Marsh, David. J., Kin Chung Fong, Erik W. Lentz, Libor ¦mejkal, Mazhar N. Ali
abstractAntiferromagnetically doped topological insulators (ATI) are among the candidates to host dynamical axion fields and axion polaritons, weakly interacting quasiparticles that are analogous to the dark axion, a long sought after candidate dark matter particle. Here we demonstrate that using the axion quasiparticle antiferromagnetic resonance in ATIs in conjunction with low-noise methods of detecting THz photons presents a viable route to detect axion dark matter with a mass of 0.7 to 3.5 meV, a range currently inaccessible to other dark matter detection experiments and proposals. The benefits of this method at high frequency are the tunability of the resonance with applied magnetic field, and the use of ATI samples with volumes much larger than 1
Parkin, S. S. P.
In: Metallic spintronics, Spintronics handbook : spin transport and magnetism ; volume 1, pp VII-X (Eds.) Tsymbal, Evgeny Y. and Zutic, Igor,CRC Press, Boca Raton 2019
Parkin, S. S. P.
In: Semiconductor spintronics, Spintronics handbook : spin transport and magnetism ; volume 2, pp VII-X (Eds.) Tsymbal, Evgeny Y. and Zutic, Igor,CRC Press, Boca Raton 2019
Parkin, S. S. P.
In: Nanoscale spintronics and applications, Spintronics handbook : spin transport and magnetism ; volume 3, pp VII-X (Eds.) Tsymbal, Evgeny Y. and Zutic, Igor,CRC Press, Boca Raton 2019
Emerging spintronic memories
Parkin, S. S. P. and Masamitsu Hayashi, Luc Thomas, Xin Jiang, Rai Moriya, William Gallagher
In: Nanoscale spintronics and applications, Spintronics handbook : spin transport and magnetism ; volume 3, pp 43-470 (Eds.) Tsymbal, Evgeny Y. and Zutic, Igor,CRC Press, Boca Raton 2019
abstractSpintronic memories are emerging as one of the next generation storage technologies to replace hard disk drives and current solid state memories. This chapter reviews the underlying physics, and the state of the technology of these emerging spintronic memories. Most conventional solid state memories require one or more transistors or switches per data bit, to a large extent, by the size of a single transistor, the number of transistors needed per memory cell, and the cell layout and architecture. The target market of the domain wall (DW)-motion Magnetic random access memory (MRAM) is high-speed memory macros embedded in a next generation System on a Chip. Compared with conventional MRAM, including spin transfer torque MRAM, the main advantage of DW-motion MRAM is the separation of the writing and read-out circuits and thus, the larger margin for the read-out levels. The racetrack memory is conceptually very different from MRAM.
Protecting private communications in cyber-physical systems through physical unclonable functions
Perez-Jimenez, Marina, Borja Bord Sanchez, Andrea Migliorini, Ramon Alcarria
abstractCyber-physical systems (CPS) are envisioned to change the whole of society. New engineered systems joining physical and digital solutions are being employed in industry, education, etc. These new systems are networked by default, and private information is shared among the different components related to users, critical infrastructures, or business operations. In this context, it is essential to encrypt those communication links to protect such information. However, even most complicated schemes based on hybrid (asymmetric and symmetric) solutions, finally require physical devices to store a secret key. This approach is cryptographically weak, as any person with physical access to the device could obtain that key. Therefore, in this paper we propose the use of physical unclonable functions (PUF) to generate secret keys for lightweight encryption schemes. Using PUFs, any attempt to capture the key is changing the original secret stream, and even manufacturers are not able to build two identical PUFs. The proposed key generator is based on magnetic materials and lightweight pseudorandom number generators to meet the low-cost and small size requirements of CPS. In particular, materials with an activated exchange-bias effect are employed, together with simple copper coils. The encryption process can be based on a simple XOR gate because of the robustness of the proposed key generator. In order to evaluate the performance of the proposed technology, an experimental validation based on simulation scenarios is also provided.
