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arxiv: 2604.25431 · v1 · submitted 2026-04-28 · ❄️ cond-mat.mtrl-sci

From Ultrafast Demagnetization to Ultrafast Spintronics : a 30 years story

Quentin Remy (1 , 2) , St\'ephane Mangin (1 , 3) ((1) Universit\'e de Lorraine , CNRS , Institut Jean Lamour , Nancy , France
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(2) Department of Physics Freie Universit\"at Berlin Berlin Germany (3) Center for Science Innovation in Spintronics Tohoku University Sendai Japan)
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Pith reviewed 2026-05-07 15:58 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci
keywords ultrafast demagnetizationfemtomagnetismall-optical switchingultrafast spintronicsspin currentsmagnetization reversalangular momentum transferfemtosecond lasers
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The pith

Ultrafast demagnetization enables femtosecond spin injection for field-free magnetization reversal in spintronic devices.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper traces the development of the field from the 1996 discovery of laser-induced ultrafast demagnetization to the current capabilities of ultrafast spintronics. It shows how this rapid quenching of magnetic order creates spin currents and spin polarization that can be harnessed for switching. A central advance is the demonstration of single-pulse all-optical switching in certain ferrimagnets and the extension to deterministic reversal in spin valves and tunnel junctions using femtosecond pulses. Readers should care because the resulting switching occurs at femtojoule energies and three orders of magnitude faster than conventional methods, pointing toward high-speed, low-power magnetic technologies for information processing.

Core claim

The 1996 observation of femtosecond laser-induced ultrafast demagnetization revealed that angular momentum can leave the spin system on sub-picosecond timescales, generating spin-flips, magnons, and spin currents. These processes enabled helicity-independent single-pulse all-optical switching in rare-earth transition-metal ferrimagnets at femtojoule energies without external fields, and later allowed ultrafast spin injection to drive deterministic magnetization reversal in both ferromagnetic and ferrimagnetic layers inside spin valves and tunnel junctions, operating analogously to spin transfer torque but three orders of magnitude faster.

What carries the argument

Ultrafast spin injection generated by demagnetization, functioning as a femtosecond-scale version of spin transfer torque to reverse magnetization in device structures.

If this is right

  • Deterministic magnetization reversal becomes possible in spin valves and tunnel junctions using only femtosecond optical pulses without external magnetic fields.
  • Both ferromagnetic and ferrimagnetic layers can be switched by ultrafast spin injection at energies on the femtojoule scale.
  • Rare-earth transition-metal alloys function as reference systems for studying angular-momentum flow on femtosecond timescales.
  • High-speed information processing becomes feasible with magnetic devices that consume far less energy than current spin-transfer-torque approaches.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same femtosecond spin-current generation might be adapted to control magnetization in hybrid devices that combine optical and electronic inputs for faster memory access.
  • Extending the approach to additional material classes could reduce reliance on rare-earth elements while preserving the speed advantage.
  • The non-equilibrium angular-momentum dynamics observed here may inform models used in other fields studying rapid energy transfer, such as ultrafast superconductivity or magnonic computing.

Load-bearing premise

The mechanisms linking electrons, phonons, and spins during ultrafast demagnetization are understood well enough that the described switching breakthroughs can be treated as reliable foundations for new devices.

What would settle it

Demonstration that femtosecond optical pulses fail to produce deterministic reversal in rare-earth-free ferromagnetic spin valves or tunnel junctions at room temperature would undermine the claim that ultrafast spin injection provides a general, scalable switching method.

Figures

Figures reproduced from arXiv: 2604.25431 by 2), (2) Department of Physics, 3) ((1) Universit\'e de Lorraine, (3) Center for Science, Berlin, CNRS, France, Freie Universit\"at Berlin, Germany, Innovation in Spintronics, Institut Jean Lamour, Japan), Nancy, Quentin Remy (1, Sendai, St\'ephane Mangin (1, Tohoku University.

