Exchange Biasing of Permalloy Films by MnxPt1–x: Role of Composition and Microstructure

The interfacial coupling energy, Δ σ for polycrystalline Ni0.8Fe0.2 (100 Å)/Mn x Pt1– x ( t Å)/SiO2 bilayers, has been determined from wedge samples spanning a Mn x Pt 1– x composition range 0.42 < x < 0.76 and t ~ 350 Å. Δ σ exhibits a sharp peak of 0.1 erg/cm 2 at 51% Mn. We compare the magnetic and microstructural properties of two bilayer films, which have the same compositions of permalloy and Mn x Pt 1– x : [Ni 0.85 Fe 015 (100 Å)/ Mn 0.49 Pt 0.51 ( t Å)]. In one case (normal structure), the epitaxial permalloy was grown first onto Pt/MgO(001), followed by 170 Å of Mn 0.49 Pt 0.51 . In the other structure (inverted), a 350 Å thick polycrystalline film of Mn 0.49 Pt 0.51 was grown onto a SiO 2 substrate, followed by permalloy. The structures exhibited very different exchange bias fields (32 versus 86 Oe) and Δ σ values (0.021 versus 0.060 erg/cm 2 ), respectively. Significant differences in texture, grain size, and Mn 0.49 Pt 0.51 layer thickness for the two samples are reported.