Spin Filtering of Hot Holes in a Metallic Ferromagnet

Spin-dependent transport of nonequilibrium holes in ferromagnetic thin films and trilayers is investigated using ballistic hole magnetic microscopy. For Co, the hole attenuation length is short and increases from 6 to 10 A in the energy range 0.8 to 2 eV. The hole transmission of a Ni(81)Fe(19)/Au/Co trilayer is clearly spin dependent, resulting in a surprisingly large current change by a factor of 2.3 in a magnetic field. The energy and spin dependence of the hole transmission cannot be explained by the phase space available for inelastic decay of the hot holes.