Physics enabled by the discovery of spin-transfer torques

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].

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[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 Žutić, “Tunable magnetic textures: From Majorana bound states to braiding,” Solid State Communications 262, 1 (2017)