Spin blockade effects in chromium oxide intergrain magnetoresistance

CrO ₂ thin films with crystallites of a significant size permit investigation of the thin intergrain conduction between a limited numbers of crystals. Phoemission techniques reveal that the CrO ₂ films are covered by a 1-2-nm-thick Cr ₂O ₃ insulating barrier. The electronic band gap of the surface electrons is 3.4 eV at low temperatures, decreases sharply down to 2.8 eV at ambient. Electric transport though a few junctions in series shows a remarkable zero-bias anomaly, interpreted in terms of blockade effects. We show that the magnetoresistance is governed by low-bias blockade in these junctions.