A bismuth triiodide monosheet on Bi2Se3(0001)
Polyakoy, Andrey, Katayoon Mohseni, German R. Castro, Juan Rubio-Zuazo, Alexander Zeugner, Anna Isaeva, Ying-Jiun Chen, Christian Tusche, Holger L. Meyerheim
abstractA stable Bil(3) monosheet has been grown for the first time on the (0001) surface of the topological insulator Bi2Se3 as confirmed by scanning tunnelling microscopy, surface X-ray diffraction, and X-ray photoemision spectroscopy. Bil(3) is deposited by molecular beam epitaxy from the crystalline BiTel precursor that undergoes decomposition sublimation. The key fragment of the bulk Bil3 structure, a∞2 [l-Bi-l] layer of edge-sharing Bil6 octahedra, is preserved in the ultra-thin film limit, but exhibits large atomic relaxations. The stacking sequence of the trilayers and alternations of the Bi-l distances in the monosheet are the same as in the bulk Bil3 structure. Momentum resolved photoemission spectroscopy indicates a direct band gap of 1.2 eV. The Dirac surface state is completely destroyed and a new flat band appears in the band gap of the Bil3 film that could be interpreted as an interface state.
Intrinsic stability of magnetic anti-skyrmions in the tetragonal inverse Heusler compound Mn1.4Pt0.9Pd0.1Sn
Saha, Rana, Abhay K. Srivastava, Tianping Ma, Jagannath Jena, Peter Werner, Vivek Kumar, Claudia Felser, S. S. P. Parkin
abstractMagnetic anti-skyrmions are one of several chiral spin textures that are of great current interest both for their topological characteristics and potential spintronic applications. Anti-skyrmions were recently observed in the inverse tetragonal Heusler material Mn1.4Pt0.9Pd0.1Sn. Here we show, using Lorentz transmission electron microscopy, that anti-skyrmions are found over a wide range of temperature and magnetic fields in wedged lamellae formed from single crystals of Mn1.4Pt0.9Pd0.1Sn for thicknesses ranging up to ∼ 250 nm. The temperature-field stability window of the anti-skyrmions varies little with thickness. Using micromagnetic simulations we show that this intrinsic stability of anti-skyrmions can be accounted for by the symmetry of the crystal lattice which is imposed on that of the Dzyaloshinskii-Moriya exchange interaction. These distinctive behaviors of anti-skyrmions makes them particularly attractive for spintronic applications.
Electric field control of phase transition and tunable resistive switching in SrFeO2.5
Saleem, Muhammad S, Bin Cui, Cheng Song, Yiming Sun, Youdi Gu, Ruiqi Zhang, Muhammad U Fayaz, Xiaofeng Zhou, Peter Werner, S. S. P. Parkin, Feng Pan
abstractSrFeOx (SFOx) compounds exhibit ionic conduction and oxygen related phase transformation, having potential applications in solid oxide fuel cells, smart windows, and memristive devices. The phase transformation in SFOx typically requires a thermal annealing process under various pressure conditions, hindering their practical applications. Here, we have achieved a reversible phase transition from brownmillerite (BM) to perovskite (PV) in SrFeO2.5 (SFO2.5) films through ionic liquid (IL) gating. The real-time phase transformation is imaged using in situ high resolution transmission electron microscopy. The magnetic transition in SFO2.5 is identified by fabricating an assisted La0.7Sr0.3MnO3 (LSMO) bottom layer. The IL-gating-converted PV phase of a SrFeO3−δ (SFO3−δ) layer shows a ferromagnetic-like behavior but applies a huge pinning effect on LSMO magnetic moments, which consequently leads to a prominent exchange bias phenomenon, suggesting an uncompensated helical magnetic structure of SFO3−δ. On the other hand, the suppression of both magnetic and exchange coupling signals for a BM-phased SFO2.5 layer elucidates its fully compensated G-type antiferromagnetic nature. We also demonstrated that the phase transition by IL gating is an effective pathway to tune the resistive switching parameters, such as set, reset, and high/low-resistance ratio in SFO2.5-based resistive random-access memory devices.
In-plane ferroelectric tunnel junction
Shen, Huitao, Junwei Liu, Kai Chang, Liang Fu
abstractFerroelectric materals are an important platform for the realization of nonvolatile memories. So far, existing ferroelectric memory devices have utilized out-of-plane polarization in ferroelectric thin films. In this paper, we propose a type of random-access memory (RAM) based on ferroelectric thin films with in-plane polarization, called an "in-plane ferroelectric tunnel junction."" Apart from nonvolatility, lower power usage, and a faster writing operation compared with traditional dynamic RAMs, our proposal has the advantage of a faster reading operation and a nondestructive reading process, thus overcoming the write-after-read problem that exists widely in current ferroelectric RAMs. The recent discovered room-temperature ferroelectric IV-VI semiconductor thin films are a promising material platform for the realization of our proposal.
