Moore's Law, which has governed the exponential increase in transistor density in integrated circuits since the 1960s, is facing significant challenges. The escalating power consumption and resultant heat generation severely limit further miniaturization and performance improvements. To overcome this obstacle, research is shifting towards non-charge-based information carriers. Magnons, collective excitations of magnetic moments, offer a promising alternative. Unlike charge currents, magnons can transmit spin information without electron movement, eliminating Joule heating. This inherent energy efficiency makes magnons ideal candidates for post-Moore era electronics. The field effect transistor (FET) is a cornerstone of modern electronics, and creating a magnonic equivalent is highly desirable. However, controlling magnon currents with electric fields is challenging due to the weak coupling between electric fields and magnetic moments. While research has explored electric field-induced spin wave frequency shifts, controlling magnon flow with an electric field has remained elusive. Previous attempts at creating magnon transistors have employed various approaches, including vertical magnon current transmission and gating with electric currents or magnetic fields. However, the development of a three-terminal, electric field-controlled, lateral magnon FET that is highly energy efficient and nonvolatile remains a substantial challenge. This paper presents a novel design and experimental demonstration of such a device.

Numerous studies have explored magnonic devices, focusing on various aspects of magnon transport and manipulation. Research on magnon spintronics highlights the potential of magnons as information carriers, emphasizing their ability to carry spin information without electron flow, thus reducing energy consumption. Studies have explored the transmission of electrical signals by spin-wave interconversion, control of spin chemical potential, and non-local magnetoresistance in YIG/Pt nanostructures. Other work has demonstrated magnon-mediated current drag and the mutual control of coherent spin waves and magnetic domain walls. Theoretical and experimental investigations have explored electric-field-induced frequency shifts in spin waves, however, the electric field control of magnon flow remains a significant challenge in the field. Prior work on magnon transistors has utilized different configurations, including vertical structures and gating methods involving electric currents or magnetic fields. However, the development of a lateral three-terminal device exhibiting nonvolatile electric field control at room temperature remained elusive until this study.

The researchers designed a three-terminal lateral magnon FET consisting of three parallel heavy metal (HM) nano-stripes (Pt) on a ferromagnetic or ferrimagnetic insulator (FI) film (Y3Fe5O12) deposited on a ferroelectric (FE) material (Pb(Mg1/3Nb2/3)0.7Ti0.3O3 or Pb(Zr0.52Ti0.48)O3). The stripes act as source (S), gate (G), and detector (D). A 60-nm-thick YIG film was deposited onto PMN-PT or PZT substrates. Three parallel Pt stripes (550 nm wide, 15 µm long, 3.5 nm thick) were patterned on top of the YIG film using electron beam lithography. In-plane and out-of-plane I-V curves confirmed the insulating behavior of the YIG film even with applied gate voltage. Non-local measurements of magnon transport were performed using both AC and DC currents. In AC measurements, a low-frequency AC current was applied to the source stripe, and the first and second harmonic non-local voltages at the detector stripe were measured as a function of the angle between the applied magnetic field and the stripe direction. In DC measurements, a DC current was applied to the source stripe, and the non-local voltage at the detector stripe was measured as a function of the applied magnetic field and the distance between the source and detector stripes. To demonstrate the magnon FET, a voltage pulse was applied to the gate stripe, and the modulation of the magnon propagation was measured via the voltage change at the detector stripe. Before measurements, multiple cycles of gate voltage sweeping were performed to minimize the memory effect. Magnetic field-dependent non-local voltage measurements were performed under different gate voltage pulses to characterize the nonvolatile behavior of the device. To further probe the device characteristics, additional measurements were done on different devices with varying gate stripe widths and using different substrates, and supplemental temperature, strain, and local spin Seebeck effect measurements were conducted to elucidate the underlying mechanism for the observed electric-field-induced magnon current modulation. Piezoelectric force microscopy (PFM) confirmed nonvolatile ferroelectric domain switching in the PMN-PT substrate.

The study successfully demonstrated a nonvolatile three-terminal lateral magnon FET operating at room temperature. Non-local measurements confirmed the lateral magnon transport in the Y3Fe5O12 film. The angular dependence of the first and second harmonic non-local voltages was consistent with the expected contributions from electronically injected and thermally excited magnon currents. The DC non-local voltage showed an exponential decay with the distance between the source and detector stripes, yielding a magnon diffusion length of 1.42 ± 0.20 μm. Applying gate voltage pulses resulted in a significant modulation of the non-local voltage, demonstrating electric field control of the magnon current. Importantly, this modulation was nonvolatile, persisting even after removal of the gate voltage pulse. A high on/off ratio of up to ~400% was achieved. Further investigations ruled out temperature gradient and strain changes as the primary mechanism for the observed modulation, pointing instead towards a change in magnon relaxation within the YIG channel potentially caused by polarization-dependent ion accumulation or interactions with collective excitations in the PMN-PT. A device fabricated with a thinner PZT film showed a smaller but still significant on/off ratio under lower gate voltages, indicating potential for miniaturization and reduction of operational voltage. A comparison with previous reports on three-terminal lateral magnon transistors highlights the unique advantages of this device, particularly its combination of high on/off ratio, electric field control, nonvolatility, and room-temperature operation.

The successful demonstration of a nonvolatile, room-temperature, three-terminal magnon FET represents a significant advance in magnon spintronics. The high on/off ratio achieved is crucial for practical applications in logic circuits. The nonvolatile nature of the device significantly improves energy efficiency compared to volatile devices. The ability to control magnon transport using an electric field offers advantages in terms of integration with existing semiconductor technologies. The findings open up new possibilities for developing energy-efficient magnon-based logic devices and suggest potential applications in unconventional computing, such as neuromorphic computing. The proposed mechanisms for the observed electric-field-induced modulation warrants further investigation through techniques like Brillouin light scattering or inelastic neutron scattering to fully clarify the interaction between the ferroelectric polarization and magnon transport.

This study successfully demonstrated a nonvolatile, three-terminal lateral magnon FET exhibiting a high on/off ratio at room temperature. The device's nonvolatile nature and electric field control provide significant advantages in terms of energy efficiency and scalability. This achievement opens new avenues for developing low-power, energy-efficient magnon-based logic devices and paves the way for exploring novel computing architectures. Future research should focus on further miniaturizing the device, reducing the operational voltage, and exploring different ferroelectric materials for improved performance and integration with existing semiconductor technologies.

The use of a relatively thick (0.5 mm) PMN-PT substrate necessitated the use of high gate voltages (200 V). While a device with a thinner PZT film demonstrated operation at lower voltages, further optimization is needed to achieve truly low-voltage operation. The exact mechanism for the electric field induced modulation of magnon transport remains to be fully elucidated. The relatively small number of devices tested might limit the generalization of some observations. Further studies with a larger sample set are needed to fully explore the variability in device performance.