Exchange biasing of permalloy films by Mn_xPt_1-x: Role of composition and microstructure

Abstract

The interfacial coupling energy, Δσ for polycrystalline Ni 0.8Fe0.2 (100 Å)/MnxPt1-x. (t Å)/SiO2 bilayers, has been determined from wedge samples spanning a MnxPt1-x composition range 0.42 <x<0.76 and t∼350 Å. Δσ 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 xPt1-x: [Ni0.85Fe0.15(100 Å)/Mn0.49Pt0.51(t Å)]. In one case (normal structure), the epitaxial permalloy was grown first onto Pt/MgO(001), followed by 170 Å of Mn0.49Pt0.51. In the other structure (inverted), a 350 Å thick polycrystalline film of Mn0.49Pt 0.51 was grown onto a SiO2 substrate, followed by permalloy. The structures exhibited very different exchange bias fields (32 versus 86 Oe) and Δσ values (0.021 versus 0.060 erg/cm2), respectively. Significant differences in texture, grain size, and Mn 0.49Pt0.51 layer thickness for the two samples are reported. © 1998 American Institute of Physics.