Tunneling magnetoresistance was found to be suppressed with decreasing temperature for magnetic tunnel junctions (MTJs) oxidized under high plasma power. A strong temperature dependence of the junction resistance was observed, along with zero-bias anomalies of dynamic resistance at low temperatures. Resistance shows a logarithmic dependence on temperature, and resistance versus temperature exhibits a scaling behavior. Our experimental data can be explained in a consistent way by the Kondo effect in the MTJs with the Kondo temperature TK=20-30 K.

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The ferromagnetic ordering in Mn-doped ZnO thin films grown by pulsed laser deposition (PLD) as a function of oxygen pressure and substrate temperature has been investigated. Room-temperature ferromagnetic behaviors in the Mn-doped ZnO films grown at 700°C and 800°C under 10 ÿ1 torr in oxygen pressure were found, whereas ferromagnetic ordering in the films grown under 10 ÿ3 torr disappeared at 300 K. The large positive magnetoresistance (MR), ;10%, was observed at 5 K at low fields and small negative MR was observed at high fields, irrespective of oxygen pressure. In particular, anomalous Hall effect (AHE) in the Mn-doped ZnO film grown at 700°C under 10 ÿ1 Torr has been observed up to 210 K. In this work, the observed AHE is believed to be further direct evidence demonstrating that the Mn-doped ZnO thin films are ferromagnetic.