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Observing differential spin currents by resonant inelastic X-ray scattering

Nature volume 645, pages 900–905 (2025)Cite this article

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Abstract

Controlling spin currents, that is, the flow of spin angular momentum, in small magnetic devices, is the principal objective of spin electronics, a main contender for future energy-efficient information technologies1,2. A pure spin current has never been measured directly because the associated electric stray fields and/or shifts in the non-equilibrium spin-dependent distribution functions are too small for conventional experimental detection methods optimized for charge transport3,4. Here we report that resonant inelastic X-ray scattering (RIXS) can bridge this gap by measuring the spin current carried by magnons—the quanta of the spin wave excitations of the magnetic order—in the presence of temperature gradients across a magnetic insulator. This is possible due to the sensitivity of the momentum- and energy-resolved RIXS intensity to minute changes in the magnon distribution under non-equilibrium conditions. We use the Boltzmann equation in the relaxation time approximation to extract transport parameters, such as the magnon lifetime at finite momentum, essential for the realization of magnon spintronics.

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Fig. 1: Structural, spectroscopic and magnetic properties of YIG at 300 K.
Fig. 2: Spin Seebeck device, SSE voltage and RIXS spectra at 300 K.
Fig. 3: Non-equilibrium RIXS measurement at 80 K.
Fig. 4: Magnon distribution function.

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Data availability

Data supporting the findings of this study are available upon reasonable request from the corresponding authors.

Change history

  • 17 September 2025

    In the version of the article initially published, the department names in affiliations 4 and 11 were switched and have now been corrected in the HTML and PDF versions of the article. Affiliation 4 now reads “Institute for Materials Research, Tohoku University, Sendai, Japan” and affiliation 11 now reads “WPI Advanced Institute for Materials Research, Tohoku University, Sendai, Japan”.

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Acknowledgements

This work was primarily supported by the US Department of Energy (DOE), Office of Science, Early Career Research Program. The SSE setup was co-supported as part of Programmable Quantum Materials, an Energy Frontier Research Center funded by the DOE, Office of Science, Basic Energy Sciences (BES), under award no. DE-SC0019443. This research used beamline 2-ID of the National Synchrotron Light Source II and the Nanofabrication and Electron Microscopy facilities of the Center for Functional Nanomaterials (CFN), which are DOE, Office of Science User Facilities operated for the DOE Office of Science by Brookhaven National Laboratory under contract no. DE-SC0012704. G.E.W.B. was supported by JSPS Kakenhi Grant Nos. JP22H04965 and JP24H02231. T.K. and E.S. were supported by the JST CREST (JPMJCR20C1 and JPMJCR20T2), the Grant-in-Aid for Scientific Research (grant nos. JP19H05600 and JP24K01326) and the Grant-in-Aid for Transformative Research Areas (grant no. JP22H05114) from JSPS KAKENHI, MEXT Initiative to Establish Next-Generation Novel Integrated Circuits Centers (X-NICS) (grant no. JPJ011438), Japan, and the Institute for AI and Beyond of the University of Tokyo. T.K. also acknowledges support from the Reimei Research Program of Japan Atomic Energy Agency. J.B. acknowledges support from a Royal Society University Research Fellowship. Finally, we are grateful to P. Gambardella, J. P. Hill and C. Mazzoli for their discussions and to D. Bacescu for the engineering support with the sample environment.

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Author notes

  1. Yanhong Gu

    Present address: State Key Laboratory of Low Dimensional Quantum Physics, Beijing Tsinghua Institute for Frontier Interdisciplinary Innovation, Beijing, China

Authors and Affiliations

  1. National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, NY, USA

    Yanhong Gu, Jiemin Li, John Sinsheimer, Lukas Lienhard, Jonathan Pelliciari & Valentina Bisogni

