matrix with a cluster volume fraction of 25%. Both structure and magnetism are size-dependent. Structural analysis of the 10 nm clusters indicate a distorted tetragonal body-centered cubic structure with lattice parameters a=0.315 and c=0.329 nm. The 4 nm clusters have a partially ordered tetragonal L10 structure with lattice parameters a=0.410 nm and c=0.395 nm. Magnetic properties of the clusters show evidence at …

Magnetism Of Cluster-Deposited Y–Co Nanoparticles, Balamuruga Balamurugan, Ralph Skomski, Xingzhong Li, V. R. Shah, George C. Hadjipanayis, Jeffrey E. Shield, David J. Sellmyer

Nebraska Center for Materials and Nanoscience: Faculty Publications

Nanoparticles of YCo₂, YCo_3, and YCo₅ are produced by cluster-deposition and investigated both structurally and magnetically. The nanoparticles have sizes of less than 10 nm and are superparamagnetic at 300 K, irrespective of stoichiometry. As-produced nanoparticles exhibit disordered structures with magnetic properties differing from those of the bulk particles. The temperature-dependent magnetization curves of the nanoparticles reveal blocking temperatures from 110 to 250 K, depending on stoichiometry. The magnetic anisotropy constant K₁ of disordered YCo₅ nanoparticles of 7.8 nm in size is 3.5×10⁶ergs/cm³, higher than those of the disordered YCo …

Metastability Of Free Cobalt And Iron Clusters: A Possible Precursor To Bulk Ferromagnetism, Xiaoshan Xu, Shuangye Yin, Ramiro Moro, Anthony Liang, John Bowlan, Walt A. De Heer

Xiaoshan Xu Papers

Homonuclear cobalt and iron clusters Co_N and Fe_N measured in a cryogenic molecular beam exist in two states with distinct magnetic moments (μ), polarizabilities, and ionization potentials, indicating distinct valences. The μ is approximately quantized: μ_N ~ 2Nμ_B in the ground states and μ_N* ~ Nμ_B in the excited states for Co; μ_N ~ 3N μ_B and μ_N * ~ Nμ_B for Fe. At a large size, the average μ of the two states converges to the bulk value with diminishing ionization potential differences. …

Mesoscale Flux-Closure Domain Formation In Single-Crystal Batio3, R. G.P. Mcquaid, L. J. Mcgilly, Pankaj Sharma, Alexei Gruverman, J. M. Gregg

Alexei Gruverman Publications

Over 60 years ago, Charles Kittel predicted that quadrant domains should spontaneously form in small ferromagnetic platelets. He expected that the direction of magnetization within each quadrant should lie parallel to the platelet surface, minimizing demagnetizing fields, and that magnetic moments should be configured into an overall closed loop, or flux-closure arrangement. Although now a ubiquitous observation in ferromagnets, obvious flux-closure patterns have been somewhat elusive in ferroelectric materials. This is despite the analogous behaviour between these two ferroic subgroups and the recent prediction of dipole closure states by atomistic simulations research. Here we show Piezoresponse Force Microscopy images of …

Metallic And Insulating Oxide Interfaces Controlled By Electronic Correlations, H. W. Jang, D. A. Felker, C. W. Bark, Y. Wang, Manish K. Niranjan, C. T. Nelson, Y. Zhang, D. Su, C. M. Folkman, S. H. Baek, S. Lee, K. Janicka, Y. Zhu, X. Q. Pan, D. D. Fong, Evgeny Y. Tsymbal, M. S. Rzchowski, Chang-Beom Eom

Evgeny Tsymbal Publications

The formation of two-dimensional electron gases (2DEGs) at complex oxide interfaces is directly influenced by the oxide electronic properties. We investigated how local electron correlations control the 2DEG by inserting a single atomic layer of a rare-earth oxide (RO) [(R is lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), or yttrium (Y)] into an epitaxial strontium titanate oxide (SrTiO₃) matrix using pulsed-laser deposition with atomic layer control. We find that structures with La, Pr, and Nd ions result in conducting 2DEGs at the inserted layer, whereas the structures with Sm or Y ions are insulating. Our local …

Transport Spin Polarization Of High-Curie Temperature Mnbi Films, Parashu Kharel, P. Thapa, Pavel V. Lukashev, Renat F. Sabirianov, Evgeny Y. Tsymbal, D. J. Sellmyer, Boris Nadgorny

Evgeny Tsymbal Publications

We report on the study of the structural, magnetic, and transport properties of highly textured MnBi films with the Curie temperature of 628 K. In addition to detailed measurements of resistivity and magnetization, we measure transport spin polarization of MnBi by Andreev reflection spectroscopy and perform fully relativistic band-structure calculations of MnBi. A spin polarization from 51% ± 1% to 63% ± 1% is observed, consistent with the calculations and with an observation of a large magnetoresistance in MnBi contacts. The band-structure calculations indicate that in spite of almost identical densities of states at the Fermi energy, the large disparity …