Small binary iron‐carbon clusters with persistent high magnetic moments. A theoretical characterization

Abstract

Characterization of the structural and electronic properties of binary iron‐carbon clusters composed by six iron atoms and with up to nine carbon atoms was carried out with density functional theory calculations. Neutral, cations (q = +1), and anions (q = −1), some of them experimentally detected, were studied. The formation of dimers and trimers of carbon atoms over the iron surface were preferred. Moreover, some large carbon chains, with up to five atoms, were determined. High spin states emerged for the ground states, with multiplicities above 16, for all clusters independently of the number of carbon atoms attached to the iron core. All neutral clusters were stable because fragmentation (into carbon chains), dissociation (of a single carbon atom), and detachment of all carbons need high amounts of energy. Reactive species were defined by small HOMO‐LUMO gaps. Charge transfer, to the carbon atoms, increased as the carbon content increased, producing, for some cases, an even‐odd behavior for the magnetic moment of the Fe6Cn particles.

Synthesis and magnetic properties of sub-nanosized iron carbides on a carbon support

“…48 Additionally, the density functional theory studies have reported that the iron carbide clusters show the magnetic moment of ca. 1-3.5 m B atom Fe À1 , [30][31][32] which is consistent with those in this study. Therefore, with consideration of the magnetic moment and the Curie temperature, it was concluded that the magnetic behavior of the iron carbide cluster samples is derived from the carbides themselves, and not from impurities.…”

“…2 nm, 7,16 aside from the gas phase experiments 26,27 and the theoretical studies. [28][29][30][31][32] In these cases, the iron carbide nanoparticles exhibit superparamagnetism, i.e., they do not act as magnets at ambient temperature. However, sub-nanosized iron carbide particles have remained elusive to date.…”

“…S3a †) 40 as well as the theoretical studies. [28][29][30][31][32] It should be noted that atomic-resolution images that would project the clusters could not be obtained, because these samples exhibit ferromagnetism, even at room temperature (vide infra).…”

Characterization of Magnetic Series of Iron–Carbon Clusters FenC0,±1 (n ≤ 13)

“…50 Persistent high magnetic moments have already been reported for mixed iron−carbon clusters. 49 For instance, Nash et al 22 studied FeC 1−3 neutral species within DFT, at the local density approximation, and fourth-order Møller− Plesset perturbation theory. Independently of the number of carbon atoms bonded to iron, FeC 1−3 clusters are found with triplet and quintet multiplicities and, consequently, magnetic moment comparable to that found for iron in its atomic ground state.…”

“…52 From all of the above, this work aims, based on previous studies about small pure iron 3 and iron−carbon clusters, 9,51 to extend the knowledge on mixed iron−carbon clusters. In this sense, density functional theory (DFT) calculations have proven 49,51 to provide reliable results, being comparable to the most expensive wavefunction-based quantum chemistry methods. 15 2.…”