Classical percolation models predict the metal-insulator transition and the onset of the long-range ferromagnetic order at the same topological continuity threshold. We tested this prediction in thin films of ferromagnetic CoPd and found a dramatic difference between the conductance and magnetic thresholds. While the long-range ferromagnetic phase develops at or very close to the continuity threshold, the transition from the metal-like to insulator-like conductance develops in films several times thinner. We argue that atomically narrow low resistance gaps intersecting the fractal network of metallic clusters provide a consistent explanation of the effect. We identify the conduction threshold as the point in discontinuous films at which the resistance of intergranular junctions exceeds the quantum resistance mark.
@article{arxiv.2503.01377,
title = {Conductance, continuity, and ferromagnetic percolation thresholds in thin films},
author = {Gregory Kopnov and Alexander Gerber},
journal= {arXiv preprint arXiv:2503.01377},
year = {2025}
}