Magnetic circular dichroism has been used to study the orbital and spin moments in supported nanoscale Fe clusters deposited in situ from a gas aggregation source onto highly oriented pyrolitic graphite in ultrahigh vacuum. Mass-filtered ͑2.4 nm, 610 atoms͒ and unfiltered ͑1-5 nm, 40-5000 atoms͒ clusters at low coverage have an orbital magnetic moment about twice that of bulk Fe. With increasing coverage the orbital moment of the unfiltered clusters converges to the bulk value. There is no detectable change in the spin moment as a function of coverage. Mass-filtered clusters show an increase in the magnetic dipole moment which we ascribe to distortion resulting from their higher impact energy. An increasing magnetic remanence with coverage is found. ͓S0163-1829͑99͒02225-0͔
The design and operation of a gas aggregation source is described. The source combines the attributes of high-temperature operation (enabling preparation of transition metal clusters), mass selection, ultrahigh vacuum compatibility, and transportability. This makes it ideally suited to in situ studies such as scanning tunneling microscope or synchrotron radiation experiments. Data are presented to illustrate the performance of the source; recent results obtained in synchrotron radiation studies are highlighted.
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PACS 12.20.Fv -Quantum electrodynamics: Experimental tests PACS 78.20.Ci -Optical properties of bulk materials and thin films: Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity) PACS 07.79.Lh -Scanning probe microscopes and components: Atomic force microscopes Abstract -We present here measurements of the Casimir force gradient in the 60-300 nm range using a commercial Atomic Force Microscope operating in Ultra High Vacuum (UHV). The measurements were carried out in the sphere-plate geometry between a Au sphere and plates consisting of two different classes of material, that is a metal (Au) and a semimetal (HOPG). The variation in the optical properties of the materials produces clearly observed differences in the Casimir force as predicted by calculations based on the quantum theory of optical networks and the Lifshitz theory.
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