Chiral magnets in the B20 crystal structure host a peculiar spin texture in the form of a topologically stable skyrmion lattice. However, the helical transition temperature (TC) of these compounds is below room temperature, which limits their potential in spintronics applications. Here, a data-driven approach is demonstrated, which integrates density functional theory (DFT) calculations with machine learning (ML) in search of alloying elements that will enhance the TC of known B20 compounds. Initial DFT screening led to the identification of chromium (Cr) and tin (Sn) as potential substituents for alloy design. Then, trained ML models predict Sn substitution to be more promising than Cr-substitution for tuning the TC of FeGe. The magnetic exchange energy calculated from DFT validates the promise of Sn as an effective alloying element for enhancing the TC in Fe(Ge,Sn) compounds. New B20 chiral magnets are recommended for experimental investigation.

Spin-transfer-torque magnetoresistive random-access memory (STT-MRAM) is an emerging nonvolatile memory that uses magnetic tunnel junctions (MTJs) to store information. MTJs with a crystalline MgO(001) tunnel barrier sandwiched between ferromagnetic layers, such as CoFeB, exhibit giant tunnel magnetoresistance, which is used to readout the STT-MRAM. Writing of STT-MRAM is based on current-induced magnetization reversal, called STT switching. STT-MRAM with perpendicular magnetization is especially important for high-density and low-power-consuming memory applications such as embedded memory for large-scale integrated circuit. For STT-MRAM to replace ultrahigh-density dynamic random-access memory, however, there are still technological challenges concerning the materials and fabrication processes of MTJs. This article reviews the physics and materials science of MTJs for STT-MRAM. We also discuss the importance of new MTJ materials and processes for next-generation ultrahigh-density MRAM.

Increasing the density of data storage is crucial to the future of inexpensive digital technology. The large majority of storage in the “Cloud” consists of magnetic hard-disk drives. The continued evolution of this USD$30 billion industry depends on the commercial introduction of heat-assisted magnetic recording (HAMR). This technology uses heat from a laser beam confined well below the diffraction limit, <50-nm wide, to write to media near 450°C with high magnetic anisotropy that would normally be unwriteable under available magnetic fields. This high anisotropy guarantees thermal stability even for grain sizes around 5-nm diameter, which are necessary for major increases in storage density. In this article and in the articles in this issue, we introduce HAMR requirements and discuss its numerous interdisciplinary materials challenges, including high-temperature/efficient plasmonic materials, low-loss optical materials, highly ordered/thermally anisotropic nanoscale magnetic grains, block copolymers for directed assembly below 10 nm, high-temperature nanometer-thick coatings/lubricants, materials/interfaces to control heat flow at nanometer length scales, and advanced spintronic materials.

We report on the exploration of perpendicular exchange bias in iron platinum/nickel oxide (FePt/NiO) bilayer thin films grown using pulsed laser deposition (PLD) on MgO (100) substrates. Exchange bias is an important property for giant magnetoresistance, and, as such has promise for applications in spin valves, magnetic sensors and magnetic random access memory. The magnetic L10 phase of FePt is known for having high perpendicular magnetic anisotropy, tunable coercivity/grain size and large magnetic storage density. The FePt layer was first deposited directly on MgO, followed by the deposition of the NiO layer on top of the FePt layer. The coercivity of the L10 FePt layer was tuned during growth to form a hard or soft magnetic layer. The FePt/NiO thin films grown for this study exhibit perpendicular exchange bias at 5K, as quantified using our SQUID measurements. XRD confirms parallel plane ordering between the MgO (200), FePt (002) and NiO (111) atomic planes while cross sectional TEM confirms the epitaxial growth of L10-FePt(001)<100>//MgO(100)<001> and the preferential growth of NiO on top of the FePt. Films of only FePt were grown to examine the surface architecture of the ferromagnetic layer and thus the interface of the FePt/NiO bilayer. The results from our XRD, TEM and magnetometry characterization of the FePt films and FePt/NiO bilayer thin films will be discussed.

