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Ralph, Daniel C
Horace White Professor of Physics
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Positions
- Professor, Physics (PHYS), College of Arts and Sciences
- Director, Cornell NanoScale Science and Technology Facility (CNF), Office of the Vice Provost for Research
Research Areas
- condensed matter physics and materials science
- experimental condensed-matter physics
- nanoscience and nanobiotechnology
Websites
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- Research
- Publications
- Teaching
- Background
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Affiliations
member of graduate field
other Cornell affiliations
Research
research overview
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- New nanofabrication techniques
- Electronic properties on molecular length scales
- High-speed dynamics in magnetic devices
- Correlated-electron states in magnets and superconductors
- Quantum properties of defects and impurities
principal investigator on
- CURRENT-INDUCED TORQUES IN FERROMAGNETIC STRUCTURES awarded by NATL SCIENCE FOUNDATION 2010 - 2014
- ELECTRICAL CONTROL OF MAGNETIC DYNAMICS IN HYBRID METAL-SEMICONDUCTOR SYSTEMS awarded by ARMY RESEARCH OFFICE 2008 - 2013
- FITT: DEVELOPMENT OF A LOW VOLTAGE, LOW POWER TRANSISTOR BASED ON TOPOLOGICAL SURFACE STATES. awarded by SPACE AND NAVAL WARFARE SYSTEMS CENTER SAN DIEGO 2011 - 2013
- IRES-INTERNATIONAL RESEARCH EXPERIENCE IN NANOTECHNOLOGY-NNIN AND NIMS 2010 awarded by NATL SCIENCE FOUNDATION 2010 - 2013
- MATCHING FUNDS FOR THE CORNELL NANOSCALE SCIENCE AND TECHNOLOGY FACILITY PART OF NNIN awarded by NYS SCIENCE, TECHNOLOGY AND ACADEMIC RESEARCH 2009 - 2014
- NNIN: NATIONAL NANOTECHNOLOGY INFRASTRUCTURE NETWORK awarded by NATL SCIENCE FOUNDATION 2004 - 2014
- NNIN: NATIONAL NANOTECHNOLOGY INFRASTRUCTURE NETWORK CAP EQUIP ONLY: ARRA FUNDS awarded by NATL SCIENCE FOUNDATION 2009 - 2014
co-principal investigator on
- CORNELL CENTER FOR MATERIALS RESEARCH - MRSEC awarded by DIRECTORATE FOR ENGINEERING NSF 2011 - 2017
Publications
individual publications
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academic article
- Current-Induced Switching of Perpendicularly Magnetized Magnetic Layers Using Spin Torque From the Spin Hall Effect. Physical Review Letters. 109:096602-096607. 2012
- Magnetic oscillations driven by the spin Hall effect in 3-terminal magnetic tunnel junction devices. Physical Review Letters. 109:186602-186607. 2012
- Network Analyzer Measurements of Spin Transfer Torques in Magnetic Tunnel Junctions. Applied Physics Letters. 101:022417-022421. 2012
- Phase Locking and Frequency Doubling in Spin-Transfer-Torque Oscillators With Two Coupled Free Layers. Physical Review B. 86:060411. 2012
- Resonance Measurement of Nonlocal Spin Torque in a Three-Terminal Magnetic Device. Physical Review Letters. 108:147201-147205. 2012
- Spin torque switching with the giant spin Hall effect of tantalum. Science. 336:555-558. 2012
- Spin transfer torque devices utilizing the giant spin Hall effect of tungsten. Applied Physics Letters. 101:122404-122408. 2012
- Plasmon Resonance in Individual Nanogap Electrodes Studied Using Graphene Nanoconstrictions as Photodetectors. Nano Letters. 11:1814-1818. 2011
- Spin-torque ferromagnetic resonance induced by the spin hall effect. Physical Review Letters. 106. 2011
- Conditions for microwave amplification due to spin-torque dynamics in magnetic tunnel junctions. Applied Physics Letters. 99:022505-022508. 2011
- Images of a Spin-Torque-Driven Magnetic Nano-Oscillator. Physical Review Letters. 106:167202-167206. 2011
- Spin-torque ferromagnetic resonance induced by the spin hall effect. Physical Review Letters. 106:036601. 2011
- Spin-torque-driven ballistic precessional switching with 50 ps impulses. Applied Physics Letters. 99:102507-102510. 2011
- Spin-transfer torque in nanoscale magnetic devices. Philosophical Transactions of the Royal Society. 369:3617-3630. 2011
- Time-resolved measurement of spin-transfer-driven ferromagnetic resonance and spin torque in magnetic tunnel junctions. Nature Physics. 7:496-501. 2011
