A nonvolatile magnon field effect transistor at room temperature

The study addresses the challenge of heat dissipation in advanced electronics by exploring magnon-based information transport, which avoids Joule heating associated with charge motion. While the field effect transistor is foundational to electronics, creating a magnonic analogue that can be efficiently controlled by electric fields is difficult due to weak coupling between electric fields and magnetic moments. Prior work has demonstrated electric-field-induced spin-wave frequency shifts but not direct electric-field control over magnon flow. The research question is whether a lateral, three-terminal, room-temperature magnon transistor can be realized with nonvolatile, electric-field gating to modulate magnon transport with high on/off ratios. The work is significant for enabling low-power magnonic logic and potential neuromorphic applications.

Previous magnon transistor implementations have used vertical transport or gating via electric current or magnetic fields rather than pure electric-field control, and lacked a three-terminal lateral geometry suitable for cascading. Reported three-terminal lateral devices include microwave-controlled YIG systems with very large modulation but without nonvolatility, current-controlled devices with modest room-temperature modulation, and magnetic-field-controlled devices at room temperature but without nonvolatility. A van der Waals device exhibited electrical switching at cryogenic temperatures. The present work, summarized against prior art (Table 1), uniquely combines room-temperature operation, electric-field control, nonvolatility, and a large on/off ratio (~400%), addressing limitations in earlier studies.

Device structure: A ~60 nm Y3Fe5O12 (YIG) film was sputtered on (011)-oriented PMN-PT single crystal or on (001)-oriented PZT films. Three parallel Pt stripes (~550 nm wide, 15 µm long, 3.5 nm thick) were patterned on YIG to act as source (S), gate (G), and detector (D). A bottom electrode aligned with G was fabricated beneath the ferroelectric. Structural and magnetic properties are in Supplementary Note 1. YIG remained insulating under gating (Supplementary Note 2). All measurements were at room temperature. Non-local magnon transport measurement: Two-terminal non-local configuration (S and D). An AC current (I0 = 0.71 mA at 15.7 Hz) was injected into S; first (V1) and second (V2) harmonic non-local voltages at D were recorded versus in-plane field angle α. Fits yielded V1 ∝ cos α and V2 ∝ cos 2α, attributing V1 to electrically injected magnons via SHE and V2 to thermally generated magnons via SSE. To avoid capacitive/inductive artefacts, DC non-local measurements were conducted: VDC versus field angle and current showed cos α dominance and VDC ∝ IDC^2, confirming thermal origin. Distance dependence: devices with varying S–D center-to-center distance d showed exponential decay of VDC, yielding magnon diffusion length λ = 1.42 ± 0.20 µm. Magnon FET operation: Three-terminal devices were prepared. Gate voltage pulses VG were applied at G; non-local VDC at D was measured after removing the gate field (remnant state), demonstrating nonvolatile control. Prior to measurements, VG was swept between −200 V and +200 V several cycles to reduce memory effects. VDC versus in-plane magnetic field (α = 0) was recorded for various VG. VDC amplitude (half-difference between saturation states) displayed a hysteretic dependence on VG resembling the ferroelectric charge loop, indicating correlation with FE polarization switching. On/off ratio was evaluated from VDC amplitudes at remnant states after ±VG pulses. Control experiments for mechanism: Local temperature changes at S and D were inferred from resistance under DC heating; ΔT between S and D was nearly constant versus VG, excluding temperature gradient changes as the dominant mechanism. PMN-PT(011) strain versus voltage showed a symmetric butterfly with tiny remanence, insufficient to explain large nonvolatile modulation. Local SSE at S, D, and G after VG = ±200 V showed S and D signals nearly unchanged; G exhibited a small change attributable to G-stripe resistance/heating power. Spin Hall magnetoresistance (SMR) of Pt/YIG at G was independent of VG, indicating unchanged interfacial spin reflection. PFM confirmed nonvolatile FE domain switching. Methods details: film growth (YIG on PMN-PT, post-anneal 800 °C, 4 h; PZT 400 nm on Nb:STO at 550 °C, Ar/O2 15/1, 10 mTorr), device fabrication (e-beam lithography, sputtering, lift-off), and electrical measurement setups (lock-in for harmonics, voltmeter for DC, source-meters for VG).

