Itinerant Ferromagnetism in the Electronic Localization Limit

We present Hall effect, R-xy(H), and magnetoresistance, R-xx(H), measurements of ultrathin films of Ni, Co, and Fe with thicknesses varying between 0.2 and 8 nm and resistances between 1 M Omega and 100 Omega. Both measurements show that films having a resistance above a critical value R-C, (thickness below a critical value, d(C)) show no signs of ferromagnetism. Ferromagnetism appears only for films with R < R-C, where R-C is material dependent. We raise the possibility that the reason for the absence of spontaneous magnetism is the suppression of itinerant ferromagnetism by electronic disorder in the strong localization regime.