Magnetic, electrical and magnetotransport properties of Cr O_2 and V O_2-based thin films and heterostructures
In this dissertation, thin films of two promising rutile oxide materials (CrO2 and VO2) are studied. Additionally, magnetic tunnel junctions (MTJs) with these two materials as ferromagnetic (CrO2) and barrier layer(VO2) are fabricated and their properties are investigated. The CrO2 thin films are successfully grown on TiO2 (001) substrates by atmospheric pressure chemical vapor deposition (APCVD). Their structural and magnetic properties have been examined. The Stoner-Wohlfarth model is used to extract the distribution of the effective anisotropy field in the CrO2 (001) films for providing a better understanding of the out-of-plane magnetic behavior. The unexpected in-plane magnetic behavior is explained by the possible existence of stripe or vortex domain structures in the films. Besides CrO2, VO2 thin films and CrO2/VO2 heterostructures have been grown on TiO2 substrates of different orientations - (100), (110) and (001) - and their electrical and magnetic properties are studied. Finally, MTJs with CrO2 as the ferromagnetic electrode, heteroepitaxial VO2 as the barrier layer, and Co as the counter electrode are fabricated, and their transport and magnetic properties are investigated. The bias, temperature and barrier thickness dependence of the tunneling magnetoresistance (TMR) of these CrO2/VO2-based MTJs are presented. The Simmons and Brinkman models are used to estimate the barrier height of the tunneling device. In addition, the magnetic behavior of the MTJs at different temperatures is studied.