The dynamical behaviour of thin film magnetic multilayers is a rich and diverse area of research and allows a unique opportunity to design and explore the high frequency properties of magnetic materials. Due to the high quality magnetic tunnel junctions (MTJs) produced at our state-of-the-art facilities at INL, we are able to design systems which not only allow us to explore the fundamental dynamics of such systems, but also to target future and emerging technologies, including 5G wireless communications, bio-inspired neuromorphic computing architectures and wireless energy harvesting. By carefully controlling the geometry and material properties of the magnetic and adjacent non-magnetic layers, novel spin textures, such as magnetic vortices, bubbles and skyrmions, can be created, and their dynamical behaviour explored. The dynamic modes of the these magnetic materials can be excited via spin transfer torque, local magnetic fields or Spin Hall induced spin currents.
Here at INL we focus on three key areas of high frequency dynamics utilising magnetic tunnel junctions:

Spin Torque Nano-Oscillators

In the Spintronics group at INL we specialize in the deposition, characterization and exploitation of Spin torque nano-oscillators (STNOs) for future and emerging technologies. We use a range of magnetic alloys (CoFe, FeB, CoFeB, NiFe) and explore their magnetic dynamical response when excited by electrical currents and magnetic fields. We investigate a range of magnetic textures, from in-plane and out-of-plane uniform magnetised free layers to more novel magnetic textures, i.e. magnetic vortices, bubbles and Skyrmions. By harnessing these dynamic magnetic systems, we target an exciting range of applications and are actively pursuing the demonstrator level prototypes and integration of these STNOs in CMOS technologies in order to prove their industrial viability for future products.
During 2013 to 2016, INL was able to demonstrate the ability to produce STNOs with power values up to 200 nW in homogeneous free-layers, reasonable linewidths and monochromatic spectrums using MTJs using thicker insulating barriers for junctions than typically used. This research focused on this role of the tunnel barrier in the dynamics.

Spin Hall Nano-Oscillators

Spin Hall nano-oscillators are believe to be the potential replacement of spin-torque nano-oscillators with increase reliability, output and high device endurance. The three goals of this projects were the following:

  • Generation of pure spin current in Ta Hall bar.
  • Nanofabrication of 3-terminal device with high quality magnetic tunnel junctions.
  • Detection of high frequency oscillations in 3-terminal spin Hall nano-oscillators

Results: We Experimentally demonstrate a high performance 3-terminal STNOs based on MTJs with a concurrent spin injection from a spin-polarized tunneling current and a pure spin Hall current. A combination of both current efficiently excites the free layer into dynamic regimes which is six times larger than the oscillation amplitudes achieved by either of the individual mechanisms.

Spin wave detection

Integration of MTJs on waveguide structures to allow efficient detection of spin waves for 5G technologies, magnonic logic and coupled arrays.

Tarequzzaman, M; Böhnert, T; Decker, M; Costa, J D; Borme, J; Lacoste, B; Paz, E; Jenkins, A S; Serrano-Guisan, S; Back, C H; Ferreira, R; Freitas, P P

Spin torque nano-oscillator driven by combined spin injection from tunneling and spin Hall current Journal Article

Communications Physics, 2 (1), pp. 20, 2019, ISSN: 2399-3650.

Abstract | Links | BibTeX

Tarequzzaman, M; Jenkins, A S; Böhnert, T; Borme, J; Martins, L; Paz, E; Ferreira, R; Freitas, P P

Broadband voltage rectifier induced by linear bias dependence in CoFeB/MgO magnetic tunnel junctions Journal Article

Applied Physics Letters, 112 (25), pp. 252401, 2018, (arXiv: 1804.04104).

Abstract | Links | BibTeX

Tarequzzaman, M; Bohnert, T; Jenkins, A S; Borme, J; Paz, E; Ferreira, R; Freitas, P P

Influence of MgO Tunnel Barrier Thickness on the Output Power of Three-Terminal Spin Hall Nano-Oscillators Journal Article

IEEE Transactions on Magnetics, pp. 1–4, 2018.

Links | BibTeX

Costa, J D; Serrano-Guisan, S; Lacoste, B; Jenkins, A S; Böhnert, T; Tarequzzaman, M; Borme, J; Deepak, F L; Paz, E; Ventura, J; Ferreira, R; Freitas, P P

High power and low critical current density spin transfer torque nano-oscillators using MgO barriers with intermediate thickness Journal Article

Scientific Reports, 7 (1), 2017.

Links | BibTeX

Costa, J D; Serrano-Guisan, S; Borme, J; Deepak, F L; Tarequzzaman, M; Paz, E; Ventura, J; Ferreira, R; Freitas, P P

Impact of MgO Thickness on the Performance of Spin-Transfer Torque Nano-Oscillators Journal Article

IEEE Transactions on Magnetics , 51 (11), 2015.

Links | BibTeX

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