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The 2014 Magnetism Roadmap
Robert L. Stamps, Stephan Breitkreutz, Johan Åkerman, Andrii V. Chumak, YoshiChika Otani, Gerrit E. W. Bauer, Jan-Ulrich Thiele, Martin Bowen, Sara A. Majetich, Mathias Kläui, Ioan Lucian Prejbeanu, Bernard Dieny, Nora M. Dempsey, Burkard Hillebrands
TL;DR
The roadmap surveys selected active developments in modern magnetism, emphasizing nano-magnetic phenomena, interfaces, materials, and applications while recognizing that it is not comprehensive. It synthesizes directions including magnon spintronics, organic spin electronics, magnetic random-access memory, and biomedical uses, highlighting both demonstrated capabilities and unresolved challenges. Across these areas, progress depends on stronger materials, device architectures, experimental validation, and technological maturity.
Problem
The roadmap addresses the need to organize current and future challenges across selected emerging magnetic phenomena, materials, and applications rather than provide a complete field review.
Method
The paper presents a multi-section expert roadmap surveying selected developments in nano-magnetism, interfaces, materials, devices, and biotechnology.
Results
The roadmap identifies demonstrated magnonic logic and conversion concepts, organic spin-injection opportunities, MRAM development paths, and biomedical uses of magnetic particles alongside unresolved integration and validation challenges.
Takeaways & Limitations
Future progress requires integrated magnonic circuits, better organic materials and interfaces, improved MRAM maturity, and continued development of magnetic technologies for applications.
Takeaways & Limitations
The roadmap is selective rather than comprehensive, and several covered technologies remain constrained by unresolved mechanisms, variability, or incomplete material-property combinations.
Abstract
from arXiv · showhide
Magnetism is a very fascinating and dynamic field. Especially in the last 30 years it has experienced many major advances in the full range from novel fundamental phenomena to new products. Applications such as hard disk drives and magnetic sensors are part of our daily life, and new applications, such as in non-volatile computer random access memory, are expected to surface shortly. Thus it is timely for describing the current status, and current and future challenges in the form of a Roadmap article. This 2014 Magnetism Roadmap provides a view on several selected, currently very active innovative developments. It consists of 12 sections, each written by an expert in the field and addressing a specific subject, with strong emphasize on future potential. This Roadmap cannot cover the entire field. We have selected several highly relevant areas without attempting to provide a full review - a future update will have room for more topics. The scope covers mostly nano-magnetic phenomena and applications, where surfaces and interfaces provide additional functionality. New developments in fundamental topics such as interacting nano-elements, novel magnon-based spintronics concepts, spin-orbit torques and spin-caloric phenomena are addressed. New materials, such as organic magnetic materials and permanent magnets are covered. New applications are presented such as nano-magnetic logic, non-local and domain-wall based devices, heat-assisted magnetic recording, magnetic random access memory, and applications in biotechnology. May the Roadmap serve as a guideline for future emerging research directions in modern magnetism.
Magnon spintronics Andrii Chumak, University of Kaiserslautern
Magnon spintronics uses magnons to transport and process spin information, combining conversion between electronic currents and magnon flows with wave-based and nonlinear processing. The field has demonstrated promising components but still requires integrated circuits and further materials development.
- Status: Magnons offer nanoscale information transport, GHz-to-THz operation, and wave-based processing concepts that differ from conventional CMOS approaches.Their linear and nonlinear properties support processing clusters of information rather than only individual bits.
- Current and Future Challenges: Promising directions include spin-pumping, spin-transfer-torque, and spin-Hall-effect conversion, low-damping materials such as Heusler compounds, and magnon Bose-Einstein condensation.Room-temperature magnon condensation has been reported at sufficiently high injected magnon density, while applications remain exploratory.
- Status: Magnon spintronics converts charge- and spin-currents into magnon flows, processes information in magnons, and converts it back.Magnon waves enable fast processing of complex data inputs.
- Digital data processing: Magnonics has demonstrated nonlinear manipulation of one magnon by another and an all-magnon transistor, but combining multiple logic elements remains unrealized.The paper identifies integrated magnonic circuits as an outstanding development step.
- Digital data processing: A proof-of-principle spin-wave XNOR gate uses DC-current-controlled phase shifts and interference in Mach-Zehnder waveguides to produce the output.The logical inputs are encoded as no current for “0” and a π-phase-shifting current for “1”.
Developing synergies between organic and spin electronics Martin Bowen, Institut de Physique et Chimie des Matériaux de Strasbourg, CNRS, University of Strasbourg
Organic and spin electronics may reinforce each other: spin-polarized currents could affect OLED recombination, while weak organic spin-orbit coupling may support long spin transport and coherence. The field remains promising but immature, with molecular functionality depending on a firmer understanding of transport and interfaces.
- Status: Spin-polarized currents are predicted to alter singlet-to-triplet recombination and potentially enhance organic light-emitting-device efficiency.This motivates combining organic electronics with spin-dependent transport.
- Status: Weak spin-orbit coupling in organic semiconductors is expected to promote long spin diffusion lengths and spin coherence times.These properties could support organic spintronics circuits.
