Exchange-coupled Ni-Fe/Fe-Mn, Ni-Fe/Ni-Mn and NiO/Ni-Fe films for stabilization of magnetoresistive sensors

We have studied the unidirectional anisotropy field (H_UA) and coercivity (H_CE) in exchange-coupled Ni-Fe/Fe-Mn, Ni-Fe/Ni-Mn and NiO/Ni-Fe films as functions of thickness and temperature, and evaluated these films for the stabilization of magnetoresistive (MR) sensors. The as-deposited Ni-Fe/Fe-Mn and NiO/Ni-Fe films exhibit strong exchange coupling, while the Ni-Fe/Ni-Mn films require annealing to enhance exchange coupling. Both H_UA and H_CE follow an inverse dependence of the Ni-Fe film thickness in all cases, as expected from the interface nature of exchange coupling. The Fe-Mn film thickness required for the onset of exchange coupling is much smaller than the Ni-Mn and NiO film thicknesses. The thermal stability of the Ni-Fe/Ni-Mn films is superior to that of the Ni-Fe/Fe-Mn and NiO/Ni-Fe films. To explain annealing effects on exchange coupling in the Ni-Fe/Ni-Mn films, we propose an exchange-coupling model consistent with models applied to the Ni-Fe/Fe-Mn and NiO/Ni-Fe films in previous studies. Uniform-field tests of the MR sensors longitudinally biased by the three types of exchange-coupled films show quiet and stable MR responses in all cases. We evaluate the exchange-coupled films based on desired properties for the sensor stabilization, and then discuss their merits and deficiencies