Structures and magnetic properties of small [Formula: see text] and Co Cr (n = 3-5) clusters.

Small cobalt clusters [Formula: see text] and their single chromium atom doped counterparts Co Cr (n  =  3-5) were studied mass spectrometrically by measuring the infrared multiple photon dissociation (IRMPD) spectra of the corresponding argon tagged complexes. The geometric and electronic structures of the [Formula: see text] and Co Cr (n  =  3-5) clusters as well as their Ar complexes were optimized by density functional theory (DFT) calculations. The obtained lowest energy structures were confirmed by comparing the IRMPD spectra of [Formula: see text] and [Formula: see text] (n  =  3-5, m  =  3 and 4) with the corresponding calculated IR spectra. The calculations reveal that the doped Co Cr clusters retain the geometric structures of the most stable [Formula: see text] clusters. However, the coupling of the local magnetic moments within the clusters is altered in a size-dependent way: the Cr atom is ferromagnetically coupled in CoCr and CoCr, while it is antiferromagnetically coupled in CoCr.