Introduction to Technical Programs
Several of the Magnetics Group technical programs cut across projects. These programs include nanomagnetodynamics, spin electronics, scanned-probe microscopy, superconductor characterization, and standards.
Nanomagnetodynamics
The study of nanomagnetodynamics — high-frequency precession and damping of magnetization in films and devices below one micrometer in size — is undertaken in the Magnetodynamics Project, the Magnetic Thin Films and Devices Project, and the Nanoprobe Imaging Project, in collaboration with the Materials Science and Engineering Laboratory.
Advances in magnetic information storage are vital to economic growth and U.S. competitiveness in the world market for computer products and electronic devices. Key improvements needed are increases in data transfer rates during reading and writing, and increases in storage density in magnetic disk and tape media. Solid-state magnetic random-access memory will become a new factor in data storage. Future high-performance magnetic recording systems will have to write and read data in nanometric devices at rates exceeding 1 gigahertz, with corresponding magnetic switching times of less than 1 nanosecond.
Spin Electronics
Spin electronics is a new direction in electronics that promises to revolutionize telecommunications and information processing. Research in spintronics is conducted in the Magnetodynamics Project, the Magnetic Thin Films and Devices Project, and the Magnetic Recording Measurements Project.
Spin electronics is based on the manipulation and control of the quantum-mechanical spin of a semiconductor's charge carrier. Spintronics holds the promise of extending telecommunications frequencies into the terahertz regime. The frequency performance of devices based on charge transfer is limited by electron velocities, charge-transfer times, and carrier mobilities, whereas the electron spin has no fundamental frequency limitation, as long as coherence can be preserved.
Recent advances in spin-based semiconductor devices have demonstrated that coherent spin precession can be maintained for hundreds of microseconds. The precession frequency can be controlled by applied magnetic fields, gate voltages, and modulation doping techniques. We aim to develop new techniques to measure and control spin precession in small spin-based devices. The goal is to create and characterize precessing spin packets, consisting of one million spins, using high-speed electrical and optical techniques.
In addition to exploring spin dynamics in semiconductors, we are studying metallic devices that use spin-momentum transfer to induce coherent precession. Recent theoretical work predicts that a spin-polarized direct current injected into nanometric magnetic structures can generate coherent precession of the magnetization. The precession frequency can be tuned from 1 gigahertz to 50 gigahertz by changing the current amplitude or the polarization angle. Spin-polarized currents can switch small magnetic elements. We are working on using this effect as a source of precessing spins for semiconductor devices and as the basis for a novel spin amplifier.
Scanned-Probe Microscopy
We are developing scanned-probe microscopy in support of the magnetic data-storage industry, the microelectronics industry, and national security agencies of the government. Work is undertaken in the Magnetic Recording Measurements Project and the Nanoprobe Imaging Project.
We emphasize instrumentation for high-resolution imaging, and work with our collaborators to relate scanned-probe images to magnetic and electronic properties of recording media and electronic devices. Probes include giant-magnetoresistive devices and particles that undergo ferromagnetic resonance. Among the applications are the recovery of data from damaged recording media and certification of the authenticity of recorded media. Our goals include not only the qualitative imaging of materials but quantitative imaging of magnetic fields that have their sources in magnetic domains or current distributions.
Superconductor Characterization
We have a quarter-century history of making accurate measurements of — and developing the theory of measurement for — the electric, magnetic and mechanical properties of superconductor wires and tapes for power applications. This effort is centered in the Standards for Superconductor Characterization Project and the Superconductor Electromagnetic Measurements Project.
The properties we measure include critical-current density as a function of temperature and mechanical strain, residual resistivity ratio, and magnetic hysteresis loss. We investigate both high-temperature and conventional low-temperature superconductor compounds. The overarching theme of our work is to help establish best practices for superconductor characterization.
Standards
Activities undertaken by the Group include the development of both artifact standards for device calibration and consensus standards for measurement procedures. Standards work is undertaken by the Standards for Superconductor Characterization Project, the Magnetic Recording Measurements Project, the Magnetic Thin Films and Devices Project, the Nanoprobe Imaging Project, and by Group management staff.
Artifact standards — established or under development — include those for superconductor critical current, weak magnetic moments, and magnetic imaging. Several of our staff members are active in consensus-standards organizations — including the International Electrotechnical Commission, the Versailles Project on Advanced Materials and Standards, the American Society for Testing and Materials, the Institute of Electrical and Electronics Engineers, and the National Electronics Manufacturing Initiative — in the areas of superconductor measurements, magnetic measurements, and metric practice.