Abstract. Low energy (16 keV) muons were used to probe the dynamic magnetic behaviour of iron nanoclusters embedded in a silver thin film matrix. The silver film was 500 nm thick and contained a volume fraction of 0.1% iron. Measurements were made in a field of 25 mT, applied normal to the plane of the film, in the temperature range 4.7 K to 300 K. At temperatures above 20 K thermal activation of the cluster moments was seen as a narrowing of the field distribution sensed by the implanted muons. An intrinsic cluster relaxation time of τ₀ = 12 ± 4 ns and an activation energy of 51 ± 9 K were deduced from fits to the data. SQUID magnetometry of thicker (1.5 µm) but otherwise identical films on graphite substrates showed the clusters to have a volume of the order of 10^-26 m³, from which a cubic anisotropy constant of K = 2.3 ± 0.4 × 10⁵ J m^-3 was calculated. Remanence measurements showed no evidence of a preferred orientation for the magnetization of the cluster assembly.

Print publication: Issue 7 (21 February 2000)
Received 25 November 1999