Neutron Spectroscopy Used to Separate Magnetic Modes

12 February 2025

The magnetic properties of iron oxide nanoparticles play a fundamental role in numerous applications ranging from hyperthermia in cancer treatment to adaptive shock absorbers for the car industry. Still, many details of their magnetic signatures remain unclear. Prof. Zobel’s (JCNS-3) team has now arrived at a comprehensive view, separating three magnetic modes by accessing the magnetic dynamics using high-resolution neutron spectroscopy experiments at the high flux reactor at the ILL, Grenoble.

The breakthrough comes from an analysis of data in a wide angular range since scattering information at different angles corresponds to different length scales, so that discrete magnetic phenomena become visible.

The researchers identified superparamagnetic relaxations relevant e. g. for internal body heating by external excitation. They found direct evidence of this property, a superspin fluctuation between easy crystallographic directions, in the small angle regime where large-size phenomena prevail. In addition, a coherent magnetic excitation of 23 µeV, also named "magnon", was identified at the first Bragg peak representing atomic Fe-Fe correlations.

The third magnetic signature is a weak relaxation present at all length scales representing isolated spins in a thin magnetic shell of the nanoparticles whose structural identity was previously shown to exist using magnetic small angle neutron scattering.

Original publication:

Separating spin dynamics modes in iron oxide nanoparticles
M. Zobel, M. Appel, S. L. J. Thomä, M. Plekhanov, and A. Magerl
Phys. Rev. B 111, L060406 – Published 11 February, 2025
DOI: https://doi.org/10.1103/PhysRevB.111.L060406