A new milestone in magnonics has been achieved with the first measurement and quantitative analysis of thermal spin-wave spectra in individual cylindrical magnetic nanowires. Spin waves—collective oscillations of magnetization in ferromagnets—are promising for low-power logic and data transfer, but their physics has largely been explored in bulk crystals or thin films. Theory predicts that 3D nanostructures will host novel effects such as quantization and non-reciprocity due to curvature and finite size, yet experimental confirmation in single conduits was missing.

Researchers at Spintec, in collaboration with Universidad Complutense (Madrid) and C2N & LPS (Paris-Saclay), have now filled this gap. They synthesized 100-nm-diameter wires of Fe₂₀Ni₈₀, a prototypical soft-magnetic material, via electroplating in anodized alumina templates that were subsequently chemically dissolved. Individual wires were placed on a silicon surface and probed using micro-Brillouin Light Scattering (µBLS), which resolves sub-micron areas and spin waves with wave vectors up to about 40 rad/μm. Thermal spin waves—existing at room temperature without external excitation—were recorded as a function of applied longitudinal magnetic field, revealing up to seven distinct peaks at each field value.

All peaks were globally fitted with just two magnetic parameters (magnetization and exchange stiffness) using the open-source finite-element code TetraX. Each mode was assigned a pair of indices: a radial index l and an azimuthal index m, corresponding to the nodal structure of the dynamic magnetization components. This indexing, analogous to standing spin waves in thin films, permitted a precise determination of the material’s exchange stiffness.

These results open the door to exploring exotic physics and functionalities in 3D magnetic conduits, including non-reciprocal spin-wave behavior in curved magnetization textures with azimuthal components, and interactions with domain walls, chemical modulations, or wire branching. The work, published in Physical Review B (vol. 113, 134423, 2026), sets the stage for advanced spin-wave generation, manipulation, and detection in three-dimensional nanosystems.

Spin waves are propagating fundamental excitations of magnetic systems, also carrying promises for low-power logic and data transfer. We report the measurement of thermal spin-wave spectra in single cylindrical nanowires, and their quantitative analysis as modes with a radial and azimuthal index. This opens the route for more elaborate investigations including generation, manipulation and detection.

Measured and fitted spectra (left) and simulated modes (top) of spin waves in a nanowire. The color codes the direction and magnitude of magnetization oscillation with radial (1st row) and azimuthal (2nd row) directions.

Spin waves (or magnons, their particle-like counterpart), are a collective oscillation of magnetization vectors in a ferromagnet, either thermal or resulting from an excitation. Until now, their physics and potential for device functionality have been probed mostly in either bulk crystals or thin films and circuits. In parallel, theory has outlined new physics to be expected in 3D nanosystems, related to finite-size and curvature, such as quantization and non-reciprocity. In order to confirm this new physics and unlock its potential for 3D devices, a first milestone is their measurement and modelling in individual conduits.

We have considered cylindrical wires of about 100 nm in diameter made of Fe20Ni80, the prototypical soft-magnetic material, displaying homogeneous and longitudinal magnetization. These were synthesized with electroplating in anodized alumina porous templates, the latter ultimately dissolved chemically. Individual wires were laid on a Si surface and measured with micro-Brillouin Light Scattering (µBLS), a technique that probes an area below a micrometer squared and spin waves with wave vector k up to roughly 40 rad/μm. Spectra of thermal spin waves (i.e., existing at room temperature without the need for excitation by a device) were measured versus applied longitudinal field for better discrimination. Up to seven peaks were measured for each value of applied field, which we could fit globally with a single set of two magnetic parameters (magnetization and exchange stiffness) using the open finite-element modeling code TetraX (see figure). Every mode is associated with a set of radial l and azimuthal m indexes, which relate to the number of nodes of the radial mr and mφ components of the dynamic magnetization. Similar to standing spin waves in thin films, this allows a precise determination of exchange stiffness of the material.

This first measurement and quantitative understanding of spin waves in individual cylindrical nanowires paves the way for the exploration of both exciting physics and related applicable functionalities. This includes the non-reciprocity of spin waves for peculiar 3D magnetization distributions, such as with an azimuthal component, and their coupling with domain walls, chemical modulations or branching.

Team: Spin Textures

Collaborations: Universidad Complutense (Madrid), C2N & LPS (Paris-Saclay)

Further reading: Experimental determination and micromagnetic analysis of spin wave modes in cylindrical nanowires, N. Martin, L. Alvaro-Gomes, L. Perez, A. Thiaville, J.P. Adam, O. Fruchart & A. Masseboeuf, Phys. Rev. B, 113 (13), 134423 (2026). Open access: hal-05231476

Open access: cea-05003501v1 and cea-05003507v1

Contact: Olivier Fruchart and Aurelien Masseboeuf

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