S. Yamamuro et al., Structural and magnetic evolution in self-assembling process of nanometer-sized Co clusters, MATER T JIM, 40(12), 1999, pp. 1450-1455
We have studied the structure and magnetic properties of monodispersed Co c
luster assemblies with mean diameter, d = 6-13 nm. In these Co cluster asse
mblies, an fee phase is predominant, whereas the volume fraction of an hcp
phase increases with increasing d from 6 to 13 nm. At a thin deposition sta
ge (average thickness, t = 1 nm), Co clusters are nearly isolated. At 300 K
, they are superparamagnetic for d = 6 nm, while ferromagnetic for d = 8.5
and 13 nm. With increasing t, the superparamagnetic to ferromagnetic transi
tion is detected for d = 6 nm. For d = 6-13 nm, the magnetic coercivity, H-
c, rapidly increases at t = 2-4 nm, near or below the geometrical and elect
rical percolation thresholds. However, H-c is almost independent of t up to
t = 100 nm.