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The magnetotransport properties of magnetic tunnel junctions (MTJ) fabricated with very high concentration ozone exposure were compared with those of plasma oxidized ones in order to study the ozone oxidation process of metal Al films. MTJs with structure of substrate/Ta/Cu/Ta/Ni76Fe24/Cu/Mn75Ir25/Co71Fe29/AlO/Co 71Fe29/Ni76Fe24/Ta were prepared on thermally oxidized Si wafers. All the metallic films were deposited by dc magnetron sputtering method. The barrier formation was performed by depositing a metal Al film and subsequently oxidizing it in the chamber with plasma or ozone oxidation method. A photolithographic process and ion milling were used to pattern the tunnel junctions. The tunneling magnetoresistance (TMR) measurements were performed with a four-point probe method at a bias voltage of 5 mV.