Correlation between structure and exchange coupling parameters of IrMn based MTJ

Magnetic tunnel junctions (MTJ's) with the structure sub/Ta(5)/Cu(10)/Ta(5) /NiFe(2)/Cu(5)/IrMn(10)/CoFe(2.5)/Al-O/CoFe(2.5)/NiFe(t)/Ta(5), where t = 10, 30, 60 and 100 nm in as-deposited and annealed state were characterized by XRD and magnetic hysteresis loop measurements. The XRD measurements were done in grazing incidence (GID) scan-2θ and θ-2θ geometry, by rocking curve (ω-scan) and pole figures in order to establish the correlation between microstructure (texture and crystallites size) and magnetic parameters of exchange bias and interlayer coupling. Annealing in vacuum at 300°C led to an increase of the average crystallite size of Ir₂₅Mn₇₅ and Ni₈₀Fe₂₀ and improvement of the (111) plane texture of Ir₂₅Mn₇₅, Cu and Ni₈₀Fe₂₀. The exchange bias fields and the coercivity of the pinned layer linearly increased with increasing grain size of IrMn. A reciprocal proportionality between interlayer coupling field and coercivity of the free layer and grain size of NiFe was found. The enhancement of interlayer coupling between pinned and free layers, after annealing treatment, indicates the correlated in-phase roughness of dipolar interacting interfaces due to increase of the crystallite size of NiFe.