Enhanced spin–orbit torques by oxygen incorporation in tungsten films

The origin of spin–orbit torques, which are generated by the conversion of charge-to-spin currents in non-magnetic materials, is of considerable debate. One of the most interesting materials is tungsten, for which large spin–orbit torques have been found in thin films that are stabilized in the A15 (β-phase) structure. Here we report large spin Hall angles of up to approximately –0.5 by incorporating oxygen into tungsten. While the incorporation of oxygen into the tungsten films leads to significant changes in their microstructure and electrical resistivity, the large spin Hall angles measured are found to be remarkably insensitive to the oxygen-doping level (12–44%). The invariance of the spin Hall angle for higher oxygen concentrations with the bulk properties of the films suggests that the spin–orbit torques in this system may originate dominantly from the interface rather than from the interior of the films.

[1]  S. Bandiera,et al.  Perpendicular switching of a single ferromagnetic layer induced by in-plane current injection , 2011, Nature.

[2]  M. Stiles,et al.  Current induced torques and interfacial spin-orbit coupling: Semiclassical modeling , 2013, 1301.4513.

[3]  S. Maekawa,et al.  Electric manipulation of spin relaxation using the spin Hall effect. , 2008, Physical review letters.

[4]  D. Ralph,et al.  Spin-torque ferromagnetic resonance induced by the spin Hall effect. , 2010, Physical review letters.

[5]  D. A. Pesin,et al.  Quantum kinetic theory of current-induced torques in Rashba ferromagnets , 2012, 1201.0990.

[6]  Y. Mai,et al.  Influences of oxygen on the formation and stability of A15 β-W thin films , 2000 .

[7]  D. D. Awschalom,et al.  Observation of the Spin Hall Effect in Semiconductors , 2004, Science.

[8]  Hyunsoo Yang,et al.  Spin-orbit-torque engineering via oxygen manipulation. , 2015, Nature nanotechnology.

[9]  D. Ralph,et al.  Spin transfer torque devices utilizing the giant spin Hall effect of tungsten , 2012, 1208.1711.

[10]  D. Hesp,et al.  Cu(110)表面状態に及ぼすステップと規則的欠陥の影響 , 2013 .

[11]  Aurelien Manchon,et al.  Diffusive spin dynamics in ferromagnetic thin films with a Rashba interaction. , 2011, Physical review letters.

[12]  D. Ralph,et al.  Current-induced switching of perpendicularly magnetized magnetic layers using spin torque from the spin Hall effect. , 2012, Physical review letters.

[13]  E. Rashba,et al.  Properties of a 2D electron gas with lifted spectral degeneracy , 1984 .

[14]  Eiji Saitoh,et al.  Conversion of spin current into charge current at room temperature: Inverse spin-Hall effect , 2006 .

[15]  L. Buda-Prejbeanu,et al.  Fast current-induced domain-wall motion controlled by the Rashba effect. , 2011, Nature materials.

[16]  S. Parkin,et al.  Role of transparency of platinum–ferromagnet interfaces in determining the intrinsic magnitude of the spin Hall effect , 2015, 1504.07929.

[17]  R. Duine,et al.  Current-induced torques in textured Rashba ferromagnets , 2012, 1205.0653.

[18]  J. Solomon,et al.  Magnetron sputter deposition of A-15 and bcc crystal structure tungsten thin films , 1995 .

[19]  A. Brataas,et al.  Enhanced gilbert damping in thin ferromagnetic films. , 2001, Physical review letters.

[20]  J. S. Lee,et al.  Spin-transfer torque generated by a topological insulator , 2014, Nature.

[21]  T. T. Sheng,et al.  Microstructure, growth, resistivity, and stresses in thin tungsten films deposited by rf sputtering , 1973 .

[22]  Hyun-Woo Lee,et al.  Magnetization dynamics induced by in-plane currents in ultrathin magnetic nanostructures with Rashba spin-orbit coupling , 2011, 1111.3422.

[23]  Zhang,et al.  Spin hall effect in the presence of spin diffusion , 2000, Physical review letters.

