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1 2003

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Structure analysis and local magnetic parameters of magnetoresistance tunnel junctions

Kim C., Kim C. O., Hu Y., Kanak J., Stobiecki T., Ogata S., Tsunoda M., Takahashi M.

Materials Science

2003

Vol. 21, No. 1

9-23

The Magnetoresistance Tunnel Junctions (MTJ) were deposited by DC magnetron sputtering method in the following layer sequence: Ta(50A)/Cu(100A)/Ta(50A)/Ni80Fe20(20A)/Cu(50A)/Mn75Ir25(100A)/Co70Fe30(25A)/Al-O/Co70Fe30(25A)/Ni80Fe20(t) /Ta(50A)/, with t = 0A, 100A and 1000A. X-ray diffraction analysis revealed that highly oriented fcc-(111) of IrMn3, Cu, Ni80Fe20 and Co70Fe30 crystal planes are stacked parallel to the substrate plane. The improvement of (111) texture and crystallinity was observed after annealing. The tunneling magnetoresistance ratio of patterned junction with electrode layer of Ni80Fe20 (t = 1000A), deposited on the free layer of Co70Fe30 (25A) exceeds 40% at room temperature after annealing at 200°C in magnetic field 1kOe. The local hysteresis loops were measured using the magneto-optical Kerr effect system. The relatively irregular variations of coercive force Hc and unidirectional anisotropy field Hua in as-deposited sample are revealed. After 200°C annealing Hc decreases but Hua increases with smooth local variations. Two-dimensional plots of Hc and Hua show the symmetric saddle shapes with their axes aligned with the pinned layer. The distribution of surface roughness is symmetric with respect to the center of MTJ. Correlation between surface roughness and the variation of Hua suggests that the Hua variation of the free layer is well described by dipole interactions in the form of socalled Néel "orange peel" coupling.