- Tunnel magnetoresistance and spin torque switching in MgO-based magnetic tunnel junctions with a Co/Ni multilayer electrode. Applied Physics Letters. 97. 2010
- Single-shot time-domain studies of spin-torque-driven switching in magnetic tunnel junctions. Physical Review Letters. 104. 2010
- Single-shot time-domain studies of spin-torque-drivien switching in magnetic tunnel junctions. Physical Review Letters. 104:097201. 2010
- Tunnel magnetoresistance and spin torque switching in MgO-based magnetic tunnel junctions with a Co/Ni multilayer electrode. Applied Phyics Letters. 97:072513. 2010
- Tunnel magnetoresistance and spin torque switching in MgO-based magnetic tunnel junctions with a Co/Ni multilayer electrode. Applied Physics Letters. 97:072513. 2010
- Long-timescale fluctuations in zero-field magnetic vortex oscillations driven by dc spin-polarized current. Physical Review B. 80. 2009
- Bias and angular dependence of spin-transfer torque in magnetic tunnel junctions. Physical Review B. 79:224416-224426. 2009
- Long-timescale fluctuations in zero-field magnetic vortex oscillations driven by dc spin-polarized current. Physical Review B. 80:180411-180415. 2009
- Reduction of the spin-torque critical current by partially canceling the free layer demagnetization field. Applied Physics Letters. 94:122508-122511. 2009
- Sensitivity of spin-torque diodes for frequency-tunable resonant microwave detection. Journal of Applied Physics. 106:053905-053906. 2009
- Ultrafast switching of a nanomagnet by a combined out-of-plane and in-plane polarized spin current pulse. Applied Physics Letters. 95:012506-012509. 2009
- Resonant spin-transfer-driven switching of magnetic devices assisted by microwave current pulses. Physical Review B. 77:214440-214447. 2008
- Sidewall Oxide Effects on Spin-Torque and Magnetic-Field-Induced Reversal Characteristics of Thin-Film Nanomagnets. Nature Materials. 7:567-573. 2008
- Sidewall oxide effects on spin-torque- and magnetic-field-induced reversal characteristics of thin-film nanomagnets. Nature Materials. 7:567-573. 2008
- Strong linewidth variation for spin-torque nano-oscillators as a function of in-plane magnetic field angle. Physical Review B. 78:024409-024416. 2008
- Phonons and conduction in molecular quantum dots: Density functional calculations of Franck-Condon emission rates for bifullerenes in external fields. Physical Review B. 76. 2007
- Large-amplitude coherent spin waves excited by spin-polarized current in nanoscale spin valves. Physical Review B. 76:024418-024432. 2007
- Magnetic Vortex Oscillator Drive by D.C. Spin-Polarized Current. Nature Physics. 3:498-503. 2007
- Magnetic Vortex Oscillator Drive by D.C. Spin-Polarized Current. Nature Physics. 3:498-503. 2007
- Spin-Torque Ferromagnetic Resonance Measurements of Damping in Nanomagnets. Applied Physics Letters. 91:062507-062510. 2007
- Spin Torque, Tunnel-Current Spin Polarization, and Magnetoresistance in MgO Magnetic Tunnel Junctions. Physical Review Letters. 96:186603-186607. 2006
- Spin transfer by nonuniform current injection into a nanomagnet. Applied Physics Letters. 88:202502-202505. 2006
- Vibration-Assisted Electron Tunneling in C140 Transistors. Nano Letters. 5:203-207. 2005
- Adjustable spin torque in magnetic tunnel junctions with two fixed layers. Applied Physics Letters. 86:152509-152512. 2005
- Spin-Transfer Effects in Nanoscale Magnetic Tunnel Junctions. Applied Physics Letters. 85:1205. 2004
- Wiring up single molecules. Thin Solid Films. 438-439:457-461. 2003
- Calculation of Quantum Tunneling for a Spatially Extended Defect: The Dislocation Kink in Copper Has a Low Effective Mass. Physical Review Letters. 86. 2001
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article
- Coupling of spin and orbital motion of electrons in carbon nanotubes. Nature. 452:448-452. 2008
- The Kondo Effect in the Presence of Ferromagnetism. Science. 306:86-89. 2004
- Coulomb blockade and the Kondo effect in single-atom transistors. Nature. 417:722-725. 2002
selected publications listing
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- 2008
- Strong linewidth variation for spin-torque nano-oscillators as a function of in-plane magnetic field angle.
