Electron Energy Levels in Magnetic Nanoparticles

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W:\awards\awards97 9705059 Ralph This is a new project to study electrons confined within metal particles less than 10 nm in diameter such that the discrete "electrons-in-a-box" energy levels become resolvable at low temperatures. We have developed techniques for fabricating single-electron tunneling transistors containing an individual, nm-scale metal particle, and we have used these devices to make detailed measurements of the electronic spectrum within the nanoparticle. This new capability is a powerful probe of electronic structure, because all the forces which act on the electrons can be studied through their separate effects on the eigenstate spectrum. In this proposal, we will apply these techniques to study magnetic particles. We will (a) manipulate single quantum levels to study spin-polarized electron tunneling, (b) examine the electronic spectrum in magnetic particles to understand exchange forces and the correlated states which they produce, and (c) use time-dependent studies of level spectra as a probe of the dynamics of the nanoparticle's magnetic moment. %%% This is a new project to study electrons confined in very small metal particles. When a piece of metal is so small that it contains fewer than 10,000 atoms, the mobile electrons inside the metal cannot have any arbitrary energy, but are limited to a resolvably discrete set of states. Because of the level discreteness, electronic devices on these small length scales can be thought of as "artificial atoms". We have recently developed techniques for producing transistor devices by connecting wires to individual metal nanoparticles, and then using these devices to measure the spectrum of allowed energy levels inside the metal particle for the first time. In this proposal, we will apply these new techniques to study magnetic particles. We will examine (a) under what conditions electrons can h op on and off a magnetic particle without flipping their spin, (b) how magnetic forces alter the spectrum of electron energy levels, and (c) the mechanisms by which the magnetism of the particle may switch direction under the influence of an applied magnetic field. ***