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

Ahn, Sung-Jin; Kato, Takeharu; Kubota, Hitoshi; Ando, Yasuo; Miyazaki, Terunobu
March 2005
Applied Physics Letters;3/7/2005, Vol. 86 Issue 10, p102506
Academic Journal
Magnetic tunnel junctions with the structure of Al2O3 (0001)/Pt (111) 20 nm/Ni80Fe20 (111) 50 nm/Al 1.6 nm–O/Co75Fe25 4 nm/Ir22Mn78 10 nm/Ni80Fe20 30 nm were fabricated using UHV sputtering and photolithography process. As the annealing temperature increased up to 250 °C, tunnel magnetoresistance (TMR) ratio at 1 mV bias increased from 28% to 43% for tox=180 s plasma oxidation 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 ferromagnetic electrode and the Al–O insulating layer. V+1/2, which reflects the bottom ferromagnetic electrode-barrier interface state, changes with plasma oxidation time, while V-1/2, which corresponds to top ferromagnetic electrode-barrier interface, hardly changes.


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