Matrix effect on the magnetic properties of cobalt nanoclusters

We produced cobalt nanoclusters by thermally decomposing Co ₂(CO) ₈ carbonyl in a gas phase and in mineral oil (i.e., oil matrix) and investigated their magnetic properties. We observed that size distributions, structures, and resulting magnetic properties were affected by the oil matrix. Both nanoclusters produced in the gas phase (NGP) and in mineral oil (NMO) consisted of small superparamagnetic nanoclusters at room temperature with particle sizes of 2.5 - 6.5 and 2.0 - 6.0 nm for NGP and NMO, respectively, and large ferromagnetic nanoclusters with particle sizes of 10 - 35 and 10 - 25 nm for NGP and NMO, respectively. An X-ray diffraction (XRD) study showed that NMO mostly consisted of a face centered-cubic (fcc) structure due to the effect of the oil matrix whereas NGP consisted of both fee (major structure) and hexagonal closely packed (hcp) structures. We observed large coercivities which ranged from 280 to 800 Oe and from 600 to 1100 Oe for temperatures from 3 to 300 K for NMO and NGP, respectively, and high saturation magnetizations which ranged from 108 to 114 emu/g and from 103 to 106 emu/g for temperatures from 3 to 300 K for NMO and NGP, respectively.