Muon Spin Depolarization in Metals with Dilute Magnetic Impurities
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MUON SPIN DEPOLARIZATION IN METALS WITH DILUTE MAGNETIC IMPURITIES
J. A. BROWN, R. H. HEFFNER, R. L. HUTSON, S. KOHN,* M. LEON, C. E. OLSEN AND H. E. SCHILLACI Los Alamos National Scientific Laboratory, Los Alamos, New Mexico 87545 S. A. DODDS, T. L. ESTLE, D. A. VANDERWATER Rice University, Houston, Texas 77001 P. 1. RICHARDS Sandia National Laboratories, Albuquerque, flew Mexico 87185 C. D. McMASTERS Iowa State University, Ames, Iowa
ABSTRACT Muon diffusion can be studied in metals without nuclear We describe moments by the addition of paramagnetic impurities. the theory and report measurements of muon depolarization in gold and silver doped with gadolinium and erbium. As well as diffusion rates, strength of the ragnetic interaction and spin lattice relaxation rate of the paramagnetic ion are inferred from the data.
INTRODUCTION One of the most active fields of study using the technique of muon spin particles in a metallic rotation (uSR) is the diffusion of light interstitial A comparison of muon diffusion with the diffusion of the heavier host lattice. hydrogen isotopes offers the possibility to study different mechanisms of particule motion; the light mass of the muon, for instance, may allow a coherent or band-like motion which is negligible for the heavier particles. Information on muon diffusion is derived from the temperature dependence of Depolarization results from interaction of the muon the depolarization rate. spin with magnetic moments of the host material, which means the nuclear spins The situation is completely in the case of nonmagnetic metals treated here. At low temperatures the analogous to that of motional narrowing [1] in NMR. muon stays at a particular site for a time long enough to precess in the local Since the local field varies from site to field characteristic of that site. site because of random orientation of the host nuclear spins, there results a spread of precessional frequencies of muons stopped at random which gives rise At higher temperatures the muon moves from site to site to the depolarization. The depolarization rate then approaches and samples many different local fields. The precise manner in which the zero as only the average local field is seen. depolarization rate decreases with temperature can be used to infer the muon hopping rate. (a) rapid muon There are, however, two limitations inherent in such studies: motion cannot be studied once the depolarization becomes vanishingly small and In (b) many host materials such as Aa and Au have negligible nuclear moments. the first case, an upper limit to the observable muon diffusion rate is reached at low temperatures; in copper no depolarization is observed at temperatures This restricts the comparison with hydrogen greater than about 240K [2]. In the latter case, no diffusion which is measured at much higher temperatures. *Present address:
University of California Lawrence Berkeley Laboratory.
410 information on muon diffusion can be obtained. These two problems can be circumvented by the introduction of small amo
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