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In this article, we report the magnetic properties of ultrathin (15–200 Å) NiFe and CoFe films deposited using ion beam deposition techniques. They are symmetrically sandwiched between Ta, Cu, or Ta/Cu under and capping layers. NiFe and CoFe films grown between Ta/Cu and Cu/Ta bilayers exhibit the smallest magnetic thickness loss of about 1 Å. This interfacial magnetic dead layer thickness, t0, is about 5 Å for Cu-sandwiched films and about 15 Å for Ta-sandwiched films. As the film thickness becomes thinner than 100 Å, the magnetic properties are found to be more sensitive to the choice of material and growth environment. CoFe films show an interfacial contribution, λi, about ten times larger than that for NiFe films. Among others, NiFe and CoFe films sandwiched by Ta/Cu and Cu/Ta bilayers exhibit the smallest values of λi. The magnetic anisotropy in Ta-sandwiched CoFe films appears to be predominantly magnetoelastic in nature.

Spin-valve ͑SV͒ films Si͑100͒/Ta30/NiFe50/CoFe20/Cu26/CoFe23/Ru7/CoFe20/IrMn50/Ta30 ͑in Å͒ exhibit a room temperature ͑RT͒ giant magnetoresitance ͑GMR͒ ratio of 8.5% with an effective exchange pinning field (H eex ) of ϳ1.3 kOe and an antiferromagnetic ͑AF͒ saturation field ͑Hs͒ of ϳ6.0 kOe. The synthetic spin valve shows a GMR ratio of 5.0% at 150°C with H eex Ͼ500 Oe, while a conventional spin valve ͓Si͑100͒/Ta50/NiFe50/CoFe20/Cu28/CoFe22/IrMn50/Ta50 in Å͔ has a GMR ratio of 5.0% with H ex Ͻ200 Oe. The synthetic sample also showed a superior thermal stability with a RT GMR value of 6.9% ͑compared to 6.1% for conventional sample͒ after an anneal at 250°C for 10 h. Shielded narrow track synthetic SV readers demonstrated high amplitude, large dynamic range, and excellent magnetic stability, indicating extendibility for ultrahigh density read head applications.

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Magnetic field-induced martensitic transformations in disordered and ordered Fe-24 at%Pt alloys were studied to examine the effect of degree of order (S) on the transformations by measuring the m agnetization and electrical resistivity, applying a pulsed ultra-high magnetic field. As a result, it is found that a magnetic field higher than a critical strength is needed to induce the martensitic transformations at temperatures above M without regard to the degree of order. The critical strength increases with a straight line for the non-thermoelastic alloys with S<0.5, but on a curved line for the thermoelastic ordered alloys with S=0.7-0.8, as if the curve diverges near the respective To temperature. The divergence phenomenon seems to suggest that the To temperature is a maximum one above which martensites can not be induced even though any high magnetic field is applied. The amount of magnetic field-inlarger the amount of martensites becomes. A thermodynamic calculation for the increase of Ms temperature suggests that the effect of a magnetic field on martensitic transformations may result in not only the Zeeman effect but also another unknown effect.