Abstract: A magnetic gradiometer can be used in systems or methods for nondestructive testing, even when the material being tested is weakly magnetic. The magnetic gradiometer can include a printed circuit board (PCB) comprising a first end and a second end separated by a base length; an excitation coil encircling at least a portion of the PCB and configured to deliver an alternating current (AC) to generate an excitation magnetic field; and a differential sensor. The differential sensor can include a reference magnetic tunneling junction in magnetic vortex state (vortex MTJ) sensor array at the first end to generate a voltage based on the excitation magnetic field; and a signal vortex MTJ sensor array at the second end to generate another voltage based on the excitation magnetic field due to a composition of the measurement target. The second end of the PCB can be oriented towards the measurement target.

Abstract: A magnetic tunneling junction sensor includes a free ferromagnetic layer of material, a pinned ferromagnetic layer of material, the free ferromagnetic layer and the pinned ferromagnetic layer separated by a thin insulating layer of material through which electrons can tunnel, an oxidized silicon wafer, the free ferromagnetic layer, thin insulating layer and the pinned ferromagnetic layer deposited on the oxidized silicon wafer, and extrinsic magnetic flux.

Abstract: A magnetic tunneling junction sensor includes a free ferromagnetic layer of material, a pinned ferromagnetic layer of material, the free ferromagnetic layer and the pinned ferromagnetic layer separated by a thin insulating layer of material through which electrons can tunnel, an oxidized silicon wafer, the free ferromagnetic layer, thin insulating layer and the pinned ferromagnetic layer deposited on the oxidized silicon wafer, and extrinsic magnetic flux