Figure 1. ⁵⁹Co FNR spectra of cobalt nanoparticles versus temperature.

(a) The ⁵⁹Co zero field FNR spectra recorded at 2 (black), 4.2 (magenta) and 77 K (blue). (b) TDFNR spectra: in black spectrum measured at 2 K minus spectrum measured at 4.2 K; in magenta spectrum at 4.2 K minus spectrum at 77 K; in blue spectrum at 77 K. Co can have an f.c.c. or an h.c.p. structure and be in two magnetic states: single domain or multi-domain. (c) The fractions of cobalt atoms engaged in the different blocking temperature ranges. (d) Numbers of Co particles per mg of cobalt (N_p mg_Co⁻¹) in different blocking temperature ranges. 2–4.2 K range corresponds to 3–4 nm particles, 4.2–77 K range to 4–10 nm; >77 K corresponds to particles larger than 10 nm.