Anomalous Hall effect was observed at room temperature in MOCVD-grown GaGdN from a (TMHD)3Gd source, which can contain oxygen in its organic ligand. GaN, and GaGdN grown using a Cp3Gd precursor which does not contain oxygen only showed the ordinary Hall effect. This indicates that oxygen could have a role in magnetic properties of GaGdN. The relationship between the anomalous Hall conductivity and longitudinal conductivity indicated that metallic conduction, hopping of carriers, and scattering-independent mechanisms are likely responsible for the ferromagnetism. However, this still requires further clarification.

The electronic and transport properties of graphene nanoribbons strongly depends on different types of adatoms. Oxygen as adatom on graphene is expected to resemble oxidized graphene sheets and enable in understanding their transport properties. Here, we report the transport properties of oxygen adsorbed zigzag edge saturated graphene nanoribbon. It is interesting to note that increasing the number of oxygen adatoms on graphene sheets lift the spin degeneracy as observed in the transmission profile of graphene nanoribbons. The relative orientation of the oxygen atom on the graphene basal plane is detrimental to flow of spin current in the nanoribbon.

Optical transmission spectra are collected in the ferromagnetic state of GdN at various temperatures. The temperature dependent extinction coefficient extracted from the transmission measurements show that the conduction and valence band states are spin polarized. The results confirm the LSDA+U estimates of the energy gap associated with the majority/minority-spins and also the magnitude of the spin splitting.

We report on the establishment of a new lab-scale experimental capability for Spin and Angular Resolved Photoemission Spectroscopy (SARPES) for the study of valleytronics related materials. The ARPES capabilities of the system were demonstrated by measurement on gold [Au(111)] and molybdenum disulphide (MoS2) single crystals and the full functionality of the spin detector was also verified. Experimental results are compared with theoretical modeling by ab-initio band structure calculations. We discuss the potential scope of measurement that this experimental setup affords for investigating spin-related properties (e.g. spin-orbit coupling, valley transport, etc.) in layered materials.

Quantum information and computing are at the forefront of computer science, but their implementation relies on significant developments in materials science. In particular, suitable, lattice-matched substrates for two promising approaches—electrostatically defined quantum dots in Si/SiGe heterostructures, and superconducting circuits containing Josephson junctions—do not exist. Instead, these approaches rely on metamorphic substrates. In this article, we focus on the general structure and requirements of SiGe quantum dot heterostructures, the demands they impose on the underlying substrate, and the impact that properties of the metamorphic substrate have on device performance. Superconductor Josephson junction materials are briefly discussed in a similar fashion, and opportunities for future developments in both systems are described.

In the previous work, it is reported that the Spin-Seebeck effect (SSE), which refer to the generation of a spin current from a temperature gradient, can be enhanced by Fe interface treatment. Here, we investigated the Fe thickness (dFe) dependency of spin-Seebeck voltage (VSSE) and mixing conductance (gr) in Pt/Fe/Bi:YIG/SGGG system. As a result, magnitude of VSSE had a peak at dFe ≓ 1 ML (monolayer , ≓ 0.3 mm), and also increase of gr was saturated at this point. It suggests that VSSE increase with increasing gr when dFe is smaller than 1.0 ML. For the case in which dFe is larger than 1.0ML, however, VSSE decreases due to a spin current decay in Fe layer with a constant gr. These experimental results are consistent with previous theoretical works.

