Northwestern Events Calendar

May
13
2016

Robert Buhrman: Understanding and Utilizing Magnetic Torques Arising from Spin-Orbit Interactions in Heavy Metal/Ferromagnetic Multilayers

When: Friday, May 13, 2016
3:30 PM - 4:30 PM CT

Where: Technological Institute, L211, 2145 Sheridan Road, Evanston, IL 60208 map it

Audience: Faculty/Staff - Student - Public

Contact: Pamela Villalovoz   13645

Group: Physics and Astronomy Colloquia

Category: Academic

Description:

Title: Understanding and Utilizing Magnetic Torques Arising from Spin-Orbit Interactions in Heavy Metal/Ferromagnetic Multilayers

Speaker: Robert Buhrman, Cornell University


Abstract: In the spin Hall effect (SHE) the passage of a longitudinal charge current density through a non-ferromagnetic metal (NM) film generates, through either an intrinsic (band structure) or extrinsic (defect scattering) spin-orbit interaction, a transverse pure spin current density that is polarized in-plane and normal to the direction of current flow. When this spin current impinges onto an adjacent ferromagnetic (FM) film the spin current that is transverse to the local moment of the FM will either be reflected with some spin rotation, or absorbed. In the former case this results in a “field-like torque” being exerted on the FM through the transfer of spin angular momentum. In the latter case, the spin transfer results in a non-conservative “damping-like” torque where, depending on the orientation of the spin polarization relative to the magnetic moment of the FM, this torque either removes magnetic excitation energy from the FM, increasing its damping, or adds excitation energy to it. While initially thought to be a weak effect, certain NMs (e.g. Pt, Ta, and W) have all been found to exhibit a strong SHE, with the internal spin Hall ratio, , of Pt now being determined as being as high as 0.2, and even higher, > 0.3, in the beta (A-15) phase of W. It has as well been shown recently that current induced torques can also arise from spin-orbit interactions at the FM/NM interface and/or at a FM/insulator interface due to the lack of inversion symmetry there (Rashba-Edelstein effect). These recently identified, and sometimes robust spin-orbit torques are currently of strong interest due to the richness of the underlying electronic transport phenomena, and because they open up new possibilities for the efficient manipulation of magnetization at the nanoscale for technology applications, including high performance memory. In this talk I will discuss some recent studies that have sought to establish the dominant origin of spin-orbit torques in a number of HM/FM/Insulator systems, and discuss methods that can enhance their strength through control and modification of the HM/FM interface. I will also briefly review the status of what currently appears to be one of the more promising technological applications of spin-orbit torques.

Host: Bill Halperin

Keywords: Physics, Astronomy, colloquium

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