Observation of robust Néel skyrmions in metallic PtMnGa
Srivastava, Abhay K., Parul Devi, Ankit K. Sharma, Tianping Ma, Hakan Deniz, Holger L. Meyerheim, Claudia Felser, S. S. P. Parkin
abstractOver the past decade the family of chiral noncollinear spin textures has continued to expand with the observation in metallic compounds of Bloch-like skyrmions in several B20 compounds, and antiskyrmions in a tetragonal inverse Heusler. Néel like skyrmions in bulk crystals with broken inversion symmetry have recently been seen in two distinct nonmetallic compounds, GaV4S8 and VOSe2O5 at low temperatures (below ≈ 13 K) only. Here, the first observation of bulk Néel skyrmions in a metallic compound PtMnGa and, moreover, at high temperatures up to ≈ 220 K is reported. Lorentz transmission electron microscopy reveals the chiral Néel character of the skyrmions. A strong variation is reported of the size of the skyrmions on the thickness of the lamella in which they are confined, varying by a factor of 7 as the thickness is varied from ≈ 90 nm to ≈ 4 μm. Moreover, the skyrmions are highly robust to in-plane magnetic fields and can be stabilized in a zero magnetic field using suitable field-cooling protocols over a very broad temperature range to as low as 5 K. These properties, together with the possibility of manipulating skyrmions in metallic PtMnGa via current induced spin-orbit torques, make them extremely exciting for future spintronic applications.
Epitaxial growth, structural characterization, and exchange bias of noncollinear antiferromagnetic Mn3Ir thin films
Taylor, James M., Edouard Lesne, Anastasios Markou, Fasil Kida Dejene, Benedikt Ernst, Adel Kalache, Kumari Gau Rana, Neeraj Kumar, Peter Werner, Claudia Felser, S. S. P. Parkin
abstractAntiferromagnetic materials are of great interest for spintronics. Here we present a comprehensive study of the growth, structural characterization, and resulting magnetic properties of thin films of the noncollinear antiferromagnet Mn3Ir. Using epitaxial engineering on MgO (001) and Al2O3 (0001) single-crystal substrates, we control the growth of cubic gamma-Mn3Ir in both (001) and (111) crystal orientations, and discuss the optimization of growth conditions to achieve high-quality crystal structures with low surface roughness. Exchange bias is studied in bilayers, with exchange bias fields as large as -29 mT (equivalent to a unidirectional anisotropy constant of 0.115 erg cm−2 or 11.5 nJ cm−2) measured in Mn3Ir (111)/Permalloy heterostructures at room temperature. In addition, a distinct dependence of blocking temperature on in-plane crystallographic direction in Mn3Ir (001)/Permalloy bilayers is observed. These findings are discussed in the context of antiferromagnetic domain structures, and will inform progress towards chiral antiferromagnetic spintronic devices.
