Inverse Square Sensitivity Noise Spectroscopy of Spin-based and Semiconductor-Based Magnetoresistive Systems Edmund R. Nowak, Department of Physics & Astronomy, University of Delaware The most likely technology for advancing small, low power magnetic sensors is based on magnetic tunnel junctions (MTJs). MTJs are devices that utilize the spin of the electron, in addition to its charge, to achieve very large changes in resistance (greater than 400% at room temperature) in response to small magnetic fields. Based on our experimental studies of noise in these devices, we have developed a theoretical model (below) and incorporated it into a spreadsheet for easy evaluation of the expected performance of sensors. Our current effort is directed at understanding the underlying mechanisms responsible for magnetic 1/f noise, the last term below, which is expected to set the ultimate sensitivity of practical sensors based on MTJs. Noise Power (Detection Limit) (T/Hz½)2 Amplifier Noise Johnson and Shot Noise Electronic 1/f Noise Thermal Magnetic White Noise Inverse Square Sensitivity Magnetic 1/f noise Material Parameters αelec : Electronic 1/f noise strength αmag : Magnetic 1/f noise strength f : Detection frequency αG : Damping parameter Ω : Free layer volume γ : Gyromagnetic ratio [RAP] : Resistance Area Product Bsat : Saturation field (T) ΔR/R : Fractional resistance change MS : Free layer intrinsic magnetization Recent advances in tunneling magnetoresistance, free-layer saturation field, and MEMS oscillating flux concentrators suggest that it may be possible to extend small, inexpensive, low-power, ultra-sensitive magnetic sensors, which is currently dominated by fluxgates, optically pumped magnetometers and SQUIDS for low frequency applications. Wheatstone bridge N MTJ’s Device Architecture N shielded MTJ’s Device Parameters N : # of Sensing Junctions VJ : Junction Voltage R : Junction Resistance A : Junction Area