Effects of ferromagnetic nanopillars on spin coherence in an InGaAs quantum well

Low-temperature antilocalization measurements are used to investigate the interactions between a two-dimensional electron system in an In0.53Ga0.47As quantum well in an InGaAs/InAlAs heterostructure, and the magnetic moments of CoFe nanopillars located on the heterostructure surface. With CoFe nanopillars, a decrease in spin coherence time is observed, attributed to the spatially varying magnetic field from the local moments. A good agreement between the data and calculations suggests that the CoFe nanopillars also generate an appreciable average magnetic field normal to the surface of value ~35 G at the quantum well. The measurements further show that surface metal coverage increases mobility, and for non-magnetic coverage increases spin coherence time, consistent with the Elliott–Yafet spin-decoherence mechanism. Phase coherence times decrease as the temperature decreases, consistent with phase decoherence via the Nyquist mechanism.