Magnetic and electrical transport signatures of uncompensated moments in epitaxial thin films of the noncollinear antiferromagnet Mn3Ir
Taylor, James M., Edouard Lesne, Anastasios Markou, Fasil Kida Dejene, Pranava Ke Sivakumar, Simon Poellath, Kumari Gau Rana, Neeraj Kumar, Chen Luo, Hanjo Ryll, Florin Radu, Florian Kronast, Peter Werner, Christian Back, Claudia Felser, S. S. P. Parkin
abstractNoncollinear antiferromagnets, with either an L12 cubic crystal lattice (e.g., Mn3Ir and Mn3Pt) or a D019 hexagonal structure (e.g., Mn3Sn and Mn3Ge), exhibit a number of phenomena of interest to topological spintronics. Among the cubic systems, for example, tetragonally distorted Mn3Pt exhibits an intrinsic anomalous Hall effect (AHE). However, Mn3Pt only enters a noncollinear magnetic phase close to the stoichiometric composition and at suitably large thicknesses. Therefore, we turn our attention to Mn3Ir, the material of choice for use in exchange bias heterostructures. In this letter, we investigate the magnetic and electrical transport properties of epitaxially grown, face-centered-cubic γ-Mn3Ir thin films with (111) crystal orientation. Relaxed films of 10 nm thickness exhibit an ordinary Hall effect, with a hole-type carrier concentration of (1.500 ± 0.002) x 1023cm−3. On the other hand, TEM characterization demonstrates that ultrathin 3 nm films grow with significant in-plane tensile strain. This may explain a small net magnetic moment, observed at low temperatures, shown by X-ray magnetic circular dichroism spectroscopy to arise from uncompensated Mn spins. Being of the order of 0.02 μB/atom, this dominates electrical transport behavior, leading to a small AHE and negative magnetoresistance. These results are discussed in terms of crystal microstructure and chiral domain behavior, with spatially resolved XML(C)D-PEEM supporting the conclusion that small antiferromagnetic domains, < 20nm in size, with differing chirality account for the absence of observed Berry curvature driven magnetotransport effects.
Anomalous and topological Hall effects in epitaxial thin films of the noncollinear antiferromagnet Mn3Sn
Taylor, James M., Anastasios Markou, Edouard Lesne, Pranava Ke Sivakumar, Chen Luo, Florin Radu, Peter Werner, Claudia Felser, S. S. P. Parkin
abstractNoncollinear antiferromagnets with a D019 (spacegroup = 194, P63/mmc) hexagonal structure have garnered much attention for their potential applications in topological spintronics. Here, we report the deposition of continuous epitaxial thin films of such a material, Mn3Sn, and characterize their crystal structure using a combination of x-ray diffraction and transmission electron microscopy. Growth of Mn3Sn films with both (0001) c-axis orientation and (4043) texture is achieved. In the latter case, the thin films exhibit a small uncompensated Mn moment in the basal plane, quantified via magnetometry and x-ray magnetic circular dichroism experiments. This cannot account for the large anomalous Hall effect simultaneously observed in these films, even at room temperature, with magnitude σxy(μ0H = 0 T) = 21 Ω−1 cm−1 and coercive field μ0Hc = 1.3 T. We attribute the origin of this anomalous Hall effect to momentum-space Berry curvature arising from the symmetry-breaking inverse triangular spin structure of Mn3Sn. Upon cooling through the transition to a glassy ferromagnetic state at around 50 K, a peak in the Hall resistivity close to the coercive field emerges. This indicates the onset of a topological Hall effect contribution, arising from a nonzero scalar spin chirality that generates a real-space Berry phase. We demonstrate that the polarity of this topological Hall effect, and hence the chiral nature of the noncoplanar magnetic structure driving it, can be controlled using different field-cooling conditions.
Band structure engineering of chemically tunable LnSbTe (Ln = La, Ce, Pr)
Weiland, Ashley, David G. Chaparro, Maia G. Vergniory, Elena Derunova, Jiho Yoon, Iain W. H. Oswald, Gregory T. McCandless, Mazhar Ali, Julia Y. Chan
abstractThe ZrSiS family of compounds has garnered interest as Dirac nodal-line semimetals and offers an approach to study structural motifs coupled with electronic features, such as Dirac crossings. CeSbTe, of the ZrSiS/PbFCl structure type, is of interest due to its magnetically tunable topological states. The crystal structure consists of rare earth capped square nets separating the magnetic Ce-Te layers. In this work, we report the single crystal growth, magnetic properties, and electronic structures of LnSb1−xBixTe (Ln = La, Ce, Pr; x ∼ 0.2) and CeBiTe, adopting the CeSbTe crystal structure, and the implication of tuning the electronic properties by chemical substitution.
