PNNL

Abstract

Multilayers of Co and ZnO, with nominal layer thicknesses on the atomic scale with up to 25 bilayers, were deposited by ion beam sputtering on silicon and glass substrates at ambient temperature. Thick epitaxial CoxZn1-xO films on A12O3(012) substrates were grown by metalorganic chemical vapor deposition using a liquid precursor delivery system. All were co-doped with A1. Comparative analysis of magnetization, resistivity, and magnetoresistance measurements, performed in the temperature range 2.5-300K, is presented. At small thickness of Co layers in the multilayer samples, these structures are diluted magnetic semiconductor (DMS) superlattices, with properties close to the epitaxial films. A crossover from DMS to discontinuous magnetic metal/semiconductor multilayers is observed with increasing metal content in the multilayers. This leads to changes in conduction mechanisms, with increasing contribution of quasi-three-dimensional or quasi-two-dimensional inter-granular hopping, and superparamagnetism.