K. V. Thadani, G. Finocchio, Z.-P. Li, O. Ozatay, J. C. Sankey, I. N. Krivorotov, Y.-T. Cui, R. A. Buhrman, and D. C. Ralph, Phys. Rev. B 78, 024409 (2008). - Resonant spin-transfer-driven switching of magnetic devices assisted by microwave current pulses.
Y.-T. Cui, J. C. Sankey, C. Wang, K. V. Thadani, Z.-P. Li, R. A. Buhrman, and D. C. Ralph, Phys. Rev. B 77, 214440 (2008). - 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, 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) and Supplementary Info. - Enhancement in spin-torque efficiency by nonuniform spin current generated within a tapered nanopillar spin valve.
P. M. Braganca, O. Ozatay, A. G. F. Garcia, O. J. Lee, D. C. Ralph, and R. A. Buhrman, Phys. Rev. B 77, 144423 (2008). - Coupling of Spin and Orbital Motion of Electrons in Carbon Nanotubes.
F. Kuemmeth, S. Ilani, D. C. Ralph, and P. L. McEuen, Nature 452, 449 (2008) and Supplementary Info.
(See accompanying News & Views and the Nature Physics News & Views.) - Current Persectives: Spin Transfer Torques.
D. C. Ralph and M. D. Stiles, J. Magn. Magn. Mater. 320, 1190 (2008). - Current Persectives: Magnetoresistance and spin-transfer torque in magnetic tunnel junctions.
J. Z. Sun and D. C. Ralph, J. Magn. Magn. Mater. 320, 1227 (2008). - Time-domain studies of very-large-angle magnetization dynamics excited by spin transfer torques.
I. N. Krivorotov, N. C. Emley, R. A. Buhrman, and D. C. Ralph, Phys. Rev. B 77, 054440 (2008). - Measurement of the spin-transfer-torque vector in magnetic tunnel junctions.
J. C. Sankey, Y.-T. Cui, J. Z. Sun, J. C. Slonczewski, R. A. Buhrman, and D. C. Ralph, Nature Physics 4, 67 (2008) and Supplementary Info.
(See accompanying News & Views.)
2007
- Temperature dependence of anisotropic magnetoresistance and atomic rearrangements in ferromagnetic metal break junctions.
S.-F. Shi, K. I. Bolotin, F. Kuemmeth, and D. C. Ralph, Phys. Rev. B 76, 184438 (2007). - Magnetization reversal driven by spin-polarized current in exchange-biased nanoscale spin valves.
G. Finocchio, I. N. Krivorotov, L. Torres, R. A. Buhrman, D. C. Ralph, and B. Azzerboni, Phys. Rev. B 76, 174408 (2007). - Correspondence: Atomic motion in ferromagnetic break junctions.
S.-F. Shi and D. C. Ralph, Nature Nanotechnology 2, 522 (2007). - Spin-torque ferromagnetic resonance measurements of damping in nanomagnets.
G. D. Fuchs, J. C. Sankey, V. S. Pribiag, L. Qian, P. M. Braganca, A. G. F. Garcia, E. M. Ryan, Z.-P. Li, O. Ozatay, D. C. Ralph, and R. A. Buhrman, Appl. Phys. Lett. 91, 062507 (2007). - Phonons and conduction in molecular quantum dots: Density functional calculations of Franck-Condon emission rates for bifullerenes in external fields.
C. T. Chang, J. P. Sethna, A. N. Pasupathy, J. Park, D. C. Ralph, and P. L. McEuen, Phys. Rev. B 76, 045435 (2007). - Tuning the Kondo Effect with a Mechanically Controllable Break Junction.
J. J. Parks, A. R. Champagne, G. R. Hutchison, S. Flores-Torres, H. D. Abruña, and D. C. Ralph, Phys. Rev. Lett. 99, 026601 (2007).
(See accompanying Nature Nanotechnology Research Highlight -- pdf.) - Large-amplitude coherent spin waves excited by spin-polarized current in nanoscale spin valves.
