Daniel Tennant, UT-Austin

"Aging as a Measure of Domain Growth in Multilayer Thin Films of the Spin Glass Copper Manganese"

Abstract: This work describes two related investigations into the Spin Glass phase of CuMn multilayer thin films. In addition, the construction of and improvements on a home built SQUID magnetometer built in pursuit of these goals will be detailed. The common theme between these experiments at the mesoscale is the exploitation of the fact that the film thickness and the length scale of spin glass correlations are of comparable size. The fact that the lower critical dimension of the spin glass phase is between two and three allows a direct probe of the transition between a finite temperature phase transition and zero temperature fixed point glassy state. The time and temperature dependence of the correlation length growth as well as the energy barrier structure are explored and found to agree with the predictions of the hierarchical model of Parisi and is at odds with the droplet model of Fisher and Huse. In particular, the growth of correlations is cutoff by the finite film thickness. This results in a maximum energy barrier in configuration space dictated by the film thickness and independent of temperature. In addition, the growth of domains, or correlated regions, is explored through the waiting time effect in the Thermoremnant Magnetization decays. Aging, or the exploration of configuration space through thermally activated transitions, is shown to be directly related to the growth of domains in this disordered system.