Bias-voltage dependence of magnetoresistance in magnetic tunnel junctions grown on Al2O3 (0001) substrates

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Abstract
Magnetic tunnel junctions with the structure of Al 2 O 3 (0001)/Pt (111) 20 nm/ Ni 80 Fe 20 (111) 50 nm/Al 1.6 nm–O/ Co 75 Fe 25 4 nm/ Ir 22 Mn 78 10 nm/ Ni 80 Fe 20 30 nm were fabricated using UHV sputtering and photolithography process. As the annealingtemperature increased up to 250 °C, tunnel magnetoresistance (TMR) ratio at 1 mV bias increased from 28% to 43% for t ox = 180 s plasmaoxidation and the V ± 1 ∕ 2 , at which the zero bias TMR value is halved, is +640 mV and−650 mV for positive and negative bias voltages, respectively. The bias-voltage dependence of TMR could be explained in terms of the relationship with V ± 1 ∕ 2 and the interface of the ferromagneticelectrode and the Al–O insulating layer. V + 1 ∕ 2 , which reflects the bottom ferromagnetic electrode-barrier interface state, changes with plasmaoxidation time, while V − 1 ∕ 2 , which corresponds to top ferromagnetic electrode-barrier interface, hardly changes.