Journal
APPLIED PHYSICS LETTERS
Volume 93, Issue 19, Pages -Publisher
AMER INST PHYSICS
DOI: 10.1063/1.3021372
Keywords
boron alloys; cobalt alloys; giant magnetoresistance; grain boundaries; grain growth; grain size; heat treatment; iron alloys; magnesium compounds; magnetic thin films; magnetic tunnelling; transmission electron microscopy; tunnelling magnetoresistance
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In order to promote the grain growth of ultrathin MgO barrier deposited on a CoFeB layer, in situ infrared (IR) heat treatment just after the deposition of MgO barrier was examined. In case that IR heat treatment was not applied, tunneling magnetoresistance (TMR) ratio of CoFeB/MgO/CoFeB magnetic tunnel junction (MTJ) was significantly decreased with decreasing resistance area (RA) product to less than 10 Omega mu m(2). On the other hand, TMR ratio of 206% was achieved at the RA product of 2.1 Omega mu m(2) when the IR heat treatment was applied. According to the cross sectional transmission electron microscope images for the samples with 0.76-nm-thick (similar to 4 ML) MgO barrier, the (001) oriented well crystallized structure with smooth interface was observed for the IR heated sample. Moreover, it revealed that the lateral grain size of MgO was significantly enlarged compared to that for the sample without IR heating. The improvement of TMR properties at low RA product region by the heat treatment might be due to the decrease in grain boundaries of MgO layer where the coherent tunneling of Delta(1) electrons is not restricted.
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