Zero-temperature spin-glass freezing in self-organized arrays of Co nanoparticles

TL;DR

This study investigates the magnetic glassy dynamics in self-organized Co nanoparticle arrays across different dimensionalities, revealing zero-temperature spin-glass behavior with similar phenomena in 2D and 3D limits.

Contribution

It demonstrates that the glassy magnetic dynamics in nanoparticle arrays is consistent across 2D and 3D, supporting a zero-temperature spin-glass transition model.

Findings

No qualitative difference between 2D and 3D magnetic responses.

Critical slowing down follows an activated scaling law.

Magnetic correlations extend mainly to nearest neighbors.

Abstract

We study, by means of magnetic susceptibility and magnetic aging experiments, the nature of the glassy magnetic dynamics in arrays of Co nanoparticles, self-organized in N layers from N=1 (two-dimensional limit) up to N=20 (three-dimensional limit). We find no qualitative differences between the magnetic responses measured in these two limits, in spite of the fact that no spin-glass phase is expected above T=0 in two dimensions. More specifically, all the phenomena (critical slowing down, flattening of the field-cooled magnetization below the blocking temperature and the magnetic memory induced by aging) that are usually associated with this phase look qualitatively the same for two-dimensional and three-dimensional arrays. The activated scaling law that is typical of systems undergoing a phase transition at zero temperature accounts well for the critical slowing down of the dc and ac susceptibilities of all samples. Our data show also that dynamical magnetic correlations achieved by aging a nanoparticle array below its superparamagnetic blocking temperature extend mainly to nearest neighbors. Our experiments suggest that the glassy magnetic dynamics of these nanoparticle arrays is associated with a zero-temperature spin-glass transition.