Chiral exchange drag and chirality oscillations in synthetic antiferromagnets
Yang, See-Hun, Chirag Garg, S. S. P. Parkin
abstractLong-range interactions between quasiparticles give rise to a "drag" that affects the fundamental properties of many systems in condensed matter physics. Drag typically involves the exchange of linear momentum between quasiparticles and strongly influences their transport properties. Here, we describe a kind of drag that involves the exchange of angular momentum between two current-driven magnetic domain walls. The motions of the domain walls are correlated and determined by the strength of the drag. When the drag is below a threshold value, the domain walls move together at a constant intermediate velocity with a steady leakage of angular momentum from the faster to the slower wall. However, we find that when the drag exceeds a threshold value, a different dynamic can take place in which the faster domain wall"s magnetization oscillates synchronously with a precessional motion of the slower domain wall"s magnetization, and angular momentum is continuously transferred between them. Our findings demonstrate a method for delivering spin angular momentum remotely to magnetic entities that otherwise could not be manipulated directly by current, for example, by coupling domain walls or other non-collinear spin textures in metallic and insulating media.
Novel stable 3D stainless steel-based electrodes for efficient water splitting
Zhang, Haojie, Juliana Ma de Souza e Silva, Xubin Lu, Cristine S de Oliveira, Bin Cui, Xiaopeng Li, Chao Lin, Stefan L. Schweizer, A. Wouter Maijenburg, Michael Bron, Ralf B. Wehrspohn
abstractThe stability of electrocatalysts grown on substrates is a significant challenge for the construction of 3-dimensional (3D) stainless-steel (SS)-based electrodes for highly efficient water splitting. This paper presents an efficient and universal process to enhance the interfacial interaction between SS and highly active electrocatalysts for the preparation of 3D electrodes through the formation of an interfacial network of carbon nanotubes (CNTs) on the SS. Nanoscale X-ray computed tomography and focused ion beam are used to visualize the interface between CNTs and SS, and 3D structure of CNT/SS electrodes. The strongly interconnected CNTs network increases the surface area of the SS support that benefits the modification of highly active electrocatalysts and also serves as an electron/charge-conductive highway between electrocatalysts and support. The electrocatalysts on CNT/SS further improve hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performances, respectively, of the 3D electrodes. While compared to the SS-based electrodes reported recently, Pt/OxCNT/SS shows the best HER activity over wide pH range and RuO2/OxCNT/SS exhibits a comparable OER performance in neutral and alkaline electrolyte. An efficient approach is reported to combine highly active electrocatalysts with SS for the preparation of active and stable 3D electrodes that can be further explored in various areas.
Effect of interfacial insertion layers on the spin-orbit torque in W(O)|CoFeB heterostructures
Zhang, Jie, Timothy Phung, Brian P. Hughes, See-Hun Yang, Chirag Garg, Yong Jiang, S. S. P. Parkin
abstractWe report on an experimental investigation of spin-orbit torque (SOT) in W(O)|CoFeB heterostructures where a thin insertion layer with negligible spin-orbit coupling is inserted at the W(O)|CoFeB interface. The SOT is found to be suppressed with the addition of the insertion layer, contrary to estimates using the transparency formalism. In addition, the SOT, as quantified by the spin Hall angle remains constant at -50% for W(O) thicknesses down to 2 nm. Our data is thus consistent with an interfacial SOT mechanism in the W(O)|CoFeB system.
A hydrated crystalline calcium carbonate phase: Calcium carbonate hemihydrate
Zou, Zhaoyong, Wouter J. Habraken, Galina Matveeva, Anders C. Jensen, Luca Bertinetti, Matthew A. Hood, Chang-yu Sun, Pupa U. P. Gilbert, Iryna Polishchuk, Boaz Pokroy, Julia Mahamid, Yael Politi, Steve Weiner, Peter Werner, Sebastian Bette, Robert Dinnebier, Ute Kolb, Emil Zolotoyabko, Peter Fratzl
abstractAs one of the most abundant materials in the world, calcium carbonate, CaCO3, is the main constituent of the skeletons and shells of various marine organisms. It is used in the cement industry and plays a crucial role in the global carbon cycle and formation of sedimentary rocks. For more than a century, only three polymorphs of pure CaCO3-calcite, aragonite, and vaterite-were known to exist at ambient conditions, as well as two hydrated crystal phases, monohydrocalcite (CaCO3·1H2O) and ikaite (CaCO3·6H2O). While investigating the role of magnesium ions in crystallization pathways of amorphous calcium carbonate, we unexpectedly discovered an unknown crystalline phase, hemihydrate CaCO3·1/2H2O, with monoclinic structure. This discovery may have important implications in biomineralization, geology, and industrial processes based on hydration of CaCO3.