Figure 1
Figure 1. Figure 1: Longitudinal MOKE signal of a Ni(22 nm)/MgF₂(100 nm) film as a function of pump-probe delay20. The pump excitation is a 7 mJ/cm2 pulse with a duration of 60 fs duration. The signal is normalized to the static signal without pump. The sharp drop within a few hundred femtoseconds provides the first direct evidence of ultrafast demagnetization, while the picosecond recovery reflects electron-spin-lattice equi… view at source ↗
Figure 2
Figure 2. Figure 2: Schematic representation of the three-temperature model20. Electrons, spins, and phonons are described as coupled subsystems, each characterized by an effective temperature, 𝑇!, 𝑇", and 𝑇#, respectively. Energy is exchanged between these reservoirs through phenomenological coupling/time constants, while each subsystem is assumed to remain internally thermalized at all times. A femtosecond laser pulse only … view at source ↗
Figure 3
Figure 3. Figure 3: Superdiffusive spin transport following femtosecond laser excitation81. Majority and minority hot electrons propagate with different velocities and inelastic mean free paths, producing a transient spin-polarized current that removes angular momentum from the excited region view at source ↗
Figure 4
Figure 4. Figure 4: Terahertz emission from a ferromagnet/normal-metal bilayer92. (a) Femtosecond demagnetization drives an ultrafast spin current into the adjacent heavy metal, where spin￾orbit coupling converts it into an in-plane charge pulse that radiates a broadband THz transient. (b) The excitation transforms slow majority-spin d electrons (red) into fast sp electrons, thereby launching a spin current towards the gold o… view at source ↗
Figure 5
Figure 5. Figure 5: Element-specific XMCD traces in GdFeCo89. The 3d and 4f sublattices demagnetize on distinct timescales, revealing ultrafast inter-sublattice angular-momentum transfer and the formation of a transient ferromagnetic-like state.(a) and (b) correspond to the same dynamics on different timescales. Taken together, these results demonstrate that ultrafast demagnetization does not originate from a single microscop… view at source ↗
Figure 6
Figure 6. Figure 6: (a) Experimentally determined demagnetization rate −𝜕+𝑀 for permalloy (dotted line) using THz emission spectroscopy63. The yellow curve is the time integral of the effective pump-pulse intensity envelope (light grey shaded area). The blue curve is the best fit from the Stoner model (or equivalently a temperature model) while the red curve shows the result of the phenomenological electron-magnon model. The … view at source ↗
Figure 11
Figure 11. Figure 11: Magneto-optical images and all-optical helicity-independent switching (AO-HIS) state diagram for a 20 nm Gd24(FeCo)76 film275. (a) MOKE images of the magnetic configuration after exposure to a single linearly polarized laser pulse with pulse durations of 50 fs, 1 ps, and 3 ps, for increasing fluence (9.5–15 mJ/cm²). Above the switching threshold fluence FSW, deterministic AO-HIS is observed and the switch… view at source ↗
Figure 14
Figure 14. Figure 14: (adapted from Ref.279, cover image). Graphical illustration of interface-enabled single-pulse AO-HIS in a Pt/Co/Pt-based heterostructure by introducing an ultrathin “Gd dusting” layer at one Pt/Co interface, highlighting that deterministic ultrafast switching can be achieved with a very small rare-earth content through interface engineering. It is important to emphasize that AO-HIS in RE-TM ferrimagnets i… view at source ↗
Figure 15
Figure 15. Figure 15: Depth-resolved AO-HIS dynamics in a 9.4 nm Gd25Co75 layer, adapted from view at source ↗
read the original abstract

The discovery of femtosecond laser-induced ultrafast demagnetization in 1996 opened a new field, femtomagnetism, in which magnetic order can be quenched on timescales shorter than a picosecond. This seminal observation revealed that angular momentum can be transferred out of the spin system with unprecedented speed, launching intense efforts to disentangle the roles of electrons, phonons, and spins in the non-equilibrium regime. Soon it became evident that ultrafast demagnetization generates spin-flips, spin polarization, magnons and spin currents, providing new channels for angular-momentum flow. These insights laid the foundation for linking femtomagnetism with spintronics. An emblematic breakthrough in this evolution is the helicity-independent single-pulse all-optical switching (AOS) observed in rare-earth transition-metal (RE-TM) ferrimagnets such as GdFeCo. This mechanism, operating at femtojoule-scale energies and without external magnetic fields, establishes RE-TM alloys as benchmark systems for understanding and exploiting angular-momentum flow at the femtosecond timescale. Building on these concepts, the combination of ultrafast optical excitation with spintronic devices has demonstrated deterministic magnetization reversal driven by femtosecond pulses in spin valves and tunnel junctions, including rare-earth-free systems. Ultrafast spin injection, acting analogously to spin transfer torque but operating three orders of magnitude faster, allows reversal of both ferromagnetic and ferrimagnetic layers. By enabling ultrafast and energy-efficient switching, ultrafast spintronics promises scalable technologies for high-speed information processing while raising fundamental questions about angular momentum transfer in strongly out-of-equilibrium quantum materials.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

0 major / 2 minor

Summary. This manuscript is a historical review tracing the 30-year evolution of femtomagnetism from the 1996 discovery of ultrafast laser-induced demagnetization to its integration with spintronics. It describes how demagnetization generates spin-flips, magnons, and spin currents; highlights the breakthrough of helicity-independent all-optical switching in RE-TM ferrimagnets such as GdFeCo; and covers demonstrations of ultrafast spin injection enabling deterministic magnetization reversal in spin valves and tunnel junctions, including rare-earth-free systems. The narrative concludes by noting the promise of energy-efficient ultrafast switching technologies alongside open questions on angular momentum transfer in out-of-equilibrium materials.

Significance. If the account accurately represents the cited literature, the review provides a coherent synthesis of established experimental milestones, linking fundamental studies of non-equilibrium magnetism to practical spintronic device concepts. It appropriately flags unresolved mechanistic issues rather than claiming full resolution of angular-momentum pathways, which strengthens its utility as a contextual overview for researchers entering or working in the field.

minor comments (2)
  1. [Title] The title contains a grammatical issue: 'a 30 years story' should be revised to 'a 30-year story' (or '30 Years of Story').
  2. [Abstract] The abstract would be strengthened by including direct citations to the seminal 1996 demagnetization work and the key AOS papers on RE-TM alloys, allowing readers to immediately connect the narrative to primary sources.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for the positive evaluation of our historical review and for recommending minor revision. The referee's summary accurately reflects the manuscript's scope, tracing the evolution from ultrafast demagnetization to ultrafast spintronics while highlighting open questions on angular momentum transfer.

