Johan Åkerman

Ultra-fast spectrum analysis based on rapidly tuned spintronic nano-oscillators has been under development for the last few years and has already demonstrated promising results. Here, we demonstrate an ultra-fast microwave spectrum analyzer based on a chain of five mutually synchronized nano-constriction spin Hall nano-oscillators (SHNOs). As mutual synchronization affords the chain a much improved signal quality, with linewidths well below 1 MHz at close to a 10 GHz operating frequency, we observe an order of magnitude better frequency resolution bandwidth compared to previously reported spectral analysis based on single magnetic tunnel junction based spin torque nano-oscillators. The high-frequency operation and ability to synchronize long SHNO chains and large arrays make SHNOs ideal candidates for ultra-fast microwave spectral analysis.

Optical coherent Ising machines based on time-multiplexing have demonstrated significant progress in terms of connectivity and spin scalability. However, they are constrained by large physical footprints, high power consumption, poor thermal stability, and high cost. Here, we present a time-multiplexed Ising machine leveraging propagating wave packets in solid-state delay lines at radio frequencies, enabling thermally stable, robust, low-power, tabletop, and affordable design. We use two serially connected 20.5 MHz, 707 μ s bulk acoustic wave delay lines supporting 2048 spins. Our design provides all-to-all connectivity with 15-bit coupling resolution and finds approximate MAX-CUT solutions in 341 ms, potentially scalable to sub-ms by using higher frequency delay lines. Additionally, we demonstrate solutions to number partitioning and Sudoku problems. Compared with state-of-the-art Coherent Ising machines, our machine exhibits four orders of magnitude higher thermal stability. Against the simulated bifurcation algorithm, our design achieves comparable results on the MAX-CUT problem, while outperforming it on the more complex number-partitioning and Sudoku problems.

Van der Waals (vdW) magnets with room-temperature ferromagnetism offer exciting opportunities for energy-efficient spintronic devices, yet their magnetization dynamics remain largely unexplored despite their importance for high-speed memory technologies. Here, we investigate spin–orbit torque phenomena in the room-temperature vdW magnet (Co0.15Fe0.85)5GeTe2 (CFGT)/Pt heterostructure using spin-torque ferromagnetic resonance and second-harmonic Hall measurements. Alongside a conventional in-plane spin Hall conductivity of 3.68 × 105 (ℏ/2e) (Ω m)−1, we identify a sizable out-of-plane component of −0.33 × 105 (ℏ/2e) (Ω m)−1 that generates unconventional damping-like torques. Density functional theory and Monte Carlo simulations suggest that this torque can originate from interface-induced spin reorientation arising from a modified magnetic anisotropy landscape and strongly enhanced Dzyaloshinskii–Moriya interaction at the CFGT/Pt interface. The combination of low effective magnetization (0.321 T), moderate Gilbert damping (0.027), and efficient multidirectional torques highlights vdW magnets as promising platforms for next-generation spintronic devices.

Spin-orbit-torque-driven auto-oscillations in spin Hall nano-oscillators (SHNOs) provide a promising route toward energy-efficient, nanoscale microwave devices for neuromorphic computing and high-frequency technologies. Achieving robust oscillations requires lowering the threshold current (I_th), governed by the spin Hall efficiency (θ_SH). Conventional approaches to enhance θ_SH often involve trade-offs, such as increased resistivity and interfacial effects. Here, we demonstrate a pronounced enhancement of the bulk spin Hall effect in PtBi alloys via crystallographic engineering, achieving a 3-fold increase in θ_SH from 0.07 in Pt_100.0Bi_0.0 to 0.24 in Pt_94.0Bi_6.0 and 0.19 in Pt_91.3Bi_8.7, extracted from DC-bias spin-torque ferromagnetic resonance. The enhancement arises from bulk-dominated extrinsic side-jump scattering. Correspondingly, I_th is reduced by 42% and 32% in 100 nm SHNOs based on Co₄₀Fe₄₀B₂₀(3 nm)/Pt_94.0Bi_6.0(4 nm) and Co₄₀Fe₄₀B₂₀(3 nm)/Pt_91.3Bi_8.7(4 nm), respectively. The devices exhibit narrower linewidths (∼25 MHz), enhanced quality factors (350 ≤ Q ≤ 550, ∼4× higher than Pt (Pt_100.0Bi_0.0)), and a 61.6% reduction in threshold power. These findings establish PtBi alloys as efficient spin Hall materials, enabling reduced power consumption for SHNO-based neuromorphic and memory technologies.

