Structures and magnetic properties of small Co_n ⁺} and Co_n-1Cr⁺ (n = 3-5) clusters

Small cobalt clusters Co+n and their single chromium atom doped counterparts Con-1Cr+(n = 35) 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 Co+n and Con-1Cr+ (n = 35) 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 ConAr+m and Con-1CrAr+m (n = 35, m = 3 and 4) with the corresponding calculated IR spectra. The calculations reveal that the doped Con-1Cr+ clusters retain the geometric structures of the most stable Co+n 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 Co2Cr+ and Co3Cr+, while it is antiferromagnetically coupled in Co4Cr+.