Morphological and magnetic characteristics of monodispersed Co-cluster assemblies

Abstract

Structural and magnetic characteristics of monodispersed Fe and oxide-coated Fe cluster assemblies Enhancement of magnetic coercivity and macroscopic quantum tunneling in monodispersed Co/CoO cluster assemblies Appl.Co-cluster-assembled films have been prepared using a size-controllable cluster beam deposition system, by which monodispersed Co clusters with a mean diameter, dϭ6 -13 nm are available. Their morphology and magnetic properties have been studied by scanning electron microscopy ͑SEM͒, small-angle x-ray scattering ͑SAXS͒ and magnetization measurements. The SEM images show that the film has a porous structure consisting of fine grains without a columnar texture and its density is about 25% of the bulk Co. The SAXS measurements indicate that monodispersivity of the incident clusters is maintained through their assembling process only for dϭ13 nm. All the specimens exhibit ferromagnetic behavior at room temperature and the magnetic coercive field H c rapidly increases with decreasing temperature: H c ϭ168 kA/m ͑2.1 kOe͒ at 5 K. Such an enhancement in H c is ascribed to the exchange anisotropy which arises from the antiferromagnetic Co-oxide layers covering the Co clusters, and to the assemblies of single-domain ferromagnetic clusters with the structure modification and magnetic interaction among them. The monotonic increase in H c at 300 K with increasing d is simply understood in terms of the single-domain particle theory.

Morphology and Magnetic Properties of Fe and Al Nanocomposites Prepared with Single and Double-Glow-Discharge Sources

“…The background vacuum condition of the present PGCCD system was about 0.1 Pa owing to the usage of a mechanical booster pump for evacuating a large amount of Ar gas to get a high speed viscous flow. Since it is about three orders of magnitude worse than the previous experiment, 2,21,28) the oxidation of clusters is plausible in the present PGCCD system and Al clusters are more easily oxidized than Fe clusters. 20) Since Fe and Al-oxide are immiscible each other, 29) Fe particles are covered by small Al-oxide clusters in the double glow discharge sources experiments.…”

“…30,31) Since the irregular interfaces between Fe cores and -Fe 2 O 3 shells give rise to random magnetic anisotropy which disturbs the alignment of magnetic moments of Fe cores along the applied field direction. 23,28,30,31) The magnetization curves at 5 and 300 K in Fig. 7(c) indicate that the Fe/Al cluster composite prepared using double glow discharge sources is ferromagnetic because it consist of Fe cores covered with Al and/or Al-oxide shells.…”

Electrical Percolation during Codeposition of Fe and Si Clusters by a Dual Source PGCCD System

“…Since the packing density 30-35% for the assemblies of Cr, Co, and Fe clusters prepared by previous PGCCD systems, 15,16) we assume p ¼ 0:3 for estimating the volume fraction of Fe clusters, f Fe . Figure 8 shows the values as a function of f Fe , derived from Fig.…”

High Frequency Magnetic Property of Dense Fe<SUB>22</SUB>Ni<SUB>78</SUB> Cluster Assembled Films

“…We investigate their structure, morphology, and static and high-frequency magnetic properties through measurements by transmission electron microscope (TEM), electrical resistivity, superconducting quantum interference device (SQUID) magnetometer and high-frequency permeameter. Figure 1 shows a schematic drawing of the plasma-gascondensation cluster deposition (PGCCD) apparatus, 3,12,13) which is a combination of sputter vaporization and inert-gas condensation techniques. Using this apparatus, we could control cluster size between 5 to 15 nm in diameter by adjusting the sputtering power and gas pressure (see Fig.…”

“…2) In cluster assembled films where spherical or polyhedral clusters are generated in gas phases and randomly deposited on substrates to form their porous stacks, 2,3) is two order larger than that of bulk materials, 4) M S is low, while the magnetic coercivity, H C , is rather high (a few tens kA/m) due to magnetic anisotropy of single domain particles and interparticle dipole interactions. 3,5) Material density can be improved by energetic deposition of clusters, where electrically charged clusters impinge on electrically biased substrates. High-density Fe, Fe-Co and FeNi cluster assembled films thus obtained reveal a high cluster packing density of about 85%.…”