Geometric, electronic, and magnetic structure ofFexOy+clusters

Abstract

Correlation between geometry, electronic structure and magnetism of solids is both intriguing and elusive. This is particularly strongly manifested in small clusters, where a vast number of unusual structures appear. Here, we employ density functional theory in combination with a genetic search algorithm, GGA+U and a hybrid functional to determine the structure of gas phase Fe In nano technology there is an ever increasing demand for increasing the density of electronic and magnetic devices. This continuous downscaling trend drives the interest to electronic and magnetic structures at the atomic scale. In essence, two things are required: first, novel materials and building blocks with exotic physical properties. Second, a fundamental knowledge of the physical mechanism of magnetism at the sub-nanometer scale.Atomic clusters, having highly non-monotonous behavior as a function of size, are a promising model system to study the fundamentals of magnetism at the nanoscale and below. Such clusters consist of only tens of atoms. Quantum mechanics starts to play an essential role at this small scale, adding extra degrees of freedom. Since these clusters are studied in high vacuum, they are completely isolated from their environment.To use these clusters as a model system, as a starting point, a detailed understanding of the relation between their geometry and electronic structure is required.Even in the bulk, iron oxide has a wide variety of chemical compositions and phases with many interesting phenomena, such as the Verwey transition in magnetite. 1,2Experiments performed on small gas phase Fe x O y clusters beyond the two-atom case are scarce. The structure of one and two Fe atoms with oxygen has been studied in an argon matrix using infrared spectra.3,4 The corresponding vibration frequencies have been identified using density functional theory (DFT).Iron-oxide nanoparticles have been investigated for their potential use as catalyst in chemical reactions.5 Furthermore, since the iron-oxygen interaction has a fundamental role in many chemical and biological processes, there have been quite some studies, both experimental and theoretical, of the chemical properties of Fe x O y clusters. 6-12The possible coexistence of two structural isomers for stoichiometric iron-oxide clusters in the size range n ≥ 5 was experimentally measured using isomer separation by ion mobility mass spectroscopy for Fe n O n and Fe n O n+1 (n = 2-9).13 Furthermore, the formation of Fe x O y clusters has been studied in the size range (x = 1-52). 14The number of theoretical studies is, however, manifold. The magic cluster Fe 13 O 8 was extensively studied and identified as a cluster with C 1 but close to D 4h point group symmetry.15-19 However, also the geometry and electronic structure of other cluster sizes have been studied theoretically.15,20-25 The prediction of geometric structures requires a systematic search of the potential energy surface to find the global minimum.The majority of theoretical studies were performed using DFT. 4,6,9,1...

Nonconventional screening of the Coulomb interaction in FexOy clusters: An ab initio study

“…For example, from a comparison of the experimental vibrational spectrum with the theoretical spectra of different isomers and magnetic structures, the geometric and magnetic structure are obtained in good agreement with the experiment. 12,14…”

Exchange interactions in transition metal oxides: the role of oxygen spin polarization

“…[61] Furthermore, the proposed approaches can also be used to test the validity of the Heisenberg model used in atomistic spin dynamics simulations, where spin polarization on exchange-mediated ligands is often neglected.…”

High-temperature expansion method for calculating paramagnetic exchange interactions

“…The theoretical interest in these systems is due to the synthesis and study of the magnetic properties of the molecular magnets with ring geometry. [28][29][30][31] Such systems demonstrate a number interesting and complex phenomena, quantum spin tunneling, long-time spin relaxation, topological spin phases (Berry phases) and others. In this respect the microscopic understanding of the intra-molecular magnetic couplings plays a crucial role.…”