[24]  Aurelien Manchon,et al.  Nonequilibrium intrinsic spin torque in a single nanomagnet , 2008 .

[25]  D. Ralph,et al.  Spin-Torque Switching with the Giant Spin Hall Effect of Tantalum , 2012, Science.

[26]  I. Miron,et al.  Current-induced spin–orbit torques , 2011, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences.

[27]  Comparison of spin-orbit torques and spin pumping across NiFe/Pt and NiFe/Cu/Pt interfaces , 2015, 1503.04104.

[28]  R. Matyi,et al.  Fabrication of 5-20 nm thick β-W films , 2014 .

[29]  A. Brataas,et al.  Spin-orbit torques in action. , 2014, Nature nanotechnology.

[30]  A. S. Cooper,et al.  SUPERCONDUCTIVITY IN FILMS OF BETA TUNGSTEN AND OTHER TRANSITION METALS , 1965 .

[31]  S. Parkin,et al.  Domain-wall velocities of up to 750 m s(-1) driven by exchange-coupling torque in synthetic antiferromagnets. , 2015, Nature nanotechnology.

[32]  D. Ralph,et al.  Magnetic oscillations driven by the spin Hall effect in 3-terminal magnetic tunnel junction devices. , 2012, Physical review letters.

[33]  S. Seo,et al.  Tilting of the spin orientation induced by Rashba effect in ferromagnetic metal layer , 2010 .

[34]  V. M. Edelstein.  Spin polarization of conduction electrons induced by electric current in two-dimensional asymmetric electron systems , 1990 .

[35]  J. Hirsch.  Spin Hall Effect , 1999, cond-mat/9906160.

[36]  G. Dresselhaus.  Spin-Orbit Coupling Effects in Zinc Blende Structures , 1955 .

[37]  David V. Baxter,et al.  Structure and stability of sputter deposited beta‐tungsten thin films , 1994 .

[38]  A. Manchon,et al.  Theory of spin torque due to spin-orbit coupling , 2009 .

[39]  Inverse spin Hall effect : A , 2016 .

[40]  Parkin,et al.  Origin of enhanced magnetoresistance of magnetic multilayers: Spin-dependent scattering from magnetic interface states. , 1993, Physical review letters.

[41]  S. Parkin,et al.  Chiral spin torque at magnetic domain walls. , 2013, Nature nanotechnology.

[42]  Y. Mai,et al.  Residual stress, microstructure, and structure of tungsten thin films deposited by magnetron sputtering , 2000 .

[43]  Hyun-Woo Lee,et al.  Orbital chirality and Rashba interaction in magnetic bands , 2013 .

[44]  E. A. Newman,et al.  Magnetism and Magnetic Materials , 1969 .

[45]  H. Jaffrès,et al.  Spin pumping and inverse spin Hall effect in platinum: the essential role of spin-memory loss at metallic interfaces. , 2013, Physical review letters.

[46]  R. Gross,et al.  Spin Hall magnetoresistance induced by a nonequilibrium proximity effect. , 2012, Physical review letters.

[47]  M. Yao,et al.  Deep inner-shell multiphoton ionization by intense x-ray free-electron laser pulses. , 2012, Physical review letters.

[48]  G. Xiao,et al.  Beta (β) tungsten thin films: Structure, electron transport, and giant spin Hall effect , 2015 .

[49]  G. Beach,et al.  Current-driven dynamics of chiral ferromagnetic domain walls. , 2013, Nature materials.

[50]  Determination of intrinsic spin Hall angle in Pt , 2014, 1410.1601.

[51]  K. Starke,et al.  Rashba effect at magnetic metal surfaces , 2005 .

[52]  D. Apalkov,et al.  Matching domain-wall configuration and spin-orbit torques for efficient domain-wall motion , 2012, 1210.3049.

[53]  A. Hoffmann.  Spin Hall Effects in Metals , 2013, IEEE Transactions on Magnetics.

[54]  Gang Xiao,et al.  Giant Spin Hall Effect and Switching Induced by Spin-Transfer Torque in a W / Co 40 Fe 40 B 20 / MgO Structure with Perpendicular Magnetic Anisotropy , 2015 .