Coupling Strength With Off-Axial External Field In Magnetic Tunnel Junction Cells

A series of hysteresis loops with off-axial external magnetic fields have been measured to identify magnetization reversal properties as well as coupling effects in magnetic tunnel junctions (MTJs). MTJ films, consisting of a synthetic artificial antiferromagnetic pinned layer of CoFeB/Ru/CoFe/IrMn, were patterned into an elliptical cell array with sizes of 200 x 300 nm and 500 x 750 nm. The hysteresis loops were measured using a vibrating sample magnetometer with various directions of the external magnetic field; the angle theta between the external magnetic field ((E) over right arrow (E)) and the biasing field of the pinned layer ((E) over right arrow (B)) was varied from 0 degrees to 90 degrees. The two significant coupling effects, ascribed to exchange bias between CoFe/IrMn and Ruderman-Kittel-Kasuya-Yosida-like coupling in CoFeB/Ru/CoFe, can be observed in these hysteresis loops. The angular dependence of the hysteresis loops is employed to characterize the variation of these coupling effects in extended and patterned MTJ films. (C) 2011 American Institute of Physics. [doi:10.1063/1.3560047]