Influence of CoFe nanopillars on spin coherence in an InGaAs quantum well

An array of ferromagnetic (Co$_{0.6}$Fe$_{0.4}$) nanopillars was fabricated on the surface of an InGaAs/InAlAs heterostructure. The interactions between the magnetic moments of the nanopillars and two-dimensional electrons in the In$ _{0.53} $Ga$ _{0.47} $As quantum well are experimentally studied by low-temperature antilocalization measurements. The presence of ferromagnetic nanopillars increases the spin-orbit scattering rate, interpreted as due to the spatially varying nanopillar magnetic field. At the quantum well, also an appreciable average fringing field $\sim$ 35 G normal to the surface is generated by the large saturation magnetization of the nanopillars. Numerical values show a good correspondence between the analysis of the experimental antilocalization data and calculations from a simple micromagnetic model. The measurements further show an increase in mobility due to surface metal coverage. Consistently, non-magnetic coverage is observed to decrease the spin-orbit scattering rate, as expected for increased Coulombic screening under the Elliott-Yafet spin-decoherence mechanism. The analysis also shows the inelastic scattering rate increasing as temperature increases, consistent with the Nyquist mechanism. The work is supported by DOE DE-FG02-08ER46532.