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Rare earth paramagnetism, as studied by μSR (1991)

Karlsson, Erik B.

Springer

Hyperfine interactions 64 (1991), S. 331-349

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ISSN: 1572-9540

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract Some recent result of muon spin relaxation measurements in rare earth metals and intermetallic compounds are reviewed. Special emphasis is put on measurements that relate to the properties of correlated regions of spins existing relatively far above the ordering temperature in the rare earth ions. As far as comparable data from paramagnetic neutron scattering exist, they will be discussed in the same framework. For each temperature the correlated regions (or short-lived magnetic clusters) are characterized by their size, possible anisotropy with respect to the crystalline axes and their lifetime. The actual form of the interaction between the rare earth spins themselves and with the crystal fields determine the temperature dependence of these properties; a strong dipole interaction can, for instance, be expected to change the critical behaviour nearT c . Much of the time will be devoted to experiments on Gd-metal where there are experimental indications that several interesting phenomena occur: (1) a strong effect of a cross-over from a non-conserved dynamics (dipolar) regime to a conserved (exchange dominated) regime some 10 K aboveT c , (2) an anisotropy of the magnetic clusters with respect to the hexagonalc-axis, and (3), a persistence of spin correlations far aboveT c . Some attempts to correlate the rare earth spin relaxation times measured in this region with cluster lifetimes deduced from neutron scattering will be reviewed, as well as a model for understanding these lifetimes in terms of temperature dependent cluster wall motion, which is determined by exchange and magnetic anisotropy parameters. Effects of possible quantum correlations originating from the “spin system+bath” interaction will be mentioned.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02396160

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Electronic Resource

Recent progress in the understanding of light particle tunneling in metalsDedicated to Professor Ivar Waller. (1989)

Karlsson, Erik B.

New York, NY : Wiley-Blackwell

International Journal of Quantum Chemistry 35 (1989), S. 779-791

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ISSN: 0020-7608

Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: Light positive particles can be introduced in metallic lattices where they take up interstitial positions. The motion of particles between these sites is usually described as a phonon-assisted tunneling process, which at high temperatures approaches a classical over-barrier jump motion.The present paper reviews briefly the study of such phenomena at very low temperatures where phonon assistance is no longer effective. Experiments on proton transfer between certain sites in niobium metal and on positive muons which diffuse in copper or aluminium lattices show unusual temperature dependencies, which have been explained quantitatively with recent tunneling theories. These approaches take into account the simultaneous dissipation of energy to the electron bath, a phenomenon which was shown by J. Kondo to be determined by the screening electrons following the particle. The temperature dependence is essentially an effect of the Fermi distribution of the conduction electrons. The interaction of the particle with the itinerant electrons will also determine whether the particle wavefunction will be localized or form an extended (Bloch-like) state.

Additional Material: 5 Ill.