Nanoscale CoPt grains were prepared within protein shells from aqueous reac
tants, A series of particles with varying Co:Pt ratios was used to explore
the transition from superparamagnetic to ferromagnetic behavior at room tem
perature. TEM and electron diffraction confirmed ordered fct CoPt phases wi
th an average grain size of 4.1 nm, Magnetic characterization was performed
at room temperature using VSM. The use of this system to prepare high-dens
ity recording media is discussed.