Abstract
The metastable magnetic alloy Co
10
Cu
90
has been prepared by the conventional melt-spinning technique. The rapid solidification process results in an extended solubility of Co in Cu although some Co particles already have precipitated during quenching. In comparison with conventional ageing methods, Joule heating could also be adopted to fabricate granular Co-Cu alloys with even finer Co particles. The finest size of 4.0nm has been achieved for Co
10
Cu
90
alloy after annealing with a current I = 4 A for 1 rnin. Single-domain behaviour results in a value of coercivity in excess of 40.0 kAm
−1
for the sample annealed with I = 9.5 A. Below the size of 6.0 nm, Co particles exhibit superparamagnetic behaviour at room temperature, which has been investigated using a superconducting quantum interference device magnetometer. A unique change in M
s
with annealing current or temperature was discovered.