  2. Bragg Centre for Materials Research, University of Leeds, Leeds, UK

    Joseph Barker

  3. School of Physics and Astronomy, University of Leeds, Leeds, UK

    Joseph Barker

  4. Institute for Materials Research, Tohoku University, Sendai, Japan

    Joseph Barker & Gerrit E. W. Bauer

  5. Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Japan

    Takashi Kikkawa

  6. Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, USA

    Fernando Camino & Kim Kisslinger

  7. Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA

    Jackson J. Bauer & Caroline A. Ross

  8. Department of Physics, Columbia University, New York, NY, USA

    Dmitri N. Basov

  9. Department of Applied Physics, The University of Tokyo, Tokyo, Japan

    Eiji Saitoh

  10. Institute for AI and Beyond, The University of Tokyo, Tokyo, Japan

    Eiji Saitoh

  11. WPI Advanced Institute for Materials Research, Tohoku University, Sendai, Japan

    Eiji Saitoh & Gerrit E. W. Bauer

  12. RIKEN Center for Emergent Matter Science (CEMS), Wako, Japan

    Eiji Saitoh

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Contributions

V.B. conceived the research project. Y.G. and V.B. designed the study, with contributions from G.E.W.B., J.B. and J.P.; J.J.B. checked the magnetization measurement of the YIG single crystal with guidance from C.A.R.; Y.G. fabricated the SSE devices with help from V.B., F.C., K.K., T.K., E.S., D.N.B. and J.S.; Y.G., J.L., J.P. and V.B. carried out the RIXS measurements and performed the first data interpretation. Y.G. analysed the RIXS data with guidance from V.B.; J.B. and G.B. contributed to the data discussion and the linearized Boltzmann model. L.L. performed the finite element analysis of the temperature gradient across the sample; and Y.G. and V.B. wrote the paper with contributions from all authors.

Corresponding authors

Correspondence to Yanhong Gu or Valentina Bisogni.

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Extended data figures and tables

Extended Data Fig. 1 Top view of the RIXS scattering geometry.

a, Experimental set-up for momentum transfer q0.2 = [0.2, 0.2, 0.2] r.l.u. The circularly polarized x-rays ki impinge the sample at an angle θin = 90°. The scattering angle 2Θ between incoming beam ki and outgoing beam kf is fixed at 150°. b, As a but for momentum transfer q−0.2 = [−0.2, −0.2, −0.2] r.l.u., with θin = 60° and 2Θ = 150°.

Extended Data Fig. 2 RIXS measurements as a function of temperature on a reference sample.

a, RIXS spectra measured for q0.2 with T = 80 K (blue scattered line) and T = 107 K (light blue scattered line) from the reference sample. b, The intensity difference ΔI between the spectra shown in the panel a drops into the noise level.

Extended Data Fig. 3 RIXS spectra at different sample locations.

a, Sketch of the device, in which the color bar indicates temperature differences, similar to Fig. 2a in the main text. b, Magnon accumulation/depletion as a function of position x calculated for a constant gradient in a symmetric sample. The accumulation/depletion decays on the scale of the magnon relaxation length λ = 2 μm in red and 10 μm in black. c (e), RIXS spectra for q0.2 measured at the hot point (cold point) for two temperature gradients ΔT2 (dark blue) and ΔT4 (light blue). d (f), The RIXS intensity difference between spectra for ΔT2 and ΔT4 and their Gaussian fit (solid line).

Extended Data Fig. 4 Gaussian fitting of the RIXS spectra in the non-equilibrium state.

The data were all acquired at T = 80 K and versus ΔT (ΔT2, ΔT3, and ΔT4), at q0.2= [0.2, 0.2, 0.2] r.l.u. a, and at q−0.2 = [−0.2, −0.2, −0.2] r.l.u. b. The triangles refer to the experimental data points and the solid lines are the fit by the model in Fig. 1c. The (gold, blue, light-blue)-shaded areas are the extracted (elastic, acoustic magnon, optical magnon) contributions, respectively.

Extended Data Table 1 Reported magnon relaxation times at the Brillouin zone center
Full size table

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Gu, Y., Barker, J., Li, J. et al. Observing differential spin currents by resonant inelastic X-ray scattering. Nature 645, 900–905 (2025). https://doi.org/10.1038/s41586-025-09488-9

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