Rare earth paramagnetism,as studied by μSR |
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Authors: | Erik B Karlsson |
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Institution: | (1) Dept. of Physics, University of Uppsala, Box 530, S-75121 Uppsala, Sweden |
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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. |
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Keywords: | |
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