• Demonstration of a nonvolatile three-terminal lateral magnon FET operating at room temperature, with electric-field gating via a ferroelectric substrate (PMN-PT or PZT).
• Non-local magnon transport characterization:
  • Angular dependence: V1 ∝ cos α (electrically injected magnons), V2 ∝ cos 2α (thermally generated magnons via SSE).
  • DC regime: VDC dominated by cos α, with VDC ∝ IDC^2 (thermal origin), confirming SSE dominance at low frequency.
  • Distance dependence: VDC decays exponentially with center-to-center distance d; extracted magnon diffusion length λ = 1.42 ± 0.20 µm in sputtered polycrystalline YIG.
• Electric-field control of magnon transport:
  • VDC amplitude exhibits a nearly square hysteresis versus VG, closely tracking the FE charge loop, demonstrating correlation with FE polarization states and nonvolatile control.
  • Device 1: on/off ratio ~400% between remnant states after ±200 V pulses; VDC amplitude ~130 nV at +200 V remanence, nearly vanishing near −110 V.
  • Device 2: on/off ratio ~115% for ±200 V pulses; differences attributed to substrate composition variations and fabrication-induced discrepancies.
  • PZT-based device (400 nm PZT on Nb:STO): on/off ratio ~28% (magnitude) under ±10 V gating.
• Control experiments indicate the modulation is not due to changes in temperature gradient (ΔT between S and D nearly constant), not dominated by FE strain (butterfly strain with tiny remanence), and not due to variations in generation/detection efficiency or interfacial spin transparency (local SSE at S and D unchanged; SMR independent of VG).

The observed electric-field-induced, nonvolatile modulation of lateral magnon transport is attributed primarily to altered magnon relaxation within the YIG channel, mediated by coupling to the ferroelectric polarization. Changes in magnetic anisotropy from magnetoelectric coupling cannot account for the large modulation, as anisotropy mainly affects small-wavevector magnons and has limited impact on broadband thermally excited magnons central to SSE-driven transport. A plausible mechanism is polarization-dependent ion (Fe3+ or O2−) accumulation in interfacial YIG layers, modifying exchange stiffness and magnon relaxation. Additional contributions may arise from coupling between YIG magnons and collective FE excitations (ferrons/phonons) or interactions between magnon-induced electric dipoles and FE polarization. The combined effects could produce the large observed modulation. From a device perspective, the present implementation uses a 0.5-mm-thick FE substrate requiring ±200 V; thinning FE layers can reduce gate voltage to the volt range. Integration prospects include PMN-PT films on Si and PZT films, which already demonstrate significant modulation at ±10 V. Lateral scaling to sub-micrometer distances is feasible, given the exponential decay of magnon currents and the localized nature of FE domain switching. Compared to previous three-terminal magnon transistors, this work uniquely combines room-temperature operation, electric-field gating, nonvolatility, and large on/off ratio, making it a strong candidate for low-power magnonic logic and neuromorphic applications. Further spectroscopy (e.g., Brillouin light scattering or inelastic neutron scattering) could clarify microscopic mechanisms and quantify gate-dependent magnon parameters.

The study realizes a long-sought three-terminal magnon field effect transistor: a lateral YIG/Pt device gated by a ferroelectric (PMN-PT or PZT) that operates nonvolatilely at room temperature with a high on/off ratio (~400%). The device demonstrates robust electric-field control of thermally generated magnon transport and suggests mechanisms tied to FE polarization–dependent modifications of magnon relaxation. This advance paves the way for energy-efficient magnon-based logic and unconventional computing (e.g., neuromorphic). Future work should lower operating voltage via thin-film FE integration, scale down device dimensions, and employ spectroscopic probes to unravel and optimize the gating mechanism.

• High gate voltage (±200 V) required due to thick (0.5 mm) PMN-PT substrates; thin-film FE layers are needed to reduce operating voltage to the volt range.
• Device-to-device performance variability (on/off ratio ranging from ~20% to ~400%) likely due to substrate composition variations, FE domain nonuniformity, and fabrication differences.
• Mechanism not fully resolved; difficult at present to extract gate-dependent magnon diffusion length; further spectroscopic studies are needed.
• Current demonstration relies primarily on thermally generated magnons (SSE) at low frequencies; electrically injected contributions are less dominant in DC regime.
• Lateral device size is micrometer-scale; systematic scaling studies toward nanoscale operation remain for future work.