Recent Spintronic News - Page 2

Researchers at Harvard University, the University of Chicago, the Bavarian Academy of Sciences, the Technical University of Munich, and Argonne National Laboratory have demonstrated a new way to protect fragile quantum information using nothing but mechanical vibrations - phonons, the quantum particles of sound.

The work builds on an approach to quantum networking in which the spin of an electron tied to a defect in diamond, known as a silicon-vacancy center, serves as a stationary quantum memory, while phonons carry information between memory nodes. Phonons have real advantages over photons at chip scale: at a given frequency their wavelengths are far shorter, allowing smaller and more tightly integrated devices, and they couple readily to both solid-state spins and electromagnetic fields, making them useful building blocks for hybrid systems that mix different qubit types. The team, based in the lab of Harvard's Marko Lončar, has previously built "phononic cavities" that house a silicon-vacancy qubit and trap vibrations so they interact strongly with its spin.

Giacomo Sala, an experimental physicist at the Paul Scherrer Institute's (PSI) Center for Neutron and Muon Science, has been awarded a European Research Council (ERC) Starting Grant worth €2.3 million (about US$2.7 million) over five years for Q-GEOMSPIN, a project aiming to experimentally connect spintronics with the emerging field of quantum geometry for the first time.

Spintronics, which exploits the intrinsic spin of electrons alongside their charge to store and process information, has existed as a field for three decades and underpinned the giant magnetoresistance effect that multiplied hard drive storage density in the 1980s. Quantum geometry, by contrast, describes the geometric structure of electron wave functions inside a solid. Sala's project focuses specifically on a subfield called the quantum metric, which he compares to how mass curves space in general relativity: just as that curvature explains the Earth's orbit around the sun, quantum metric describes a curvature of momentum space that deflects electrons as they move through a material. Theoretical work has suggested this curvature could give rise to spintronic effects that have so far gone unrecognized, a connection Sala says has not yet been tested experimentally.

Researchers at Helmholtz-Zentrum Berlin (HZB), KAIST, the Technical University of Munich, the Max Planck Institute for Chemical Physics of Solids, the Technical University of Dresden, the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, the Paul Scherrer Institut's Swiss Light Source, and RIKEN's Center for Emergent Matter Science have shown that magnetic fields of just a few millitesla, applied in-plane rather than perpendicular to a sample, can continuously rotate and reshape the chiral magnetic stripe domains of a room-temperature noncentrosymmetric magnet, offering a new vector-field-based way to control magnetic domain orientation.

Micromagnetic simulations show how a small magnetic field in plane with the magnetic stripes can change the magnetic texture from a stripe pattern to a fan pattern. Image credit: HZB

Noncentrosymmetric magnets, which lack inversion symmetry, host a competition between conventional exchange interaction and the antisymmetric Dzyaloshinskii-Moriya interaction (DMI), the effect responsible for the chirality of textures such as helices, cycloids, and skyrmions. How that competition plays out depends heavily on a material's crystal symmetry, and most experimental work on it has relied on Lorentz transmission electron microscopy (LTEM), a technique generally limited to magnetic field tilt angles of 45 degrees or less. That has left the response of these materials to genuinely in-plane fields, and the role of a material's full three-dimensional field environment, largely unexplored.

Researchers at Wenzhou University, MIT, the Shanghai Institute of Technical Physics (Chinese Academy of Sciences), the University of Chinese Academy of Sciences, Caltech, the Hong Kong University of Science and Technology, and Fuzhou University have developed a general method for growing large-scale, single-crystalline films of two-dimensional metal oxides that are directly compatible with silicon technology - a longstanding barrier to building spintronic, ferroelectric, and neuromorphic components directly onto conventional chips.

