Contributions to Hanle lineshapes in Fe/GaAs nonlocal spin valve transport

The transport Hanle effect is commonly used to determine spin lifetimes in spin-polarized transport structures. We show that the domain structure of ferromagnetic contacts used to inject and detect the spin current introduces asymmetries to the Hanle lineshape. In addition, the nuclear spin polarization can produce anomalous narrowing and broadening of the Hanle linewidth depending upon the orientation of the transport spin and the applied field. Neither effect is included in the analysis typically applied. We illustrate how these contributions can significantly impact the apparent spin lifetime extracted from the transport Hanle lineshape, and how they can be compensated for.