| Research Abstract |
For application of spin valve elements to a new electromechanical transducer, basic investigations were carried out and the following results were obtained.
1. Large exchange interaciton fields. H_<ex> were obtained in MnPt/FeCo bilayrs.
i) In Cu/FeCo/MnPt films, the maximum H_<ex> appears for the MnPt film with Mn content of 51 at% after annealing. In this case, the resistivity and the blocking temperature of the Mn_<51>Pt_<49> films are about 255 muOMEGA cm and 300 - 370ﾟC,repectively.
ii) On annealing of FeCo/MnPt bilayrs, the CuAu-I type fct ordered MnPt crystals grow, causing the increase in H_<ex> above 230ﾟC and then reaching the maximum of 286 - 356 Oe at 320ﾟC.Above 350ﾟC,the value of H_<ex> decreases because of inter-diffusion at the layr boundaries, which was confirmed by RBS.In order to prevent the inter-diffusion, we deposited a thin Ag layr between FeCo and MnPt layrs, which brought an improvement in the thermal stability.
2. Spin valve films having high field-sensitivity and good thermal stability were obtained.
i) Thermal stability of FeCo (50*) /Cu(t_<Cu>) /FeCo (35*) /MnPt (300*) films : The film of t_<Cu> = 30* shows the maximum magnetoresistance (MR) ratio, 6.2%, after annealing at 290ﾟC.However, the value of MR ratio decreases during annealing for long time. On the other hand, the films of t_<Cu> >= 40* are stable up to 320ﾟC.
ii) Enhancement of the field sensitivity : Soft magnetic granular Fe-SiO_2 layr was deposited on the FeCo fre layr and the field sensitivity was increased.
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