Title: Physics enabled by the discovery of spin-transfer torques 

Speaker:Prof. Andrew Kent（New York University） 

Time: May 23, 2018 10:00AM

Venue: No. 303 meeting room of building 2, IOS, CAS

Abstract:
The magnetization of a magnetic material can be reversed by using electric currents that transport spin angular momentum [1]. This was predicted in magnetic tunnel junctions—two metallic ferromagnetic layers separated by a thin insulating barrier—by John Slonczewski in 1989 and demonstrated experimentally about a decade later. This discovery has had an enormous impact on magnetism research and technology [2], as prior to this the primary means to reorient the magnetization of a magnet was by applying magnetic fields (dating to 1819 and Oersted!). In this talk I will highlight some of the new physics enabled by the discovery of spin-transfer torques. This includes recent experiments in my group to create localized spin-wave excitations (magnons) in thin films with uniaxial magnetic anisotropy [3]. Spin-transfer torques also permit study of magnetic analogues of superconductivity, superfluidity and the Josephson effect that promise to increase our understanding of collective quantum effects. They may even enable braiding Majorana fermions [4].

[1] A. Brataas, A. D. Kent and H. Ohno, “Current-Induced Torques in Magnetic Materials”, Nature Materials 11, 372 (2012)
[2] A. D. Kent and D. C. Worledge, “A new spin on magnetic memories,” Nature Nanotechnology 10, 187 (2015)
[3] D. Backes, F. Macia, S. Bonetti, R. Kukreja, H. Ohldag and A. D. Kent, “Direct Observation of a Localized Magnetic Soliton in a Spin-Transfer Nanocontact,” PRL 115, 127205 (2015)
[4] Alex Matos-Abiaguea, Javad Shabani, Andrew D. Kent, Geoffrey L. Fatina, Benedikt Scharfa, Igor Z?utic?, “Tunable magnetic textures: From Majorana bound states to braiding,” Solid State Communications 262, 1 (2017)

Biography：Andrew Kent is a Professor of Physics at New York University. He received his Ph.D. from Stanford University in 1988 and conducted post-doctoral research at the University of Geneva in Switzerland and the IBM T. J. Watson Research Center. His research interests are in the physics of magnetic nanostructures, nanomagnetic devices and magnetic information storage. He has conducted experimental studies of quantum tunneling of magnetization and coherence in arrays of nanometer scale magnets known as single molecule magnets. He has also studied spin-dependent transport and spin momentum transfer in thin film magnetic nanopillars. Kent has expertise in thin film growth and characterization, device nanofabrication and high frequency measurements including, ferromagnetic resonance, electron paramagnetic resonance and time-resolved studies of magnetization dynamics. In 2007 he founded Spin-Transfer Technologies, a startup company developing spin torque magnetic random access memory devices. Kent is a fellow of the American Physical Society (APS), has served as chair of APS topical group on magnetism and its applications (GMAG) and is an advisory board member of the Committee of Concerned Scientists. He is on the executive committee of the APS Division of Condensed Matter Physics (DCMP) and Program Co-Chair of the 58th Annual Magnetism and Magnetic Materials conference (MMM 2013). Kent accomplishments were recognized by an Honorary Doctorate from the University of Lorraine (“Docteur Honoris Causa” de l'Universite de Lorraine), in September 2013.