1/f noise in linearized low resistance MgO magnetic tunnel junctions

Low RA MgO magnetic tunnel junctions prepared at Singulus (Ta 3/CuN 30/Ta 5/PtMn 20/CoFe 2.5/Ru 0.7/CoFeB 3/MgO 1.2/CoFeB 3/Ta 5 (thickness in nanometers) were microfabricated at INESC-MN. The junctions were patterned into micron-sized sensors (5-20 mu m(2)) with controlled shape anisotropy (aspect ratio ranging from 2 to 20). A small external longitudinal bias field (15-30 Oe) was further used to improve sensor linearity. The MgO junctions have a resistance-area product of 150 Omega mu m(2) and a maximum tunnel magnetoresistance of 130%. Noise measurements were done in linearized sensors, from dc to 500 kHz. The magnetic and nonmagnetic contributions to the 1/f noise were determined. From the data fitting, Hooge parameters of similar to 2.20x10(-9) mu m(2) were obtained for the nonmagnetic 1/f noise. Analysis of direct experimental data revealed the possibility to detect variations of magnetic fields in the order of 10(-10) T/Hz(0.5) with these MgO junctions, demonstrating their potential for ultralow-field detection. (C) 2006 American Institute of Physics.