Structure analysis and local magnetic parameters of magnetoresistance tunnel junctions

The Magnetic Tunnel Junctions (MTJs) were deposited by DC magnetron sputtering method in the following layer sequence: Ta(50 Å)/Cu(100 Å)/Ta(50 Å)/Ni₈₀Fe₂₀(20 Å)/Cu(50 Å)Mn₇₅Ir₂₅(100 Å) /Co₇₀Fe ₃₀(25 Å)/Al-O/Co₇₀Fe₃₀(25 Å)/Ni₈₀Fe₂₀(t)/Ta(50 Å)/, with t = 0 Å, 100 Å and 1000 Å. 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. An improvement of (111) texture and crystallinity was observed after annealing. The tunneling magnetoresistance ratio of patterned junction with electrode layer of Ni₈₀Fe₂₀ (t = 1000 Å) deposited on the free layer of Co₇₀Fe₃₀ (25 Å) exceeds 40% at a room temperature after annealing at 200°C in the magnetic field of 1 kOe. Local hysteresis loops were measured using the magneto-optical Kerr effect system. Relatively irregular variations of the coercive force H _c and unidirectional anisotropy field H_ua in as-deposited sample are revealed. After 200°C annealing, the H_c decreases but H_ua increases with smooth local variations. Two-dimensional plots of H_c and H_ua show symmetric saddle shapes with their axes aligned with the pinned layer. The distribution of surface roughness is symmetric with respect to the centre of MTJ. Correlation between surface roughness and the variation of H_ua suggests that the H_ua variation of the free layer is well described by dipole interactions in the form of so-called Néel "orange peel" coupling.