Muon studies of low-dimensional solid state systems

Jestädt, T

Oxford Thesis Collection

Thesis

Muon studies of low-dimensional solid state systems

Abstract:: This thesis concerns the use of the technique of μSR, an abbreviation which stands for three separate types of experiments: muon spin rotation, muon spin relaxation and muon spin resonance. The experiments presented here were performed on beamlines at the ISIS facility at the Rutherford Appleton Laboratory (U.K.) and at the Paul Scherrer Institut (Villigen, Switzerland). The systems studied are linked by the common theme of reduced dimensionality.

Results of μSR measurements on La_2-xSr_xNiO_4+δ (nickelates) are presented. In these systems the lattice constants are much smaller in two of the dimensions as compared to the third, leading to two dimensional magnetism. Earlier experiments using techniques other than μSR concentrated mainly on materials with x = 0 and δ ≠ 0. The work that I describe on La_2-xSr_xNiO_4+δ shows that there are interesting magnetic features as a function of strontium doping, and the details of this dependence are examined. In each of the samples oscillations of the muon spin polarization were observed below a sample dependent temperature, showing that low temperature magnetic order occurs.

μSR is also used to study Sr₂LnMn₂O₇ (the Ruddlesden-Popper phases), where Ln are various ions of the lanthanide series. These manganates have a layered structure, leading to a reduced dimensionality as compared to the related perovskite compounds of the MnO₃ series. Like the doped MnO₃ compounds, some of the Ruddlesden-Popper phases exhibit colossal magnetoresistance (CMR), an effect which initially stirred interest in the MnO₃ systems. In contrast to the MnO₃ systems, the relevant Mn₂O₇ materials show this CMR effect over an extended temperature range. The μSR work is consistent with the existence of magnetic clusters in some of the Mn₂O₇ materials and these clusters appear to be associated with the observation of CMR.

The compound CaV₄O₉ is the first known two-dimensional compound to exhibit a spin-gap and the effects of this spin-gap on the magnetic properties are investigated here.

I also describe results of measurements on a material with even more reduced dimensionality, polybutadiene (PB). This is a non-conducting polymer without side-chains. Muons in this system can either be in a paramagnetic or a diamagnetic state (with a polymer radical state produced by reaction of muonium with a polymer bond). The nature of these states has been examined with a variety of μSR techniques, and the inuence of the polymer dynamics and the glass transition in PB is discussed.

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APA Style

Jestädt, T. (1999). Muon studies of low-dimensional solid state systems [PhD thesis]. University of Oxford.

MLA Style

Jestädt, T. Muon Studies of Low-Dimensional Solid State Systems. 1999. University of Oxford, PhD thesis.

Chicago Style

Jestädt, T. 1999. “Muon Studies of Low-Dimensional Solid State Systems.” PhD thesis, University of Oxford.
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