Normal and inverse bulk spin valve effects in single-crystal ruthenates

摘要

The current-perpendicular-to-plane magnetoresistivity (CPP-MR)/ρ_c(B) is investigated in single crystal ruthenates Ca_3(Ru_(1-X)Ti_x)_2O_7 (x = 0.02). This material is naturally composed of ferromagnetic metallic bilayers (Ru,Ti)O_2 separated by nonmagnetic insulating layers of Ca_2O_2, resulting in tunneling magnetoresistivity. Non-monotonic ρ_c(B) curves as well as the inverse spin valve effect are observed around the magnetic phase transition associating with the metal-to-insulator transition. A spin dependent tunneling model with alternate distribution of hard and soft magnetic layers [(Ru,Ti)O_2] is proposed to explain the exotic CPP-MR behavior. This eccentric CPP-MR behavior highlights the strong spin-charge coupling in double-layered ruthenates and provides a potential material for spintronic devices.