Investigation of magnetotransport properties in Ni/Pt and Co/Pd layered structures

Abstract

In this thesis two topics in the field of magnetotransport properties of thin ferromagnetic layered structure in current in-plane (CIP) geometry are studied. First the magnetoresistance effects in Ni/Pt system were investigated in the temperature range of 4.2 ≤ T ≤ 295 K. In Pt/Co/Pt the resistivity behaves as ρ(φ,θ) = ρ_t+ Δρ_ip cos² φ sin² θ + Δρ_op cos² θ where φ/θ is the angle between magnetization and current direction/film normal. While Δρ_ip is caused by the conventional AMR (bulk effect) a Δρ</sub>op</sub> ∝ 1/t behavior was found for Pt(5nm)/Co(t)/Pt(3nm) sandwiches revealing that Δρ_op originates at the Co/Pt interfaces (anisotropic interface magnetoresistance (AIMR)). In order to study interfacial MR contribution in stacking isoelectronic materials Ni/Pt systems were investigated. We prepared Pt(5nm)/Ni(t)/Pt(3nm) sandwiches with Ni thicknesses of 1 – 50nm by DC magnetron sputtering on Si₃N₄ substrate. As a result, in contrast to previous findings, the ρ(θ) behavior can only be satisfactorily described when considering higher orders in the expansion of the MR: ρ(θ)=ρ_t + ∑_n Δρ_(op,2n) cos²n θ with n ≤ 3. The thickness dependence of the amplitudes Δρ_(op,2n) behaves according to 1/t revealing that also the higher orders have their origin at the Ni/Pt interfaces. The second topic of this thesis deals with investigation of the impact of aging on the various magnetoresistance effects in Pd/Co/Pd sandwiches at room temperature. By means of sputtering techniques two Pd(5 nm)/Co/Pd(3 nm) samples with 2 and 7nm Co thicknesses were fabricated on Si₃N₄ substrate and the longitudinal and transverse resistivity of the sandwiches were measured repeatedly over 600 days. The results show strong variations of the MR properties in the first three months followed by a slower change to equilibrium values. However, there are significant differences between both samples reflecting different behavior of Co/Pd systems governed by bulk-like or interface contributions. In order to find a correlation between the changes occurring in MR effects and the structural properties of the samples, XRR measurements accompanied the transport investigations over time. It is concluded that gradual intermixing of Co and Pd at the interfaces and absorption of hydrogen are the two mechanisms responsible for the aging effect in Pd/Co/Pd systems.