I. N. Krivorotov, D. V. Berkov, N. L. Gorn, N. C. Emley, J. C. Sankey, D. C. Ralph, and R. A. Buhrman, Phys. Rev. B 76, 024418 (2007). - Magnetic vortex oscillator driven by d.c. spin-polarized current.
V. S. Pribiag, I. N. Krivorotov, G. D. Fuchs, P. M. Braganca, O. Ozatay, J. C. Sankey, D. C. Ralph, and R. A. Buhrman, Nature Physics 3, 498 (2007). - Kondo effect in single-molecule spintronic devices.
J. Martinek, L. Bordad, Y. Utsumi, J. König, J. von Delft, D. C. Ralph, G. Schön, and S. Maekawa, J. Magn. Magn. Mater. 310, e343 (2007). - Imaging Electromigration during the Formation of Break Junctions.
T. Taychatanapat, K. I. Bolotin, F. Kuemmeth, and D. C. Ralph, Nano Lett. 7, 652 (2007). Accompanying movies: Movie 01a, Movie 01b, Movie 02a, Movie 02b, Movie 03, Movie 04, Movie 05, Movie 06.
2006
- Anisotropic Magnetoresistance and Anisotropic Tunneling Magnetoresistance due to Quantum Interference in Ferromagnetic Metal Break Junctions.
K. I. Bolotin, F. Kuemmeth, and D. C. Ralph, Phys. Rev. Lett. 97, 127202 (2006). - Signatures of molecular magnetism in single-molecule transport spectroscopy.
M. H. Jo, J. E. Grose, K. Baheti, M. M. Deshmukh, J. J. Sokol, E. M. Rumberger, D. N. Hendrickson, J. R. Long, H. Park, and D. C. Ralph, Nano Lett. 6, 2014 (2006). - Time-Resolved Spin-Torque Switching and Enhanced Damping in Permalloy/Cu/Permalloy Spin-Valve Nanopillars.
N. C. Emley, I. N. Krivorotov, O. Ozatay, A. G. F. Garcia, J. C. Sankey, D. C. Ralph, and R. A. Buhrman, Phys. Rev. Lett. 96, 247204 (2006). - Spin-Transfer-Driven Ferromagnetic Resonance of Individual Nanomagnets.
J. C. Sankey, P. M. Braganca, A. G. F. Garcia, I. N. Krivorotov, R. A. Buhrman, and D. C. Ralph, Phys. Rev. Lett. 96, 227601 (2006) and supporting EPAPS document.
(See accompanying Nature Nanotechnology Research Highlight -- pdf.) - Spin transfer by nonuniform current injection into a nanomagnet.
O. Ozatay, N. C. Emley, P. M. Braganca, A. G. F. Garcia, G. D. Fuchs, I. N. Krivorotov, R. A. Buhrman, and D. C. Ralph, Appl. Phys. Lett. 88, 202502 (2006). - 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, 186603 (2006). - Electrochemical properties of self-assembled monolayers of polyaniline: Effects of the thiol substituent and reduced dimensionality.
B. Ulgut, Y. Zhao, J. E. Grose, D. C. Ralph, and H. D. Abruña, Langmuir 22, 4433 (2006). - From ballistic transport to tunneling in electromigrated ferromagnetic breakjunctions.
K. I. Bolotin, F. Kuemmeth, A. N. Pasupathy, and D. C. Ralph, Nano Lett. 6, 123 (2006).
2005
- Mechanisms limiting the coherence time of spontaneous magnetic oscillations driven by DC spin-polarized currents.
J. C. Sankey, I. N. Krivorotov, S. I Kiselev, P. M. Braganca, N.C. Emley, R. A. Buhrman, and D. C. Ralph, Phys. Rev. B 72 , 224427 (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, 112507 (2005). - Spin-transfer excitations of permalloy nanopillars for large applied currents.
S. I. Kiselev, J. C. Sankey, I. N. Krivorotov, N.C. Emley, R. A. Buhrman, and D. C. Ralph, Phys. Rev. B 72 , 064430 (2005) - Adjustable spin torque in magnetic tunnel junctions with two fixed layers.
G. D. Fuchs, I. N. Krivorotov, P. M. Braganca, N. C. Emley, A. G. F. Garcia, D. C. Ralph, and R. A. Buhrman, Appl. Phys. Lett. 86, 152509 (2005). - Mechanically-adjustable and electrically-gated single-molecule transistors.