Circularity Check

0 steps flagged

No significant circularity; historical review without derivations or self-referential claims

full rationale

This is a review article presenting a chronological narrative of experimental discoveries in femtomagnetism and ultrafast spintronics over 30 years. It summarizes external breakthroughs (e.g., 1996 ultrafast demagnetization, AOS in RE-TM alloys, spin injection in devices) and links them descriptively to applications and open questions on angular momentum transfer. No new quantitative predictions, equations, fits, or derivations are introduced. All load-bearing statements reference established literature rather than reducing to the paper's own inputs or self-citations by construction. The content is self-contained as a factual historical account.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

As a historical review, the paper introduces no new free parameters, axioms, or invented entities. It relies entirely on the established experimental literature in femtomagnetism and spintronics.

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Reference graph

Works this paper leans on

8 extracted references · 2 canonical work pages

  1. [1]

    Carpene, E. et al. Dynamics of electron-magnon interaction and ultrafast demagnetization in thin iron films. Phys. Rev. B - Condens. Matter Mater. Phys. 78, 174422 (2008). 67. Schmidt, A. B. et al. Ultrafast magnon generation in an Fe film on Cu(100). Phys. Rev. Lett. 105, (2010). 68. Manchon, A., Li, Q., Xu, L. & Zhang, S. Theory of laser-induced demagne...

    work page doi:10.1103/physrevresearch.6.013270 2008

  2. [2]

    Mathias, S. et al. Ultrafast element-specific magnetization dynamics of complex magnetic materials on a table-top. J. Electron Spectros. Relat. Phenomena 189, 164–170 (2013). 89. Radu, I. et al. Transient ferromagnetic-like state mediating ultrafast reversal of antiferromagnetically coupled spins. Nature 472, 205–208 (2011). 90. Dornes, C. et al. The ultr...

    2013

  3. [3]

    Xu, Y. et al. Ultrafast Magnetization Manipulation Using Single Femtosecond Light and Hot-Electron Pulses. Adv. Mater. 29, 1703474 (2017). 136. Ishibashi, K. et al. Single-Shot Magnetization Reversal in Ferromagnetic Spin Valves via Heat Control. Phys. Rev. Lett. 135, 116702 (2025). 137. Singh, H. et al. Ultrafast Spin Accumulations Drive Magnetization Re...

    2017

  4. [4]

    Bierhance, G. et al. Spin-voltage-driven efficient terahertz spin currents from the magnetic Weyl semimetals Co2MnGa and Co2MnAl. Appl. Phys. Lett. 120, 82401 (2022). 159. Zhang, Q., Nurmikko, A. V., Miao, G. X., Xiao, G. & Gupta, A. Ultrafast spin-dynamics in half-metallic CrO2 thin films. Phys. Rev. B 74, 064414 (2006). 160. Maehrlein, S. F. et al. Diss...

    2022

  5. [5]

    Möller, C. et al. Verification of ultrafast spin transfer effects in iron-nickel alloys. Commun. Phys. 7, 74 (2024). 181. Jana, S. et al. Atom-specific magnon-driven ultrafast spin dynamics in Fe1-xNix alloys. Phys. Rev. B 107, L180301 (2023). 182. Jana, S. et al. Evidence of an exchange-based origin of demagnetization from the fluence dependent delay of ...

    2024

  6. [6]

    Chekhov, A. L. et al. Ultrafast Demagnetization of Iron Induced by Optical versus Terahertz Pulses. Phys. Rev. X 11, 041055 (2021). 203. Lee, H., Weber, C., Fähnle, M. & Shalaby, M. Ultrafast Electron Dynamics in Magnetic Thin Films. Appl. Sci. 11, 9753 (2021). 204. Légaré, K. et al. Near- and mid-infrared excitation of ultrafast demagnetization in a coba...

    work page doi:10.1038/s41567-025-03143-w 2021

  7. [7]

    El Hadri, M. S. et al. Two types of all-optical magnetization switching mechanisms using femtosecond laser pulses. Phys. Rev. B 94, 064412 (2016). 272. Vahaplar, K. et al. All-optical magnetization reversal by circularly polarized laser pulses: Experiment and multiscale modeling. Phys. Rev. B 85, 104402 (2012). 273. Khorsand, A. R. et al. Role of Magnetic...

    2016

  8. [8]

    Mishra, K. et al. Dynamics of all-optical single-shot switching of magnetization in Tb/Co multilayers. Phys. Rev. Res. 5, 023163 (2023). 296. Melnikov, A. et al. Ultrafast spin transport and control of spin current pulse shape in metallic multilayers. Phys. Rev. B 106, 104417 (2022). 297. Kimel, A. V. & Li, M. Writing magnetic memory with ultrashort light...

    2023