Low frequency picotesla field detection using hybrid MgO based tunnel sensors

  • Chaves R
  • Freitas P
  • Ocker B
 et al. 
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Abstract

Low frequency ultrasensitive magnetic sensors are required for magnetocardiography (1 pT at 10 Hz) applications. MgO based magnetic tunnel junctions with RA = 100–150 Ω μm2 and tunnel magnetic resistance = 100% were patterned into rectangular pillars with side up to 50 μm. Sensors were incorporated in 500 nm thick Co94Zr3Nb4 flux guides. Sensor linearization was achieved through internal (Co66Cr16Pt18 pads) and external (3.5 mT) longitudinal bias fields resulting in sensitivities of 720%/mT. Noise levels of 97 pT/Hz0.5 at 10 Hz, 51 pT/Hz0.5 at 30 Hz, and 2 pT/Hz0.5 at 500 kHz were measured in the linear region of the transfer curve. © 2007 American Institute of Physics

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Authors

  • R. C. Chaves

  • P. P. Freitas

  • B. Ocker

  • W. Maass

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