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Just as electronic shot noise in driven conductors results from the granularity of charge and the statistical variation in the arrival times of charge carriers, there are predictions for fundamental noise in magnon currents due to angular momentum being carried by discrete excitations. The inverse spin Hall effect as a transduction mechanism to convert spin current into charge current raises the prospect of experimental investigations of such magnon shot noise. Spin Seebeck effect measurements have demonstrated the electrical detection of thermally driven magnon currents and have been suggested as an avenue for accessing spin current fluctuations. Using spin Seebeck structures made from yttrium iron garnet on gadolinium gallium garnet, we demonstrate the technical challenges inherent in such noise measurements. While there is a small increase in voltage noise in the inverse spin Hall detector at low temperatures associated with adding a magnetic field, the dependence on field orientation implies that this is not due to magnon shot noise. We describe theoretical predictions for the expected magnitude of magnon shot noise, highlighting ambiguities that exist. Further, we show that magnon shot noise detection through the standard inverse spin Hall approach is likely impossible due to geometric factors. Implications for future attempts to measure magnon shot noise are discussed.
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This content will become publicly available on March 1, 2027
Observation of the Magnon Hall Magnetoresistance Effect
Interconversion between charge and spin currents via spin-orbit coupling underpins spin orbitronics. Magnons, which are the quanta of spin waves, can exchange angular momentum with conduction-electron spins through spin-flip scattering, suggesting a direct route for charge-to-magnon conversion. Here, we predict that in single-layer ferromagnets, an applied electric current induces a transverse magnon current, producing electrical magnon Hall and inverse magnon Hall effects that share the symmetry of the spin Hall and inverse spin Hall effects. This effect gives rise to a magnon Hall magnetoresistance in CoFeB and NiFe, with an efficiency comparable to the spin Hall effect and a characteristic decay length on the order of micrometers, far exceeding typical electron spin diffusion lengths. By enabling the direct generation and detection of long-range magnon currents, our findings open new pathways for low-loss, on-chip spin-based logic and energy-harvesting devices.
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- PAR ID:
- 10673385
- Publisher / Repository:
- Physical Review Letters
- Date Published:
- Journal Name:
- Physical Review Letters
- Volume:
- 136
- Issue:
- 11
- ISSN:
- 0031-9007
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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