PGI Kolloquium: Prof. Dr. Johan Åkerman, University of Gothenburg, Gothenburg, Sweden

Online Talk

Please note: You will receive the link to the online talk in the e-mail invitation, usually sent out a few days before the lecture takes place. It is also available on request from the contact person below.

Voltage Controlled Mutual Synchronization of Spin Hall Nano-oscillator Arrays – a Route towards Spintronic Ising Machines

Mutually synchronized spin torque nano-oscillators (STNOs) are one of the promising platforms for bioinspired computing and microwave signal generation [1, 2]. Using STNOs one can achieve 90% recognition rate in spoken vowels [3]. However, for more complex tasks, larger scale synchronized oscillators are needed, something that is not easily done with the STNOs demonstrated so far.

I will describe a different spin current driven device called a spin Hall nano-oscillator (SHNO) [4], based on 50 – 120 nm wide nano-constrictions in Pt(5)/Hf(0.5)/NiFe(3) trilayers (numbers in nm).  When multiple SHNOs are fabricated close to each other (300 – 1200 nm separation) they can mutually synchronize; chains of up to 21 SHNOs have been demonstrated to exhibit complete synchronization [5]. We can also synchronize two-dimensional SHNO arrays with 8 x 8 = 64 SHNOs [6]. The mutual synchronization is observed both electrically and using scanning micro-BLS microscopy. Both the output power and linewidth of the microwave signal improves substantially with increasing number of mutually synchronized SHNOs, such that quality factors of about 170,000 can be reached. Following the approach of Romera et al [3], we also demonstrate neuromorphic computing using 4 x 4 SHNO arrays with two injected microwave signals as inputs.

I will then show how we can use voltage gates to control individual oscillators in arrays of W/CoFeB/MgO based SHNOs [7]. Thanks to their perpendicular magnetic anisotropy (PMA) these SHNOs can produced propagating spin waves [8] and through the voltage control of their PMA, the effective damping of the SHNO can be tuned by up to 42% [9].

Finally, I will briefly describe our efforts in constructing an Oscillator Ising Machine [10] based on STNOs [11] and SHNOs [12]. Given their high operating frequency (~10 GHz), easy fabrication, and highly robust voltage-controlled synchronization properties, nano-constriction SHNO arrays are likely the most promising candidates for neuromorphic computing and Ising Machines based on oscillator networks.

[1]      

J. Grollier, D. Querlioz, and M. D. Stiles, Proc. IEEE 104, 2024 (2016)

.

[2]      J. Torrejon et al, Nature 547, 428 (2017)

[3]      M. Romera et al, Nature 563, 230–234 (2018)

[4]      T. Chen, R. K. Dumas, A. Eklund, P. K. Muduli, A. Houshang, A. A. Awad, P. Dürrenfeld, B. G. Malm, A. Rusu, and J. Åkerman, Proc.

IEEE 104, 1919 (2016)

[5]      A. A. Awad, P. Dürrenfeld, A. Houshang, M. Dvornik, E. Iacocca, R. K. Dumas, and J. Åkerman, Nature Physics 13, 292–299 (2017)

[6]      M. Zahedinejad, A. A. Awad, S. Muralidhar, R. Khymyn, H. Fulara, H. Mazraati, M. Dvornik, and J. Åkerman, Nature Nanotechnology

, 47 (2020)

[7]       M. Zahedinejad, H. Fulara, R. Khymyn, A. Houshang, S. Fukami, S. Kanai, H. Ohno, and J. Åkerman, Nature Materials, under review; arXiv:2009.06594 (2020)

[8]       H. Fulara, M. Zahedinejad, R. Khymyn, A. A. Awad, S. Muralidhar, M. Dvornik, and J. Åkerman, Science Advances

, eaax8467 (2019)

[9]       H. Fulara, M. Zahedinejad, R. Khymyn, M. Dvornik, S. Fukami, S. Kanai, H. Ohno, and J. Åkerman, Nature Communications

, 4006 (2020)

[10]    T. Wang, L. We, P. Nobel, and J. Roychowdhury, Natural Computing (2021)

[11]    D. I. Albertsson, M. Zahedinejad, A. Houshang, R. Khymyn, J. Åkerman, and A. Rusu, Appl. Phys. Lett.

, 112404 (2021)

[12]    A. Houshang, M. Zahedinejad, S. Muralidhar, J. Checinski, A. A. Awad, and J. Åkerman, arXiv:2006.02236 (2020)

Kontakt

Gustav Bihlmayer

Telefon: +49 2461 61-4677

Fax:  +49 2461 61-2850

E-Mail: g.bihlmayer@fz-juelich.de