IMPROVED EXCHANGE COUPLING BETWEEN FERROMAGNETIC NI-FE AND ANTIFERROMAGNETIC NI-MN-BASED FILMS

Dc magnetron sputtered Ni-Mn and Ni-Mn-Cr films are demonstrated to ex hibit strong and thermally stable antiferromagnetism, as well as high corrosion resistance. For a 25.2 nm thick 53.3 Ni-46.7 Mn (in atomic p ercent) film deposited on top of a 28.5 nm thick 81 Ni-19 Fe film, a u nidirectional anisotropy field (H(UA)) of 120.6 Oe is obtained at room temperature after annealing in vacuum. The equivalent interfacial exc hange coupling energy (J(K)) is 0.27 erg/cm, three times higher than t hat of bilayer Ni-Fe/50Fe-50Mn films. This strong exchange coupling ap pears correlated with the presence of an antiferromagnetic theta (NiMn ) phase with a CuAu-I-type ordered face-centered-tetragonal structure. The blocking temperature, at which the exchange coupling disappears, is higher than 400-degrees-C. The Cr addition to the Ni-Mn film dilute s the exchange coupling, but the J(K) for the Cr content less-than-or- equal-to 10.7 at. %, is still higher than that of the Ni-Fe/Fe-Mn film s. Both Ni-Mn and Ni-Mn-Cr films exhibit corrosion behaviors much bett er than the Fe-Mn film and comparable to the Ni-Fe film. The films are proposed as longitudinal bias layers for the stabilization of magneto resistive read sensors.