Hybrid integration of 2D single-crystal metal oxides with silicon circuits is central to the "More-than-Moore" roadmap for extending chip functionality beyond simple transistor scaling, but growing such oxides as true single crystals has proven difficult. Conventional epitaxy relies on strong chemical bonding to lock a growing film into registry with its substrate, which causes defects when integrating chemically dissimilar materials like oxides and silicon. Van der Waals epitaxy on layered substrates such as mica avoids that problem by using weak, non-directional interactions instead, but the resulting surfaces are typically too chemically inert to guide film growth in a single orientation, so films tend to form as a mosaic of randomly oriented crystallites rather than a true single crystal. The team's solution was to reconstruct the oxygen atomic plane exposed at the surface of cleaved mica. Quantum mechanics calculations showed that this reconstruction creates a periodic potential landscape that energetically favors one crystallographic orientation for incoming oxide atoms, without requiring strong chemical bonds - effectively letting correctly oriented crystal nuclei grow faster and dominate while misoriented ones are starved of material.

Researchers at Carnegie Mellon University, Boston College, the University of California, Los Angeles, the Air Force Research Laboratory, Kansas State University, Japan's National Institute for Materials Science, and Harvard University have experimentally demonstrated an in-plane anomalous Hall effect (AHE) in a low-dimensional heterostructure, overturning the long-held assumption that the anomalous Hall response can only be driven by a material's out-of-plane magnetization.

The Hall effect, first observed in 1879, has served for well over a century as a core tool for probing a material's electronic properties: applying a magnetic field perpendicular to a conducting material deflects moving charges and produces a measurable voltage, revealing whether current is carried by positive or negative charge carriers and how many are flowing. In magnetic materials, the anomalous Hall effect adds a magnetization-dependent contribution to that signal, but symmetry constraints have generally required that response to scale with the out-of-plane component of magnetization alone. An in-plane version of the effect had been theoretically proposed but never demonstrated, largely because it requires a magnetic material with a very specific, reduced crystalline symmetry that is difficult to realize.

Researchers at Shenzhen University, the Japan Atomic Energy Agency, the National Institutes for Quantum Science and Technology (QST), the University of Tokyo, the University of Science and Technology of China, Xi'an Jiaotong University, Shenzhen Technology University (SZTU), and The Hong Kong Polytechnic University, have provided the first element-resolved confirmation of intrinsic carbon ferromagnetism at room temperature in a bulk, wafer-scale material. The result, obtained in a hyper-porous graphene network (HGN) grown across a 2-inch silicon wafer, adds carbon to the small list of room-temperature magnetic materials and offers a new, structurally tunable platform for exploring spintronic and magnetic applications of carbon allotropes.

Structural features of the hyper-porous graphene network (HGN). Structural characterization of the (HGN). (a) Optical image of HGN on a 2-inch Si wafer. (b) TEM image showing nanoscale pores. (c) Converted TEM sketch with pores (<2 nm) as hollow islands. (d-f), Plan-view HAADF TEM images: overview with pores (d), zoomed-in cross-linked edges (e), and atomic detail with 0.35 nm interlayer and 0.21 nm zigzag edge spacing (f). (g-i) Side-view TEM images: vertical layers (g), crosslinking features (h), and 0.12 nm armchair spacing (i). Image from: Advanced Materials
 

Claims of intrinsic magnetism in carbon have long been difficult to establish, since even a trace of ordinary magnetic contamination, iron, cobalt, or nickel, can produce a magnetic signal comparable to the faint ferromagnetism reported in some carbon systems, which typically sits near 10⁻³ emu/g or below in bulk graphite. Prior demonstrations of edge-localized magnetism in graphene nanoribbons and multi-spin nanographene molecules showed the underlying physics could work at the nanoscale, but establishing the same effect reliably in bulk carbon had remained an open problem, requiring evidence that carbon itself, not a contaminant, carries the magnetism, and a structural handle whose removal reversibly weakens the effect.

Researchers at Rice University, together with the University of Minnesota and Switzerland's Paul Scherrer Institute, working with contributing researchers from the Gwangju Institute of Science and Technology, Kyung Hee University, and Myongji University in South Korea, the University of Illinois Urbana-Champaign, the University of West Bohemia in the Czech Republic, and beamline scientists at Lawrence Berkeley National Laboratory's Advanced Light Source and Brookhaven National Laboratory's National Synchrotron Light Source II, have found that ultrathin, epitaxially strained films of ruthenium dioxide (RuO₂) display a spin texture consistent with altermagnetism, a form of magnetic order the material's bulk and thick-film forms have consistently failed to show despite RuO₂ standing for years as one of altermagnetism's leading candidate materials. 

