CoCr binary nanocluster wires: Enhanced magnetic properties of the Co-rich phase

We report fabrication of CoCr binary nanocluster wires (NCWs) by thermally decomposing Co₂(CO)₈/Cr(CO)₆ metal carbonyl vapors by using a resistive heater placed in the middle of a pair of permanent disk magnets. In general, NCWs grow through the pile-up of binary CoCr nanoclusters perpendicularly to the substrates attached to the magnet surfaces. NCWs, ranging from 10 to 20 nm in diameter and also branching out while they grow, exist as a bundle. The bundles with lengths up to 2-3 mm form a three-dimensional array. We observed much higher coercivities and larger remanences for arrays with magnetic field applied parallel to the NCWs than those with magnetic field applied perpendicular to the NCWs. Importantly, we observed that arrays of CoCr NCWs with a 0.8-2.2 mol % Cr in which only Co-rich phase exists showed enhanced magnetic properties, that is, nearly doubled coercivities compared to that of the array of pure Co NCWs. When the Cr mole percentage is above 2.2, however, coercivities decreased because the amount of nonmagnetic Cr-rich phase increased accordingly.