A. R. Champagne, A. N. Pasupathy, and D. C. Ralph, Nano Lett. 5, 305 (2005). - Vibration-assisted electron tunneling in C140 single-molecule transistors.
A. N. Pasupathy, J. Park, C. Chang, A. V. Soldatov, S. Lebedkin, R. C. Bialczak, J. E. Grose, L. A. K. Donev, J. P. Sethna, D. C. Ralph, and Paul. L. McEuen, Nano Lett. 5, 203 (2005). - Transistor behavior via Au clusters etched from electrodes in an acidic gating solution: Metal nanoparticles mimicking conducting polymers.
J. E. Grose, A. N. Pasupathy, D. C. Ralph, B. Ulgut, and H. D. Abruña, Phys. Rev. B 71, 035306 (2005). - Time-Domain Measurements of Nanomagnet Dynamics Driven by Spin-Transfer Torques.
I. N. Krivorotov, N. C. Emley, J. C. Sankey, S. I. Kiselev, D. C. Ralph, and R. A. Buhrman, Science 307, 228 (2005) and Supplementary Info.
(See accompanying Perspective.)
2004
- Temperature dependence of spin-transfer-induced switching of nanomagnets.
I. N. Krivorotov, N. C. Emley, A. G. F. Garcia, J. C. Sankey, S. I. Kiselev, D. C. Ralph and R. A. Buhrman, Phys. Rev. Lett. 93, 166603 (2004). - The Kondo effect in the presence of ferromagnetism.
A. N. Pasupathy, R. C. Bialczak, J. Martinek, J. E. Grose, L. A. K. Donev, P. L. McEuen, and D. C. Ralph, Science 306, 86 (2004)
(See accompanying Perspective.) - Spin-dependent transport in molecular tunnel junctions.
J. R. Petta, S. K. Slater, and D. C. Ralph, Phys. Rev. Lett. 93, 136601 (2004). - 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). - Current-Induced Nanomagnet Dynamics for Magnetic Fields Perpendicular to the Sample Plane. S. I. Kiselev, J. C. Sankey, I. N. Krivorotov, N. C. Emley, M. Rinkoski, C. Perez, R. A. Buhrman, and D. C. Ralph, Phys. Rev. Lett. 93, 036601 (2004).
- Reduction of spin transfer by synthetic antiferromagnets.
N. C. Emley, F. J. Albert, E. M. Ryan, I. N. Krivorotov, D. C. Ralph, R. A. Buhrman, J. M. Daughton, and A. Jander, Appl. Phys. Lett. 84, 4257 (2004). - Metal-nanoparticle single-electron transistors fabricated using electromigration.
K. I. Bolotin, F. Kuemmeth, A. N. Pasupathy, and D. C. Ralph, Appl. Phys. Lett. 84, 3154 (2004).
2003
- 30 nm Channel Length Pentacene Transistors.
Y. Zhang, J. R. Petta, S. Ambily, Y. Shen, G. G. Malliaras, and D. C. Ralph, Adv. Mater. 15, 1632 (2003). - 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).
(See accompanying News & Views.) - Wiring up single molecules.
J. Park, A. N. Pasupathy, J. I. Goldsmith, A. V. Soldatov, C. Chang, Y. Yaish, J. P. Sethna, H. D. Abruña, D. C. Ralph, and P. L. McEuen, Thin Sol. Films 438, 457 (2003). - Nanometer-scale Scanning Sensors Fabricated Using Stencil Lithography.
A. R. Champagne, A. J. Couture, F. Kuemmeth, and D. C. Ralph, Appl. Phys. Lett. 82, 1111 (2003).
- Strong linewidth variation for spin-torque nano-oscillators as a function of in-plane magnetic field angle.
featured in archived article
speaker at Cornell event
Teaching
teaching activities
Background
education and training
- Ph.D. in Physics, Cornell University 1993
- B.S. in Physics and Mathematics, Vanderbilt University 1986
awards and distinctions listing
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- Alfred P. Sloan Fellow, 1996-99
- David and Lucile Packard Foundation Fellow, 1997-2002
- William L. McMillan Award, 1997.
- Research Corporation Research Innovation Award, 1997.
- ONR Young Investigators Award, 1997-2000.
- Provost's Award for Distinguished Scholarship, 2003.