Farzad Mahfouzi: Difference between revisions

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==Title==
==Title==
Spin-orbit torque and spin pumping in topological-insulator/ferromagnet heterostructures
Spin-orbit torques and spin pumping in lateral and vertical topological-insulator/ferromagnet heterostructures


==Talk abstract==  
==Abstract==  
Topological insulators (TIs) are newly discovered class of Dirac materials which possess an energy gap in the bulk, akin to conventional band insulators, while hosting metallic surfaces where electrons behave as massless Dirac fermions analogous to the ones found in graphene. However, unlike graphene where spin-orbit coupling (SOC) is negligible due to the lightness of carbon atoms, in TIs it plays a crucial role by locking the direction of spin and momentum of surface electrons. This feature is considered to be a great resource for spintronic applications where combinations of TIs with ferromagnets (FM) could lead to ultralow-power memory and logic devices. On the other hand, graphene is envisaged as interconnect in lateral devices due to long spin diffusion lengths or perfect spin filtering barrier in vertical heterostructures where it is sandwiched by Co or Ni layers. In this talk, I will discuss possible routes of integration of grapheme and TIs with FMs into vertical and lateral heterostructures exhibiting:  (i) perfect spin filtering at finite bias voltage and spin-transfer torque driven by low injected current in Ni/few-layer-graphene/Ni and Co/few-layer-graphene/Co vertical heterostructures; (ii) current-driven SO torques by which TI surface induces magnetization dynamics of the FM layer; and (iii) spin-to-charge conversion after the magnetization of the FM overlayer on the surface of TI is brought into steady state precession by the microwave absorption.  
Topological insulators (TIs) are newly discovered class of Dirac materials which possess an energy gap in the bulk, akin to conventional band insulators, while hosting metallic surfaces where electrons behave as massless Dirac fermions analogous to the ones found in graphene. However, unlike graphene, where the spin-orbit coupling (SOC) is negligible due to the lightness of carbon atoms, in TIs it plays a crucial role by locking the direction of spin and momentum of surface electrons. This feature is considered to be a great resource for spintronic applications where combinations of TIs with ferromagnets (FM) could lead to ultralow-power memory and logic devices. In this talk, I will discuss our theoretical proposals for integration of TIs with FMs into both ''vertical'' and ''lateral'' heterostructures exhibiting:  (i) current-driven SO torques by which TI surface induces magnetization dynamics of the FM layer; and (ii) spin pumping and spin-to-charge conversion after the magnetization of the FM overlayer on the surface of TI is brought into steady state precession by the microwave absorption.


==References==
==References==
[1] F. Mahfouzi, B. K. Nikolić, and N. Kioussis, '''Large antidamping-like spin-orbit torque driven by spin-flip reflection mechanism on the surface of a topological insulator,''' arXiv:1506.01303.
* F. Mahfouzi, B. K. Nikolić, and N. Kioussis, ''Large antidamping-like spin-orbit torque driven by spin-flip reflection mechanism on the surface of a topological insulator,'' [http://arxiv.org/abs/1506.01303 arXiv:1506.01303].
[3] F. Mahfouzi, N. Nagaosa, and B. K. Nikolić, “Spin-to-charge conversion in lateral and vertical topological-insulator/ferromagnet heterostructures with microwave-driven precessing magnetization,” Phys. Rev. B 90, 115432 (2014).
* F. Mahfouzi, N. Nagaosa, and B. K. Nikolić, ''Spin-to-charge conversion in lateral and vertical topological-insulator/ferromagnet heterostructures with microwave-driven precessing magnetization,'' [http://dx.doi.org/10.1103/PhysRevB.90.115432 Phys. Rev. B '''90''', 115432 (2014)].
[4] K. K. Saha, A. Blom, K. S. Thygesen, and B. K. Nikolić, “Magnetoresistance and negative differential resistance in Ni/Graphene/Ni vertical heterostructures driven by finite bias voltage: A first-principles study,” Phys. Rev. B 85, 184426 (2012).
* F. Mahfouzi, N. Nagaosa, and B. K. Nikolić, ''Spin-orbit coupling induced spin-transfer torque and current polarization in topological-insulator/ferromagnet vertical heterostructures,'' [http://dx.doi.org/10.1103/PhysRevLett.109.166602 Phys. Rev. Lett. '''109''', 166602 (2012)].
[5] F. Mahfouzi, N. Nagaosa, and B. K. Nikolić, “Spin-orbit coupling induced spin-transfer torque and current polarization in topological-insulator/ferromagnet vertical heterostructures,Phys. Rev. Lett. 109, 166602 (2012).
* F. Mahfouzi, B. K. Nikolić, S.-H. Chen, and C.-R. Chang, ''Microwave-driven ferromagnet–topological-insulator heterostructures: The prospect for giant spin battery effect and quantized charge pump devices,'' [http://dx.doi.org/10.1103/PhysRevB.82.195440 Phys. Rev. B '''82''', 195440 (2010)].
[6] F. Mahfouzi, B. K. Nikolić, S.-H. Chen, and C.-R. Chang, “Microwave-driven ferromagnet–topological-insulator heterostructures: The prospect for giant spin battery effect and quantized charge pump devices,Phys. Rev. B 82, 195440 (2010).

Latest revision as of 23:02, 10 August 2015

Affiliations

  • Department of Physics, California State University, Northridge, CA 91330-8268, USA

Title

Spin-orbit torques and spin pumping in lateral and vertical topological-insulator/ferromagnet heterostructures

Abstract

Topological insulators (TIs) are newly discovered class of Dirac materials which possess an energy gap in the bulk, akin to conventional band insulators, while hosting metallic surfaces where electrons behave as massless Dirac fermions analogous to the ones found in graphene. However, unlike graphene, where the spin-orbit coupling (SOC) is negligible due to the lightness of carbon atoms, in TIs it plays a crucial role by locking the direction of spin and momentum of surface electrons. This feature is considered to be a great resource for spintronic applications where combinations of TIs with ferromagnets (FM) could lead to ultralow-power memory and logic devices. In this talk, I will discuss our theoretical proposals for integration of TIs with FMs into both vertical and lateral heterostructures exhibiting: (i) current-driven SO torques by which TI surface induces magnetization dynamics of the FM layer; and (ii) spin pumping and spin-to-charge conversion after the magnetization of the FM overlayer on the surface of TI is brought into steady state precession by the microwave absorption.

References

  • F. Mahfouzi, B. K. Nikolić, and N. Kioussis, Large antidamping-like spin-orbit torque driven by spin-flip reflection mechanism on the surface of a topological insulator, arXiv:1506.01303.
  • F. Mahfouzi, N. Nagaosa, and B. K. Nikolić, Spin-to-charge conversion in lateral and vertical topological-insulator/ferromagnet heterostructures with microwave-driven precessing magnetization, Phys. Rev. B 90, 115432 (2014).
  • F. Mahfouzi, N. Nagaosa, and B. K. Nikolić, Spin-orbit coupling induced spin-transfer torque and current polarization in topological-insulator/ferromagnet vertical heterostructures, Phys. Rev. Lett. 109, 166602 (2012).
  • F. Mahfouzi, B. K. Nikolić, S.-H. Chen, and C.-R. Chang, Microwave-driven ferromagnet–topological-insulator heterostructures: The prospect for giant spin battery effect and quantized charge pump devices, Phys. Rev. B 82, 195440 (2010).