Synchrotron radiation studies of mass-selected Fe nanoclusters deposited in situ

Abstract

A portable UHV-compatible gas aggregation cluster source, capable of depositing clean massselected nanoclusters in situ, has been used at synchrotron radiation facilities to study the magnetic behaviour of exposed and Co-coated Fe clusters in the size range 250 to 540 atoms. X-ray magnetic circular dichroism (XMCD) studies of isolated and exposed 250-atom clusters show a 10% enhancement in the spin magnetic moment and a 75% enhancement in the orbital magnetic moment relative to bulk Fe. The spin moment monotonically approaches the bulk value with increasing cluster size but the orbital moment does not measurably decay till the cluster size is above ∼ 400 atoms. The total magnetic moments for the supported particles though higher than the bulk value are less than those measured in free clusters. Coating the deposited particles with Co in situ increases the spin moment by a further 10% producing a total moment per atom close to the free cluster value. At low coverages the deposited clusters are superparamagnetic at temperatures above 10 K but a magnetic remanence at higher temperature emerges as the cluster density increases and for cluster films with a thickness greater than 50Å (i.e. 2-3 layers of clusters) the remanence becomes greater than that of an Fe film of the same thickness produced by a conventional deposition source. Thick cluster-assembled film show a strong in-plane anisotropy.

Orbital contribution to the magnetic properties of iron as a function of dimensionality

“…Such experiments have been carried out by Gambardella et al [5,6] who have indeed measured orbital moments as large as 0.68µ B for Co chains on Pt(997) and 1.1µ B for a Co adatom on Pt(111), the corresponding MAE being 2meV and 9meV per Co atom, respectively. Moreover XMCD experiments carried out on iron clusters [7,8] have shown that the orbital moment is much more enhanced than the spin moment as the size is reduced.…”

Experimental Demonstration of a Ring-Cavity Q-Switched Fiber Regenerative Amplifier

“…An example of mass spectra obtained at two different pressures is shown in figure 1, which also displays an in situ STM image obtained in a previous study of unfiltered Fe clusters deposited on Si(111) under similar preparation conditions. It has been verified that, in the case of Fe clusters, the mass distribution measured in the free cluster beam is unchanged after depositing on a substrate [18] or embedding in a matrix [11]. The mass spectra show the expected log-normal shape and the curves in figure 1 are optimized fits as a function of the mean size ( n ) and the standard deviation (σ ).…”

State-specific RKKY interaction in small magnetic clusters

“…1,2 Owing to the fact that a major factor controlling the OMM is the spin-orbit (SO) interaction, 24 considerable efforts have been devoted to producing nanograins made of magnetic materials with large magnetic moments, large SO coupling, and large magnetic anisotropy energy. [3][4][5][6][7][8][9][10][11][12][13] Thus, investigations of magnetic nanograins consisting of elemental or binary clusters based primarily on the TM atoms such as Co, Fe, and Ni have been attempted. In the case of binary grains the second material can be a metal (TM, Cu, Ag, Au), a semiconductor (C, Si), or a rare earth (Sm).…”