Bias-voltage dependence of magnetoresistance in magnetic tunnel junctions grown on Al2O3 (0001) substrates -: art. no. 102506

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 degrees C, tunnel magnetoresistance (TMR) ratio at 1 mV bias increased from 28% to 43% for t(ox)= 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. (c) 2005 American Institute of Physics.