Spin Coupling and Orbital Angular Momentum Quenching in Free Iron Clusters

Abstract

Magnetic spin and orbital moments of size-selected free iron cluster ions Fe{n}{+} (n=3-20) have been determined via x-ray magnetic circular dichroism spectroscopy. Iron atoms within the clusters exhibit ferromagnetic coupling except for Fe{13}{+}, where the central atom is coupled antiferromagnetically to the atoms in the surrounding shell. Even in very small clusters, the orbital magnetic moment is strongly quenched and reduced to 5%-25% of its atomic value while the spin magnetic moment remains at 60%-90%. This demonstrates that the formation of bonds quenches orbital angular momenta in homonuclear iron clusters already for coordination numbers much smaller than those of the bulk.

Spin and orbital magnetic moments of size-selected iron, cobalt, and nickel clusters

“…Even though the line shape is almost bulk-like, the line width 53,63,69 is narrower for the clusters investigated here. In addition to the x-ray absorption spectra, two step functions are shown in Fig.…”

Electronic ground states of Fe2+ and Co2+ as determined by x-ray absorption and x-ray magnetic circular dichroism spectroscopy

“…The most intense product ion that results from 2p core excitation and relaxation is the atomic dication for both Fe For XMCD spectroscopy, the ion trap is placed inside the homogeneous magnetic field (µ 0 H = 5 T) of a superconducting solenoid. [35][36][37][38][39][40]44 Following the standard procedures, the XMCD spectrum is obtained as the difference of x-ray absorption spectra that are recorded with parallel and antiparallel orientation of the photon helicity relative to the direction of the applied magnetic field. The isotropic x-ray absorption spectrum is obtained by taking the average of the spectra of both photon helicities.…”

“…In particular for free as determined by gasphase x-ray magnetic circular dichroism (XMCD) spectroscopy [34][35][36][37][38][39][40] that was only recently introduced for free molecular ions. 39,40 All states that are found in our study carry significant orbital angular momentum that disagrees with theoretical preferences for Σ states.…”

Size-dependent Auger spectra and two-hole Coulomb interaction of small supported Cu-clusters

“…Core-level photoelectron spectroscopy is a surface sensitive and element specific tool which can be applied to study highly diluted samples such as free and deposited clusters by X-ray photoelectron spectroscopy (XPS), [1][2][3][4][5][6][7][8][9] X-ray absorption spectroscopy (XAS) [10][11][12] , extended X-ray absorption fine structure analysis (EXAFS), 13 grazing-incidence small-angle X-ray scattering (GISAXS), 14 X-ray magnetic circular dichroism (XMCD) [15][16][17] and Auger electron spectroscopy (AES). 18 In particular AES and XPS provide information on the initial and final states such as chemical effects, charge transfer, core-hole screening, core-hole binding energies, and electron correlation including final-state term splitting and on-site electron-electron interaction.…”