(100) Epitaxial and (111) Polycrystalline Spin Valve Heterostructures on si (100): Magnetotransport and the Importance of Interface Mixing in Ion Beam Sputtering

Abstract

We have investigated magnetoresistance properties of (100) epitaxial, (11) textured and polycrystalline spin valve heterostructures of the form Ni80Fe20/Cu/NiNi80Fe20/Fe50Mn50 on (100) Si substrates by ultra high vacuum (UHV) ion beam sputtering at room temperature. Magnetoresistance was measured as a function of Cu interlayer thickness (ti) with 10 Å ≤ti ≤ 100 Å and the maximum was found at 20 Å in the case of (100) epitaxial spin valves. Highly (11) textured spin valves with heterostructure configurations similar to the (100) spin valves were found to have a slightly lower magnetoresistance than the (100) heterostructures, but the functional dependence of the magnetoresistance on ti was very similar.Interface mixing during the sputtering process by energetic neutral bombardment was found to significantly affect the magnetoresistance. Samples were made under various sputtering conditions (gas pressure, ion beam energy, target and substrate configuration) that could enhance or suppress high energy neutral bombardment of the growing film surface. Samples made under the conditions that suppressed neutral bombardment showed higher magnetoresistance and more abrupt interfaces as confirmed by small angle X-ray diffraction analysis of interface mixing by energetic neutral bombardment during sputter deposition.