Buhrman joined the faculty in 1973 after completing his doctoral degree. At Cornell, he is associated with the Materials Science Center, the Semiconductor Research Corporation’s Program in Microstructure Science and Technology, and the Cornell Nanofabrication Facility (CNF). He was the CNF’s associate director from 1981 through 1983, and is currently the chairman of its executive committee. In 1993 he was named the John Edson Sweet Professor of Engineering.  Buhrman has served on various national committees and advisory boards, and is active as a consultant in the area of applied physics. He is a fellow of the American Academy of Arts and Sciences, fellow of the American Physical Society, and a member of the Materials Research Society.

Research Interests

Our research program is concerned with the study of the magnetic, electronic and structural properties of nanostructures and thin-film systems with which we can address and resolve current problems in both basic and applied condensed-matter physics. A particular focus is on the study, control and utilization of the physical properties of materials at the nanoscale. Our research strategy involves the application of a wide range of experimental approaches. These include: the utilization of new approaches in electron-transport studies in thin film nanostructures; the nanofabrication and study of unique thin-film structures and devices; the development and application of ultrahigh-vacuum (UHV) instrumentation and techniques, including scanning tunneling microscopy and related ballistic electron microscopy techniques for surface and interface studies. Our program heavily utilizes the capabilities of the Cornell Nanofabrication Facility, and is associated with both the Center for Nanoscale Systems and the Cornell Center for Materials Research.  

Nanomagnetics and spin electronics: Our major thrust in this area currently is concerned with the phenomena of “spin-torque” where a spin-polarized current can, for example, be employed to excite or switch the orientation of a thin film nanomagnet through which it flows by the transfer of spin angular momentum from the conduction electrons to the local moment of the nanomagnet. This discovery is providing a new opportunity for the study of a wide range of dynamic nanomagnetic phenomena that was previously inaccessible to investigation.  It provides a new approach for the magnetic storage of information at the nanoscale, and could result in a universal memory device - fast, dense and nonvolatile – that is compatible with integration with highly scaled, high performance Si nanoelectonics.  It could also lead to nanoscale microwave oscillators and mixers for signal processing and communications applications. A related effort is the application of a new, ballistic electron microscopy technique, based on the scanning tunneling microscope, which we have invented for the nanoscale imaging of the magnetic properties of thin ferromagnet films and nanostructures with unprecedented spatial resolution. Another project is the achievement of enhanced spin-polarized ballistic electron injection into semiconductor structures. Such spin-injection is essential to a range of semiconductor phenomena that are forming the foundation of a new type of “spintronics” science and technology.

Condensed Matter and Materials Physics at the Nanoscale: We have developed a range of advanced techniques and approaches for the production of nanostructures to address a wide range of problems in condensed matter physics. Current and planned efforts include the study of individual quantum defects, the study of interfacial spin-dependent electronic transport in ferromagnetic – semiconductor systems, and the examination of the electronic properties of composite systems that seek to combine different components of nanoscale dimensions to obtain new functionality or to answer fundamental materials physics questions. 

Advances in nanoscale science and technology also requires the development of a much higher level of understanding and control of the electronic and structure properties of materials at the nanometer and atomic scales than has previously been achieved. One topic of widespread importance is the behavior of tunnel barrier structures consisting of ultra-thin (~ 0.5 – 1 nm thick) insulator layers sandwiched between metallic electrodes.  For example, such tunnel junction structures when formed with superconducting electrodes result in Josephson junctions that represent one of the most promising approaches to solid-state quantum computing devices or qubits, while improved and robest magnetic tunnel junctions with such ultra-thin barriers are also essential for spin-torque memory applications and also as sensors in ultra-high density magnetic hard drives. We are currently pursuing a broad-based materials development effort, utilizing scanning tunneling microscopy, surface spectroscopy and transport measurements that are showing promise of providing the required improvements.

Some recent publications 

•  “Sidewall oxide effects on spin-torque- and magnetic-field-induced reversal characteristics of thin-film nanomagnets,” O. Ozatay, P. G. Gowtham, K. W. Tan, J. C. Read, K. A. Mkhoyan and M. G. Thomas, G. D. Fuchs, P. M. Braganca, E. M. Ryan, K. V. Thadani, J. Silcox, D. C. Ralph and R. A. Buhrman, Nature Materials 7, 567 (2008).
• “Measurement of the spin-transfer-torque vector in magnetic tunnel junctions,” Jack C. Sankey, Yong-Tao Cui, Jonathan Z. Sun, John C. Slonczewski, R. A. Buhrman and D. C. Ralph, Nature Physics 4, 67-71 (2008).
• “Magnetic vortex oscillator driven by d.c. spin-polarized current,” V. S. Pribiag, I. N. Krivorotov, G. D. Fuchs, O. Ozatay, J. C. Sankey, D. C. Ralph and R. A. Buhrman, Nature Physics, 3, 498 (2007).
• “Spin torque, tunnel-current spin polarization, and magnetoresistance in MgO magnetic tunnel junctions,” G.D. Fuchs, J.A. Katine, S.I. Kiselev, D. Mauri, K.S. Wooley, D.C. Ralph, and R.A. Buhrman, Phys Rev Lett. 96  (2006).
• I.N. Krivorotov, N.C. Emley, J.C. Sankey, S.I. Kiselev, D.C. Ralph, and R.A. Buhrman, Time-domain measurements of nanomagnet dynamics driven by spin-transfer torques. Science. 307(5707):  p. 228, 2005.
• “Reducing the critical current for short-pulse spin-transfer switching of nanomagnets,” P.M. Braganca, I.N. Krivorotov, O. Ozatay, A.G.F. Garcia, N.C. Emley, J.C. Sankey, D.C. Ralph, and R.A. Buhrman, Appl Phys Lett. 87(11): 2005.
• “Spin-transfer effects in nanoscale magnetic tunnel junctions,” G.D. Fuchs, N.C. Emley, I.N. Krivorotov, P.M. Braganca, E.M. Ryan, S.I. Kiselev, J.C. Sankey, D.C. Ralph, R.A. Buhrman, and J.A. Katine, Appl Phys Lett. 85, 1205 (2004)
• “Microwave oscillations of a nanomagnet driven by a spin-polarized current,” S.I. Kiselev, J.C. Sankey, I.N. Krivorotov, N.C. Emley, R.J. Schoelkopf, R.A. Buhrman, and D.C. Ralph, Nature. 425, 380 (2003).
• “Ultrathin aluminum oxide tunnel barriers,”     W.H. Rippard, A.C. Perrella, F.J. Albert, and R.A. Buhrman, Phys Rev Lett. 88  (2002).
• “Spintronics: A spin-based electronics vision for the future,” S.A. Wolf, D.D. Awschalom, R.A. Buhrman, J.M. Daughton, S. von Molnar, M.L. Roukes, A.Y. Chtchelkanova, and D.M. Treger, Science. 294, 1488 (2001). 
• “Current-driven magnetization reversal and spin-wave excitations in Co/Cu/Co pillars,“ J.A. Katine, F.J. Albert, R.A. Buhrman, E.B. Myers, and D.C. Ralph, Phys Rev Lett. 84, 3149 (2000).