Two NRL Research Physicists Named APS Fellows

4/5/2004 - 21-04w
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Two Naval Research Laboratory scientists have recently been elected fellows in the American Physical Society (APS). The APS Fellowship Program was created to recognize members who have made advances in knowledge through original research and publication or made significant and innovative contributions in the application of physics to science and technology. Each year, no more than one-half of one percent of the then current membership of the Society are recognized by their peers for election to the status of Fellow.

Dr. Mark Johnson, a research physicist at NRL, was recognized "for his pioneering achievement demonstrating electrical spin injection and detection in ferromagnetic - nonmagnetic - ferromagnetic metal structures, and discovering long conduction electron spin diffusion lengths in bulk and thin film metals."

Dr. Johnson's research at NRL is both theoretical and experimental, and focuses on the electrical transport of spin polarized electrons in novel systems. This basic research involves the invention and development of nanometer scale device structures that incorporate a ferromagnetic element, and is a cornerstone of the new field known as "Spintronics" or "Magnetoelectronics." Dr. Johnson made early contributions to the development of nonvolatile Magnetic Random Access Memory (MRAM), which is the category of Spintronic devices that is closest to commercial realization. More recently, he has been working on spin-dependent transport in semiconductors. He discovered a novel technique for creating and measuring nonequilibrium spin magnetization in a class of high mobility semiconductor structures known as asymmetric quantum wells. He performed experiments that involved both electrical spin injection and electrical spin detection in a two-dimensional electron gas, including the first measurement of the spin-dependent mean free path in an indium arsenide single quantum well. In his ongoing work, Dr. Johnson is fabricating and studying novel device structures with dimensions of 100 nm and less.

Dr. Johnson received his A.B. in psychology and physics at the University of California at Santa Cruz and his M.S. and Ph.D. in physics form Cornell University. He worked as a postdoctoral associate at Cornell University from 1986 to 1987 and as a postdoctoral fellow at the University of California, Berkeley, from 1987 to 1989. Dr. Johnson was a visiting scientist at Stanford University from 1989 to 1990 and then became a Member of Technical Staff at Bellcore in 1990. Dr. Johnson came to NRL to work in the Materials Science and Technology Division in 1995.

Dr. Berend T. Jonker, also a research physicist at NRL, was recognized "for contributions to the field of magneto-electronics, including low dimensional magnetism in metals, spin-dependent carrier localization in semiconductors, and spin injection, scattering, and ferromagnetic order in semiconductor heterostructures."

Dr. Jonker's initial work at NRL focused on magnetic order in two-dimensional metal single crystal films. He was one of the first to conclude that reduced dimensionality resulted in a dominant perpendicular magnetic anisotropy and an out-of-plane magnetization, factors important in the design of nanoscale magnetic devices such as non-volatile memory.

His current research involves electrical injection of spin-polarized carriers from magnetic contacts into a semiconductor using the spin-polarized light emitting diode (NRL patent) as a test platform, with an emphasis on interface physics. Although charge transport is the basis for existing electronics, continued progress in circuit performance by reducing device dimensions (at a rate commonly referred to as Moore's law) is expected to be curtailed by practical and fundamental limits within 10 years. Consequently, there is keen interest in exploring new avenues and paradigms for future technologies. Since spin is also a fundamental property of an electron (in addition to charge), the use of carrier spin as a new degree of freedom in an electronic device represents one of the most promising candidates for this paradigm shift. This approach, referred to as "magneto-electronics" or "spintronics", offers new functionality as well as the potential for higher speed, low power operation of nanoscale devices [recent reviews may be found in references 1 and 2]. Dr. Jonker's research team has demonstrated substantial electrical spin injection into a semiconductor device (40-85%), and provided the first experimental identification of spin scattering defects at an interface within such a device. Recently, Dr. Jonker's group has addressed the physics of magnetic ordering in semiconductors, and discovered the first Group IV-based ferromagnetic semiconductor [3]. Such materials simultaneously exhibit semiconducting properties as well as long range ferromagnetic order, which are the twin cornerstones of modern information technology. Hence, there is keen interest in realizing these properties in a single material system which can be readily transitioned.

Dr. Jonker came to work at NRL as a National Research Council postdoctoral associate in 1984, and was hired as a research physicist in the Materials Science and Technology Division in 1986. He is currently Section Head of the Magnetoelectronic Materials and Devices section (Code 6361). He has also served as an adjunct professor at the State University of New York at Buffalo since 1995.

Dr. Jonker received his B.A. degree in physics from Calvin College, Grand Rapids, Michigan, in 1977, and his M.S. and Ph.D. degrees in physics from the University of Maryland in 1981 and 1983, respectively. He is a fellow of the American Vacuum Society, and has served as co-organizer for several international conferences on spintronics. He has received six Alan Berman Research Publication Awards, holds six patents, presented over 100 invited talks, authored one book chapter and co-authored over 150 refereed publications.

[1] B. T. Jonker, Proceedings of the IEEE, vol. 91, no. 5, pp. 727-740 (2003).
[2] B. T. Jonker, S. C. Erwin, A. Petrou and A. G. Petukhov, Materials Research Society Bulletin, vol. 28, no. 10, pp 740-748 (2003).
[3] Y. D. Park et al, Science 295, pp. 651-654 (2002).

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