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Surface and interface properties of CrO2 thin films
CrO2 has been considered as an attractive material for spin-polarized tunnel junctions and other magnetoresistive devices due to its high spin polarization. Evidence of very high polarization of 80 to 96% has been observed in spin-polarized photoemission, vacuum tunneling, and Andreev scattering. However, the spin polarization of the tunneling current in the tunnel junctions does not rely on the property of the ferromagnet alone but depends on the entire junction including the insulator and the interface between ferromagmet and insulator. Studying the electronic properties of the interface properties is particularly important to better understanding the magnetic tunnel junction. In this dissertation, both the surface and interface properties of CrO2 films are studied by using a variety of surface sensitive techniques. ^ CrO2 thin films were fabricated by using several different approaches. The angle resolved x-ray photoemission spectroscopy (ARXPS) data suggest that the Cr2O3 is the stable native surface of CrO2 thin films. Spin polarization of the conduction bands for Cr2O3 overlayer on CrO2 thin films was measured using spin-polarized inverse photoemission (SPIPES). The measured temperature-dependent spin polarization data indicate that the polarization of Cr2O 3 overlayer is mediated by gap states or defects states whose mobility increases with increasing temperature. Spin integrated inverse photoemission spectra (IPES) reveal evidence of transport involving defect states similar to electron mobility through the insulator mediated by defects. In order to investigate the interface properties between CrO2 and the related insulating barrier layer, we evaporate Co thin films on top of CrO2 films. In situ x-ray photoemission study shows Co is oxidized at the interface between Co and Cr2O3 and in situ MOKE was utilized to study the magnetic coupling of ferromagnetic-paramagnetic-ferromagnetic trilayer samples. The Co thickness-dependent and the temperature-dependent magnetic coupling were observed and the coupling through the insulating barrier could be related to the defect states in the barrier. ^
Physics, Condensed Matter
Cheng, Ruihua, "Surface and interface properties of CrO2 thin films" (2002). ETD collection for University of Nebraska - Lincoln. AAI3074071.