Antiferromagnetically coupled CoFeB∕Ru∕CoFeB trilayers

This work reports on the magnetic interlayer coupling between two amorphous CoFeB layers, separated by a thin Ru spacer. We observe an antiferromagnetic coupling which oscillates as a function of the Ru thickness x, with the second antiferromagnetic maximum found for x=1.0–1.1nm. We have studied the switching of a CoFeB∕Ru∕CoFeB trilayer for a Ru thickness of 1.1nm and found that the coercivity depends on the net magnetic moment, i.e., the thickness difference of the two CoFeB layers. The antiferromagnetic coupling is almost independent of the annealing temperatures up to 300°C while an annealing at 350°C reduces the coupling and increases the coercivity, indicating the onset of crystallization. Used as a soft electrode in a magnetic tunnel junction, a high tunneling magnetoresistance of about 50%, a well-defined plateau and a rectangular switching behavior is achieved.