Nanoconstriction spin Hall Nano-oscillators (SHNOs)

In spin Hall nano-oscillators (SHNOs), the dissipationless pure spin current, generated by the spin Hall effect phenomenon, excites the nanoscopic magnetic regions into auto-oscillations at GHz frequencies. SHNOs are strongly tunable and rapidly modulated microwave nano-oscillators directly compatible with CMOS technology. While their first target applications are ultra-wide frequency tunable microwave signal generators/detectors for cell phones, wireless networks, and vehicle radar, the highly nonlinear properties governing mutual synchronization make SHNOs the most promising candidates for oscillator-based neuromorphic computing schemes.

List of related Papers:     

1. Controllable Frequency Tunability in Constriction-based Spin Hall Nano-oscillators for Neuromorphic Computing
   Arunima TM and Himanshu Fulara*,  Journal of Physics D: Applied Physics 58, 125001 (2025).

2. CMOS compatible W/CoFeB/MgO spin Hall nano-oscillators with wide frequency tunability
   M. Zahedinejad, H. Mazraati, Himanshu Fulara, J. Yue, S. Jiang, A. A. Awad, and  J. Åkerman, Applied Physics Letters, 112, 132404 (2018).  

Spin Hall nano-oscillator based neuromorphic computing

Our brain performs highly sophisticated cognitive tasks, such as image and speech recognition, with an exceptionally lower energy budget and much greater efficiency than that of today's computer. Therefore, it is natural to look for artificial neurons which can mimic brain-inspired processes to match the human brain's efficiency. The development of such energy-efficient and tunable devices has been a long research goal for decades. We have recently demonstrated how two-dimensional arrays of SHNOs are capable of performing vowel recognition at GHz frequencies.

List of related Papers:     

1. Two-dimensional mutually synchronized spin Hall nano-oscillator arrays for neuromorphic computing
   M. Zahedinejad, A. A. Awad, S. Muralidhar, R. Khymyn, Himanshu Fulara, H. Mazraati, M. Dvornik, and J. Åkerman, Nature Nanotechnology  47 – 52 (2020)

2. Robust mutual synchronization in long spin Hall nano-oscillator chains
   Akash Kumar, Himanshu Fulara, Roman Khymyn, Artem Litvinenko, Mohammad Zahedinejad, Mona Rajabali, Xiaotian Zhao, Nilamani Behera, Afshin Houshang, Ahmad A Awad, Johan Åkerman, Nano Letters 23, 6720–6726 (2023).

Energy-efficient voltage control of SHNOs

To program such SHNO arrays for complex cognitive neuromorphic tasks, individual oscillator control is essentially required. We recently developed a voltage-controlled spin Hall nano-oscillator, where both the microwave frequency and the threshold current can be strongly tuned in an energy-efficient manner using a voltage-induced electric field. Using memristive gates in such constriction-based SHNO chains, we also demonstrated non-volatile voltage control of the mutually synchronized states of SHNO networks. This in a way ensures non-volatile independent tuning of the synaptic interactions between two artificial oscillator neurons driven by pure spin currents.

List of related Papers:            

1. Memristive control of mutual SHNO synchronization for neuromorphic computing
   M. Zahedinejad, Himanshu Fulara, R. Khymyn, A. Houshang, M. Dvornik, S. Fukami, S. Kanai, H. Ohno, and J. Åkerman, Nature Materials  21, 81 – 87 (2022).

2. Giant voltage control of spin Hall nano-oscillator damping
   Himanshu Fulara, M. Zahedinejad, R. Khymyn, M. Dvornik, S. Fukami, S. Kanai, H. Ohno, and J. Åkerman, Nature Communications 11, 4006 (2020).               

Beyond CMOS spin-wave computing – Magnonics

Imagine tossing a pebble into a lake and watching exquisite water waves rippling out around the spot in an ever-expanding ring. In our earlier work, we have shown such an identical ripple of energy – the so-called propagating spin waves, can be straightforwardly excited and strongly tuned under certain conditions in spin Hall nano-oscillator devices. This was achieved by allowing the substantial ease to the magnetic easy axis from lying within the film plane to along the film normal under minimal operational current. The capability to locally excite propagating spin waves at the nanoscale has tremendous potential to operate next-generation devices at higher microwave frequencies with faster data transfer and without any energy loss. In addition, their current tunability effectively makes these oscillators tunable nanoscale sources of ultra-short spin-wave pulses.

List of related Papers:   

1. Spin-orbit torque–driven propagating spin waves
   Himanshu Fulara, M. Zahedinejad, R. Khymyn, A. A. Awad, S. Muralidhar, M. Dvornik, and J. Åkerman, Science Advances 5, eaax8467 (2019). 

Micromagnetic modelling and simulations of spin Hall nanodevices

We perform micromagnetic modelling and simulations to gain deep insights into the magnetization dynamics of various spin Hall nanodevices. Recently, we demonstrated the controlled nucleation of topologically distinct skyrmion-antiskyrmion metastable states, skyrmioniums, and stable skyrmion pairs by leveraging inter spin-texture interactions using two nanocontacts.   These simulations serve as a crucial link between experimental findings and theoretical frameworks, enabling us to bridge existing knowledge gaps. Our goal is to facilitate experimental studies by identifying key physical mechanisms, optimizing device geometries, and predicting emergent phenomena, thereby paving the way for more targeted experimental studies. 

List of related Papers:   

1. Tunable Skyrmion-Antiskyrmion Dynamics in Co/Pt Nanocontacts for Spintronic Applications

Hind Prakash and Himanshu Fulara*, Applied Physics Letters 126, 072403 (2025). 

2. Controllable Frequency Tunability in Constriction-based Spin Hall Nano-oscillators for Neuromorphic Computing
   Arunima TM and Himanshu Fulara*,  Journal of Physics D: Applied Physics 58, 125001 (2025).

Higher-order Slonczewski  propagating spin waves

In his seminal paper [J. Magn. Magn. Mater. 159, L1–L7 (1996)], John Slonczewski predicted higher-order STT-driven propagating spin waves (SWs), however, never realized in experiments due to the much higher current density required to excite such modes. In our earlier work, we demonstrated the so-called sombrero nanocontacts (NCs) in MTJ stacks, the resulting effective nano-contact size was increased, while the tunneling barrier reduced the required current density. Both a 2nd and a 3rd higher-order propagating SW mode were observed, and their wavelengths were estimated to 120 and 74 nm, i.e., much smaller than the 150-nm nanocontact. Mutual synchronization was also observed in all three propagating modes. These higher-order propagating SWs will enable magnonic devices to operate at much higher frequencies, generate much shorter SW wavelengths, and greatly increase their transmission rates and propagation lengths, both proportional to the much higher group velocity.

List of related Papers:   

1. Spin transfer torque driven higher-order propagating spin waves in nanocontact magnetic tunnel junctions
   A. Houshang, R. Khymyn, Himanshu Fulara, A. Gangwar, M. Haidar, S. R. Etesami, R. Ferreira, P. P. Freitas, M. Dvornik, R. K. Dumas, J. Åkerman, Nature Communications 9, 4374 (2018).