Spin filtering and an enhanced regime of giant magnetoresistance

A new regime of magnetoresistance (MR) in systems composed of magnetic laye rs separated by non-magnetic modulated structures is studied. The ability t o tailor the electronic structure of superlatticed systems enables one to e ngineer contrasting spin-dependent transport properties, enhancing the magn etoresistance ratios. When the system acts as a spin filter the MR ratios r each values many orders of magnitude larger than those of conventional gian t magnetoresistance. Rather than a mere enhancement of the magnetoresistanc e ratios, this new regime involves ingenious combinations of spin-polarized currents. Moreover, it results from a magnetic-field-induced metal-insulat or transition along the modulation direction, characterizing a highly aniso tropic transport behaviour. The existence of an insulating phase circumvent s the experimental challenge of probing excessively small resistances in th e current-perpendicular-to-plane (CPP) geometry of magnetoresistance. A pic ture in terms of the hulk Fermi surfaces of the constituent materials emerg es and provides general guidelines on how to achieve this regime.