 Illustration of strain-induced emergent magnetism in ultrathin RuO₂/TiO₂. Possible theoretic altermagnetic spin density is rendered with orange and blue visual effects in the top RuO₂ layers using AI. Credit: Rice University/Yichen Zhang.

Using spin-resolved angle-resolved photoemission spectroscopy (ARPES) on a 2.7-nanometer-thick, substrate-strained RuO₂ film, the team observed a spin texture combining mirror-odd and mirror-even components that a comprehensive symmetry analysis rules out explaining through nonmagnetic effects, pointing instead to intrinsically broken time-reversal symmetry.

Researchers at the National University of Singapore (NUS), led by Assistant Professor Ahmet Avsar of the university's Centre for Advanced 2D Materials, have combined a record-fidelity graphene spin-transport platform with magnetic-proximity band engineering to move graphene closer to practical spin-logic and spin-memory devices, across two complementary studies. The work targets one of graphene spintronics' core limitations: interfacial disorder at the electrical contacts that inject and detect spin, which has historically scrambled spin information before it can be read out electrically.

The first study rebuilt the graphene spin-device fabrication process around an inert-glovebox van der Waals assembly, laminating and cleaning the stack to produce atomically flat hexagonal boron nitride (h-BN) tunnel barriers rather than the oxide barriers more commonly used in graphene spin valves. That interface quality translated directly into device performance: nonlocal spin signals reached up to 1.6 kΩ at 2.5 K, spin polarization approached 90% (89% in the lead device), spin lifetime measured about 2.04 nanoseconds with a spin diffusion length of about 4.74 μm, and gate-tunable magnetoresistance exceeded 80%. Critically for eventual device use, the effect persisted at room temperature, where the same device retained a nonlocal spin resistance of about 160 Ω and roughly 42% spin polarization.

West Virginia University, in partnership with the University of Delaware, has been awarded a four-year, $4 million grant from the National Science Foundation's Established Program to Stimulate Competitive Research (NSF EPSCoR) to develop magnetic materials that can be switched using electrical pulses alone, without an applied magnetic field. The project, titled "Spin Control via Topology, Symmetry and Dimensionality," is led by WVU physicist Mikel Holcomb, with UD co-principal investigator Ryan Comes and colleagues Joshua Zide and John Xiao; UD's share of the award comes to close to $1.4 million.

Magnetic materials already anchor widely used memory technologies such as hard drives, but changing their magnetic state normally requires generating a magnetic field, a comparatively energy-hungry and hard-to-miniaturize approach. Controlling magnetism directly with electricity instead, by manipulating electron spin, could enable more energy-efficient memory and tighter integration of magnetic storage with conventional electronics, one of the central goals driving spintronics research.

Researchers at Boston College, University of Chemistry and Technology Prague and Japan's National Institute for Materials Science have built a spin transistor that can be switched either electrically or magnetically from within a single two-dimensional device, using the van der Waals magnetic semiconductor chromium sulfur bromide (CrSBr). The device reaches an electrical on/off ratio of a million percent and a magnetic on/off ratio of 3,000 percent, which the team says is well above what prior spin-transistor efforts have achieved.

The work targets the "von Neumann bottleneck": the energy and speed cost of continually shuttling data, including the billions of parameters in large AI models, between separate compute and memory blocks on a chip. A long-standing goal in spintronics is a single "spin transistor" device that combines a magnetic bit with a semiconducting switch, so it can compute and store data at once. Historically, building one has meant physically joining two different materials, a magnet and a semiconductor, together. "By engineering a single van der Waals crystal, CrSBr, that inherently possesses both semiconducting and magnetic properties, we eliminate losses at interfaces entirely," said Zdeněk Sofer, a materials-synthesis specialist at the University of Chemistry and Technology Prague.