Physics and Astronomy, Department of

 

Date of this Version

Summer 7-29-2013

Comments

A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Physics and Astronomy, Under the Supervision of Professor David J. Sellmyer and Professor Ralph Skomski. Lincoln, Nebraska: July, 2013

Copyright (c) 2013 Rui Zhang

Abstract

Three systems involving low-dimensional magnetic nanostructures, namely the Kondo Effect in Isolated Cu(Fe) Clusters, Magnetization Reversal in Transition-Metal/Fe:SiO2 Thin Films, and Anisotropy and Micromagnetism of Fe/CrPt Bilayers, have been investigated to understand the magnetic interactions in iron nanostructures.

Kondo Effect in Isolated Cu(Fe) Clusters —Iron impurities were added into copper clusters embedded in an insulating matrix to ensure that the Kondo effect is strictly confined by the size of the cluster. The Kondo temperature of our naoscale system is 0.7 K, which is greatly suppressed from its bulk value of 29 K and is consistent with our theory prediction. This approach offers a new angle to experimentally probe the Kondo screening cloud.

Magnetization Reversal in Transition-metal/Fe:SiO2 Thin Films —A novel way has been proposed to improve the performance of the soft-magnetic layers via magnetostatic interactions through iron clusters. All tested soft magnetic materials showed clear signs of coercivity reduction and for certain materials, such as Co-Fe-B, the permeability was also improved by factors of up to 5. This method opens up a new path towards the design of free layers used in magnetic tunneling junctions and spin-valve structures.

Anisotropy and Micromagnetism of CrPt / Fe Bilayers —Iron thin films, exchange-coupled to an adjacent antiferromagnetic CrPt layer, have been used as a probe to measure the anisotropy of L10-ordered CrPt. The alloy is of interest as a replacement for the Mn-based antiferromagnetic layers in magnetic tunneling junctions, but its anisotropy has been largely underestimated due to the complications introduced by magnetic annealing. The estimated value from our methods is -438 kJ/m3, which is much closer to its theoretical prediction than values obtained by other experimental methods.

The present findings have several scientific and technologic implications, as described in the main part of the thesis.

Advisor: David J. Sellmyer and Ralph Skomski