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Tunnel magnetoresistance junctions with the structure of SrTiO3-sub/La-0.7 Sr-0.3 MnO3 (100nm)/La-0.96 Sr-0.04 MnO3 (5nm)/ La0.7Sr0.3MnO3 (100nm)/Ir-22 Mn-78 (15nm)/Ni-79 Fe-21 (5nm)/Pt (20nm) were micro-fabricated with lithography and Ar ion etching. The first three epitaxial layers of La0.7Sr0.3 MnO3 (100nm)/La-0.96 Sr-0.(04) MnO3 (5nm)/La-0.7 Sr-0.3 MnO3 (100nm) were deposited on single crystal (001) SrTiO3-substrate by magnetron sputtering and heat treatment, then the spinning and top conducting layers of Ir22Mn78(15nm)/Ni79Fe21(5nm)/Pt(20nm) were continuously fabricated on top the three epitaxial layers by normal magnetron sputtering. The colossal TMR ratio of 3270% was observed at 4.2K under the external magnetic field of 8 T. The polarization value of 97% for the La0.7Sr0.3MnO3 is well consistent with the theoretical value of 100% The present results directly indicate the half-metallic ferromagnetism in La0.7Sr0.3MnO3. Tire high TMR value can possibly be attributed to the good interface due to the perfect barrier.
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