Abstract
A quantum-statistical theory of spin-dependent tunneling through asymmetric magnetic double-barrier junctions is presented which describes both ballistic and diffuse tunneling by a single analytical expression. It is evidenced that the key parameter for the transition between these two tunneling regimes is the electron scattering. For these junctions a strong asymmetric behaviour in the I-V characteristics and the tunnel magnetoresistance (TMR) is predicted which can be controlled by an applied magnetic field. This phenomenon relates to the quantum well states in the middle metallic layer. The corresponding resonances in the current and the TMR are drastically phase-shifted under positive and negative voltage.