The past decade has seen remarkable progress in the development of the nitrogen-vacancy (NV) defect center in diamond, which is one of the leading candidates for quantum information technologies. The success of the NV center as a solid-state qubit has stimulated an active search for similar defect spins in other technologically important and mature semiconductors, such as silicon carbide. If successfully combined with the advanced microfabrication techniques available to such materials, coherent quantum control of defect spins could potentially lead to semiconductor-based, wafer-scale quantum technologies that make use of exotic quantum mechanical phenomena like entanglement. In this article, we describe the robust spin property of the NV center and the current status of NV center research for quantum information technologies. We then outline first-principles computational modeling techniques based on density functional theory to efficiently search for potential spin defects in nondiamond hosts suitable for quantum information applications. The combination of computational modeling and experimentation has proven invaluable in this area, and we describe the successful interplay between theory and experiment achieved with the divacancy spin qubit in silicon carbide.

Thin film Ti doped ZnO (Ti-ZnO) film were grown on sapphire (0001) substrate by RF and DC magnetron sputtering. Films were grown at a substrate temperature of 250 °C with different Ti/Zn concentration. Surface chemical study of the samples was performed by X-ray photoelectron spectroscopy to determine the stoichiometry and Ti/Zn ratio for all samples. Surface morphology of the samples were studied by atomic force microscopy. X-ray diffraction was carried out to determine the crystallinity of the film. No secondary phases of TixOy was observed. We observed a slight increase in the lattice constant with the increase in Ti concentration in ZnO. No ferromagnetic signal was observed for any of the samples. However, some samples showed super-paramagnetic phase.

The class of topological insulator materials is one of the frontier topics of condensed matter physics. The great success of this field is due to the conceptual breakthroughs in theories for topological electronic states and is strongly motivated by the rich variety of material realizations, thus making the theories testable, the experiments operable, and the applications possible. First-principles calculations have demonstrated unprecedented predictive power for material selection and design. In this article, we review recent progress in this field with a focus on the role of first-principles calculations. In particular, we introduce the Wilson loop method for the determination of topological invariants and discuss the band inversion mechanism for the selection of topological materials. Recent progress in quantum anomalous Hall insulators, large-gap quantum spin Hall insulators, and correlated topological insulators is also covered.

Active research is ongoing in logic devices beyond complementary metal–oxide–semiconductor electronics. One of the most promising classes of such devices is spintronic/nanomagnetic devices. Switching of magnetization by spin torque (ST) demonstrated in spintronic devices results in relatively high switching energy. An attractive option for lowering switching energy is magnetoelectric (ME) switching achieved by placing other materials (mostly oxides) adjacent to ferromagnets. We review recent experiments on ME switching, classify them according to the ME phenomena into surface anisotropy, exchange bias, and magnetostrictive, and compare switching parameters for these classes. Then, we perform micromagnetic simulations of switching by the effective ME field of both stand-alone nanomagnets and spintronic interconnects. We determine the threshold values of ME field for switching and the resulting switching time. These switching requirements are incorporated into the previously developed benchmarking framework for spintronic logic devices and circuits. We conclude that ME switching results in 1 to 2 orders of magnitude improvement of switching energy and several time improvement of switching delay compared with ST switching across various schemes of spin logic devices.

A number of studies have suggested that molecular materials could offer similar performance as, or even potentially supersede, those of inorganic materials in spintronics devices. Radically new spintronics functionalities, unavailable with conventional inorganic materials, could stem from the interface between ferromagnetic (FM) and molecular materials, giving rise to the so-called “spinterface” field. In this article, we review the fundamental concepts, recent experiments, and perspectives in this fast rising field, where the functionality is brought from the bulk to the ultimate downscaled device: the interface. The article shows how spin-dependent hybridization at the FM metal/molecule interface can lead to induced spin polarization in the molecular orbitals thanks to spin-dependent broadening and energy shifting of the molecular levels. Interfacial spin polarization can then be tailored thanks to chemical interactions. Examples of enhancement and reversal are given, and we highlight how this spin-dependent hybridization opens a new door for the spintronics crafting of multifunctionality through chemical designing and tuning on the molecular scale.

