Doctor of Philosophy (Ph.D.)
For the first time, external uniaxial stress has been used in a (mu)('+)SR experiment. The stress dependences of the following parameters were obtained for Fe crystals: the muon precessional frequency, (nu)(,(mu)), the transverse (longitudinal) depolarization rates, 1/T(,2) (1/T(,1)), and F(,T)/F(,L), the ratio of the probabilities for the muon to find domains with transverse/longitudinal fields. The shift in (nu)(,(mu)) was -0.34 (+OR-) 0.023 MHz per 100 micro-strain along the -axis. Changes in other parameters depend on the sample history but they, in general, increase with stress.;External stress changes the muon occupational probability at each site which significantly affects the dipolar field averaged over interstitial sites of the same initial symmetry. This change in the averaged dipolar field is shown to be the main cause of the shift in (nu)(,(mu)). to calculate the dipolar field at each site, the finite extension of the muon probability density and displacement of neighboring host atoms around the site are explicitly taken into account. From the experimental results and the dipolar field calculation, it is possible to estimate the anisotropy of the double-force tensor, (P(,1)-P(,2)), for the muon in Fe. This clearly shows that in Fe, for reasonable muon wave function shapes, the muon is more likely to occupy the 4T(0) site configuration.;For a random distribution of domains among the six easy axes of Fe, the dipolar field averaged over a region of the sample should be zero. However, the external stress breaks this randomness and with a certain magnitude of tensile stress in the z-axis, domains will align along the (+OR-) z-directions. A muon with its initial spin aligned perpendicular to the z-axis does not distinguish the stress induced domain alignment from the saturation along the + or - z direction. The experimental result shows the same stress dependence of (nu)(,(mu)) for both the stress induced and the externally saturated domain alignments. as expected the change in (nu)(,(mu)) with low stress is very small without the application of an external saturation field. Also, the change in F(,T)/F(,L) is consistent with that in (nu)(,(mu)) indicating that this parameter is a good measure of the domain alignment.;Similar results were obtained for polycrystalline samples. The interpretation made on the single crystal result is applicable to these results and it is possible to explain why local strains in Fe tend to reduce the magnitude of (nu)(,(mu)).
© The Author
Namkung, Min., "A [mu]+SRstudy of uniaxial stress induced symmetry breaking in an Fe single crystal" (1982). Dissertations, Theses, and Masters Projects. Paper 1539623735.