On the direct magnetic detection of spin injection and adiabatic depolarization in aluminum

An attempt has been made to measure directly the magnetic field created by the spin polarization injected into polycrystalline aluminum from iron injection electrodes in a geometry optimized with respect to a particular SQUID-based second-order gradiometer. Magnetizations, as low as 1 A/m, are detected independently of the influence of the ferromagnetic injectors and applied current densities of the order of 108 A/m2. The current induced changes in magnetic response are analyzed in terms of components of the coupled to the gradiometer flux, symmetric, anti-symmetric and asymmetric in current and in space, including: mutual inductance, induced spin polarization, adiabatic electronic depolarization and lattice heating effects. No evidence for induced spin polarization is found down to a spatial resolution of 1 mm and temperatures of 1.8 K for applied fields in the range 20-500 mT.