Doctor of Philosophy (Ph.D.)
Positive muons implanted in metal distort the surrounding lattice; therefore, in addition to electronic interactions, the elastic forces have to be considered in determining the muon state. to explore the elastic and electronic diffusion and trapping mechanisms, we studied AlCu(,420ppm), AlMg(,1000ppm) and AlAg(,1000ppm) alloys. These alloys were selected for the different effects on the host lattice of these impurities; Cu contracts the Al lattice, Mg expands it and Ag has nearly no effect. On the other hand Cu and Ag are monovalent while Mg is divalent. For AlCu between 5K and 14K the temperature exponent (beta) of the two-state-model trapping rate ((nu)(alpha)T('(beta))) was 0.93 (+OR-) .26 for zero field and 1.16 (+OR-) .14 for a 14.2G longitudinal field. A (beta) of 1 implies a one phonon induced diffusion process. For AlMg the transverse field (150G) second moment of the static random fields was 0.317 (+OR-) .007 (mu)s('-1) between 10K and 60K, 0.221 (+OR-) .013 (mu)s('-1) between 60K and 150K and 0.150 (+OR-) .013 (mu)s('-1) between 150K and 300K. The changing value of the second moment indicates a change in the muon trapping site from tetrahedral to octahedral to vacancy as the temperature is increased, this was confirmed at appropriate temperatures by zero and longitudinal field studies. Comparing the AlMg results with earlier work on AlCu two types of trapping sites can be identified, those dependent on the magnitude but not sign of deformation, and thought to be a few atomic distances away from the defect, and those which are possibly close to Mg. For AlAg, since Ag has almost no elastic effect the weaker depolarization structure suggests a different trapping mechanism, possibly due to the electronic interaction. to study the muon interaction with a uniform strain field, uniaxial stress was applied to an Fe (3 wt. % Si) single crystal. We measured the temperature dependence of the frequency shift versus strain to be -0.348 (+OR-) .007 MHz/100(mu)(epsilon) (25.7 (+OR-) .5 G.100(mu)(epsilon)) at 300K and -0.279 (+OR-) .010 MHz/100(mu)(epsilon) (20.6 (+OR-) .7 G/100(mu)(epsilon)) at 360K. The agreement of the room temperautre result with earlier work on pure Fe shows that these shifts are inherent to Fe and not impurity dependent. That the shifts are proportional to (1/T) confirms that these effects are dominated by a strain-induced-muon-population shifts between crystallographically equivalent but magnetically inequivalent sites.
© The Author
Hitti, Bassam Salim, "Effect of strain on muon diffusion and trapping in metal by Bassam Salim Hitti" (1986). Dissertations, Theses, and Masters Projects. William & Mary. Paper 1539623760.