Networks of coupled oscillators underpin fundamental studies of collective dynamics and emerging paradigms in physical computing. Spin Hall nano-oscillators (SHNOs) are particularly attractive due to their scalability and fast spin-wave-mediated interactions, yet mutual synchronization has so far been limited to small arrays and predominantly steady-state characterization. Here we demonstrate nanosecond phase ordering in lattices of up to N = 105,000 constriction-type SHNOs with widths of 10–20 nm. Microwave spectra reveal full mutual synchronization, a quality factor exceeding 10 ⁶ , power scaling as N and linewidth scaling as N ⁻¹ . Time-resolved Brillouin light scattering shows a weak, approximately logarithmic increase in the synchronization time with array size. The synchronization time varies from 10 ns in arrays of 100 SHNOs to 45 ns for the largest arrays and is consistent with Kuramoto-type collective phase-ordering dynamics in a large two-dimensional oscillator lattice. These results establish spin-wave-mediated SHNO lattices as an experimentally accessible platform for exploring collective oscillator physics and for developing embedded-Ising and reservoir-computing architectures operating at tens of gigahertz.

Independent control of coercivity (H_C) and exchange bias (H_EB) in ferromagnetic/antiferromagnetic (FM/AFM) heterostructures is essential for optimizing perpendicular spintronic devices, including magnetic random-access memory (MRAM) and nanoscale magnetic sensors, yet remains challenging due to their shared interfacial origin. In this work, we demonstrate a systematic approach to decouple these properties in [Co/Pd] multilayers (MLs) exchange-coupled to FeMn by engineering the stacking sequence and antiferromagnetic layer thickness (t_FeMn). Two configurations—top-pinned [Co/Pd]/FeMn and bottom-pinned FeMn/[Co/Pd]—were fabricated using magnetron sputtering. Despite exhibiting similar fcc(111) texture, the two structures display markedly different magnetic responses. The bottom-pinned configuration promotes rotatable uncompensated spins, resulting in a significant enhancement of HC (up to 1440 Oe) with negligible HEB. In contrast, the top-pinned configuration stabilizes pinned uncompensated spins, leading to a pronounced perpendicular exchange bias (up to 188 Oe) with minimal impact on H_C. By varying t_FeMn, H_C and H_EB can be tuned independently over wide ranges. These results demonstrate that stacking-sequence-dependent interfacial spin configurations govern magnetic behavior rather than bulk structural differences, providing a practical and scalable strategy for designing high-stability reference layers and low-switching-energy free layers in advanced spintronic devices.

The droplet-like PSW exhibits a hybrid character, combining a localized core with propagating spin-wave behavior, which distinguishes it from both conventional droplet solitons and standard PSWs.

Spin-based computing is emerging as a powerful approach for energy-efficient and high-performance solutions to future data processing hardware. Spintronic devices function by electrically manipulating the collective dynamics of the electron spin, which is inherently non-volatile, nonlinear and fast operating, and can couple to other degrees of freedom such as photonic and phononic systems. This Technical Review explores key advances in integrating magnetic and spintronic elements into computational architectures, ranging from fundamental components such as radiofrequency neurons or synapses and spintronic probabilistic bits to broader frameworks such as reservoir computing and magnetic Ising machines. For each of these systems, we discuss hardware-specific and task-dependent metrics to evaluate their computing performance and evaluate the physical processes that need to be optimized to increase performance. Finally, we discuss challenges and future opportunities, highlighting the potential of spin-based computing in next-generation technologies.

Constriction-based spin Hall nano-oscillators (SHNOs) show great promise for application as highly tunable microwave sources with straightforward scalability toward large coupled networks. However, details of the magnetization dynamics within SHNOs have thus far not been addressed experimentally, due to the minute time and length scales involved. In this work, we present direct imaging of the magnetization dynamics within a single CoFeB-based SHNO using time-resolved scanning transmission X-ray microscopy (STXM). Our measurements reveal that the magnon amplitude is the strongest at the two constriction edges, with a pronounced assymetry favoring one edge, and that emitted spin waves exhibit strongly anisotropic propagation. Micromagnetic simulations suggest that grain boundaries and the Dzyaloshinskii-Moriya interaction (DMI) play a key role in both effects. Furthermore, the magnetodynamics changed during the measurement, indicating that the CoFeB/MgO interface may be more susceptible to X-ray induced modifications than previously recognized, challenging its presumed radiation hardness.