Organic materials provide a unique platform for exploiting the spin of the electron—a field dubbed organic spintronics. Originally, this was mostly motivated by the notion that because of weak spin-orbit coupling, due to the small mass elements in organics and small hyperfine field coupling, organic matter typically displays a very long electron spin coherence time. More recently, however, it was found that organics provide a special class of spintronic materials for many other reasons—several of which are discussed throughout this issue. Over the past decade, there has been a growing interest in utilizing the molecular spin state as a quantum of information, aiming to develop multifunctional molecular spintronics for memory, sensing, and logic applications. The aim of this issue is to stimulate the interest of researchers by bringing to their attention the vast possibilities not only for unexpected science but also for the enormous potential for developing new functionalities and applications. The six articles in this issue deal with some of the breakthrough work that has been ongoing in this field in recent years.

Magnetic metal-organic complexes and coordination polymer frameworks can exhibit a transition between two different spin states of the integrated transition-metal ion, an attribute known as a spin-crossover (SCO) transition. This is a spectacular phenomenon that provides magnetic bi-stability and reversible spin-switchability to the material. Consequently, the magnetic state of the metal-organic center can be externally steered by temperature, pressure, or light irradiation. SCO molecules therefore are promising materials for various technological applications, such as spintronics devices, photo-switches, color displays, and information storage units. In spite of the importance of SCO materials in spintronics and other applications, the materials-specific understanding of the SCO phenomenon has remained a challenge. Here we survey recent developments in first-principles computational design of SCO metal-organic materials. A major outcome of recent state-of-the-art investigations is that an accurate quantitative description and even computational design of SCO materials can be provided by density functional theory-based electronic structure calculations combined with ab initio molecular dynamics simulations.

The effects of a magnetic field on the current in sandwich devices of a nonmagnetic material in-between two ferromagnetic electrodes are well known. However, magnetic-field effects also occur in the responses of devices of organic semiconductors sandwiched in-between non-ferromagnetic electrodes, providing an entirely new route toward organic spintronics. The precise origins of these “intrinsic” magnetic field effects are still unclear. They appear to be related to spin-selective reactions between paramagnetic entities such as electrons, holes, and triplet excitons. We present an overview of these effects and discuss three recent developments that shed new light on them: (1) tuning of the effects in molecularly engineered systems, (2) the discovery of ultrahigh magnetoresistance in molecular wires, and (3) the discovery of “fringe-field” magnetoresistance.

Organic materials are fascinating and promising candidates for nanoscale spintronic devices and may open viable routes toward quantum computing. Previous experiments on spin transport in organic devices, through break junctions or spin valves, unveiled exciting new frontiers of molecular magnetism. However, much more effort is needed to understand the properties of organic/magnetic interfaces at a microscopic level. In this article, we show how spin-polarized scanning tunneling microscopy and spectroscopy (SP-STM/STS) can provide unprecedented insights into organic/magnetic interfaces as an initial step toward favorably tailoring such interfaces in order to increase device efficiency. Based on the unique combination of spin-sensitivity, atomic-scale spatial resolution, and high-energy resolution, SP-STM/STS has proven to be an invaluable method for exploring spatial and bias dependences of spin-polarized currents through individual molecules as well as for revealing individual spin-split molecular orbitals interacting with ferromagnetic substrates.

We review the first 10 years of research on organic spin-valve devices in the field of organic spintronics. The device figure of merit, magnetoresistance, is governed by the hyperfine interaction of the organic interlayer and the ability of the ferromagnetic electrodes to inject spin-polarized carriers. By choosing a deuterated π-conjugated polymer with a relatively long spin diffusion length as the organic interlayer and using a thin LiF buffer layer to raise the Fermi level of the cathode, a bipolar spin-valve device could be obtained in which the electroluminescence emission intensity is controlled by an external magnetic field. We show that the underlying physics of this spin-organic light-emitting diode is very different from that of a unipolar organic spin valve because of the magnetic properties of the spin-polarized bipolar space charge limited current in the device.