Electronic states in magneto-transport by photoemission

Spin-polarized transport is expected to be a driving force behind development of a new generation of electronics. Oscillatory magnetic coupling, giant magnetoresistance (GMR) and spin-polarized tunneling are three physical phenomena that either have already been used in electronics, or show potential for being exploited in devices. With that in mind, it seems important to be able to identify the electron states and properties that have the largest effects on these phenomena and magneto-transport in general. Angle-resolved photoemission is uniquely able to select well-defined spin and momentum states for study.; In a series of experiments performed at the Synchrotron Radiation Center, angle-resolved photoemission and high quality single crystal samples were used to investigate three properties of magnetic systems which provide insight into magnetic coupling, GMR and spin-polarized tunneling. Photoemission from Cu on Co quantum well states indicated that the reflection of electrons at the interface between two metals can be spin dependent. Analysis of the momentum broadening of high resolution photoemission data from Ni and Ni alloys allowed the extraction of the mean free path length in these materials. The magnitude of the giant magnetoresistance effect depends on these path lengths. It was further found that by mixing various impurities into Ni, the spin-dependence of the mean free path could be adjusted. For example, iron suppresses the mean free path of minority spins only, while chromium suppresses both spins. In addition, high resolution photoemission also allowed examination of the spin-polarization of states at the Fermi level, and lead to a conclusion that the matrix element might be responsible for excess spin-polarization seen in Ni during tunneling experiments. Finally, in what is perhaps a more traditional role for photoemission, the band structure of technologically important permalloy (Ni_0.8Fe_0.2) was mapped, providing data for theories on the mixing of Ni and Fe states in alloys.