- Status: Measurements of spin-polarized transport across approximately 100nm organic films demonstrate promise, but the mechanism remains controversial.Spin-polarized tunneling across organic barriers has addressed the resistivity-mismatch challenge for spin injection.
- Future potential: Future molecular spintronic devices could use organic magnetic semiconductors as electrodes or barriers and spin-crossover molecules to promote memristance.These possibilities depend on establishing a solid knowledge base for spintronics using simple molecules.
- Current and Future Challenges: The field’s central challenges are explaining magnetoresistance in thin organic layers and determining how spins remain coherent over long diffusion lengths and times.The section explicitly frames these as unresolved research questions.
1) How are spins injected into the OS?
Spin injection into organic semiconductors is constrained by uncertain transport mechanisms, structural disorder, interdiffusion, and interface limitations. The roadmap calls for more rigorous experiments, simpler injectors, improved interfaces, and systematic room-temperature device validation.
- How are spins injected into the OS?: A Co/MnPc interface exhibits 84% spin asymmetry at the Fermi level and 300K, with metallic adsorption predicting strongly spin-polarized current.The result motivates testing whether such interfaces can serve as practical spin-polarized current sources.
- How are spins injected into the OS?: The field needs systematic spectroscopy and transport studies for matched ferromagnet–molecule pairs, including tests of room-temperature tunneling magnetoresistance and molecular spin-crossover functionality.Reported tunneling magnetoresistance is presently 300–500% at 2K, while room-temperature performance remains an open question.
- How are spins injected into the OS?: Spin coherence in organic layers remains an explicit unresolved question alongside the injection problem.The roadmap asks how spins remain coherent over long diffusion lengths and times.
- How are spins injected into the OS?: Organic magnetoresistance remains compatible with multiple mechanisms, including electron-hole interactions, triplet excitons, polarons, bipolarons, and spin-orbit coupling.Current data does not readily distinguish among these explanations.
- How are spins injected into the OS?: Metal deposition can cause substantial interdiffusion into organic layers, making structural quality and interface formation central experimental concerns.Avoiding interdiffusion could clarify organic magnetoresistance, though potentially at the expense of spinterface properties.
- How are spins injected into the OS?: Structural disorder causes hopping through localized states, complicating interpretation of diffusive spin transport in organic thin films.Improved film and interface structure, together with a definition of reasonable ordering, is needed for clearer results.
- How are spins injected into the OS?: Ferromagnetic oxide electrodes such as LSMO are widely used for organic deposition compatibility but are not amenable to industrial applications because they do not work at room temperature.This creates a practical boundary for translating current device structures into industrial technology.
- How are spins injected into the OS?: Simpler 3d transition-metal injectors and oxidation-mitigation strategies, potentially using graphene, are proposed to improve room-temperature spin-injection understanding and integration.Graphene’s ability to impede ferromagnetic-surface oxidation is identified as potentially crucial for industrial spinterfaces.
Concluding Remarks –
Monodomain magnetic particles have well-understood forces, fields, and energy dissipation, supporting their use in biomedicine. They serve both diagnostic and therapeutic roles and enable fundamental biomedical investigations.
- Concluding Remarks –: Monodomain magnetic particles have well-understood forces, fields, and energy dissipation, enabling biomedical diagnosis, treatment, and fundamental research.Their established magnetic behavior supports these biomedical uses.
MRAM: status and roadmap I.L.Prejbeanu, B.Dieny, Spintec
MRAM is advancing toward denser, scalable nonvolatile memory through spintronic switching schemes and new cell architectures. Remaining challenges include sub-20nm maturity, variability, TMR, temperature range, and power consumption.
- Status: On-chip memory demand is driving integration of nonvolatility across the memory hierarchy toward normally-off, instant-on, and logic-in-memory architectures.The goal is to reduce static power while narrowing the processor–memory performance gap.
- Status: MRAM cells use magnetic tunnel junctions, while architectures exploit field writing, thermal assistance, STT, domain-wall propagation, or SOT.The roadmap surveys multiple architectures shown in Fig. 2 and identifies spintronics advances enabling their evolution.
- Challenges: Voltage or thermal assistance can reduce switching barriers and help balance writability, retention, and energy consumption in STT-based devices.Voltage-controlled devices could achieve lower power if they operate below approximately 1V.
- Challenges: Sub-20nm MRAM remains immature, with cell-to-cell variability, TMR amplitude, and temperature range still limiting technology development.Patterning-related edge defects and MgO damage locally alter barrier resistance, TMR, and magnetic anisotropy.
- Roadmap: Heusler and X1-xMnx alloys show potential for p-STTRAM, and the roadmap projects that Gb STTRAM requirements could be reached at the 12nm node.No existing alloy yet combines all required properties, including low magnetization, perpendicular anisotropy, and low damping.
- Roadmap: STTRAM may scale to approximately 10nm, while combining assisted switching with STT offers a route toward ultimate scalability.SOT-MRAM is presented as promising for nonvolatile logic and improved endurance, but present STT write energy remains far above the retention barrier.