Improving magnetic field detection limits of spin valve sensors using magnetic flux guide concentrators

The magnetic field detection limit of spin valve sensors in the thermal noise regime is improved from 1.3 nT/HZ(1/2) to 0.064 nT/Hz(1/2) by incorporating a Co93Zr3Nb4 soft magnetic flux guide concentrator structure. Linear spin valve sensors were processed down to 20 x 2 mu m(2) dimensions, with and without an additional 3500-angstrom-thick flux guide concentrator, with a magnetic flux gain factor ranging from 5 to 20. Spin valves show a starting sensitivity of 0.2 %/Oe, improved to 3.8 %/Oe with the flux concentrator. Noise measurements from dc to 500 kHz were performed, indicating similar noise levels with and without flux concentrators. In terms of magnetic field detection, sensors with flux concentrators show a detection limit of 2 nT/Hz(1/2) at 10 Hz, compared to 47 nT/Hz(1/2) without flux concentrators. No additional 1/f noise is measured in the spin valve sensor response upon the addition of the soft magnetic flux concentrators in the frequency range studied.