Proper and improper SrRuO3 phase and corresponding itinerant ferromagnetic behavior

Summary form only given. SrRuO₃ is a very important member of layered Ruddlesden-Popper series of Sr_n+1Ru_nO_3n+1 compounds; where n (= 1, 2, 3 and ∞) indicates number of RuO₆ octahedral layers per formula unit. Structural, transport and magnetic properties in Ruddlesden-Popper series vary with different values of `n´. For example; Sr₂RuO₄ (n=1) is a possible p-wave spin-triplet superconductor [1], Sr₃Ru₂O7 (n=2) is a bilayered paramagnetic metal with quantum criticality [2], Sr₄Ru₃O₁₀ (n=3) is a structurally distorted ferromagnetic (or metamagnetic) metal [3] and SrRuO₃ (n=∞) is a perovskite structured ferromagnetic metal [4,5]. Due to its itinerant ferromagnetic behavior and ability of easy epitaxial growth on many perovskite substrates, SrRuO₃ is vastly used as a conducting electrode in multilayer device applications, magnetic tunnel junctions, electronic transport tuning, dynamic random access memory applications, switchable acoustic wave resonators, spintronic devices and many more.³¹-³⁸ The SrRuO₃ single crystals show long range ferromagnetic ordering at 165 K (T_C, Curie temperature) and low temperature ferromagnetic moment of ~1.6 μB/Ru [6-10]. But, achieving these values experimentally for polycrystalline SrRuO₃ is not easy due to many reasons such as volatile nature of RuO₂. It has been reported earlier that Ru vacancies created due to the deficiency of Ru is responsible for getting reduced T_C and magnetic moment. In our experiment, it has been observed that Ru deficiency is leading to the formation of the secondary Sr₃Ru₂O₇ phase in the system. We observed that the secondary phase is increasing with extended annealing. The evolution of the secondary phase of Sr₃R- ₂O₇ is accompanied with the change of the magnetic moment and resistivity of the system. For a particular processing condition, a single phase SrRuO₃ phase is observed and it´s Curie temperature (T_C) as high as 164 K and low temperature ordered magnetic moment ~1.6 μ_B/Ru has been achieved, which is almost equal to the values shown by SrRuO₃ single crystal. Additionally, the metal-metal transition and resistivity has been observed to be affected with the presence of Sr₃Ru₂O₇ phase and shows lowest resistivity for the system which exhibits best magnetic response. This correlation in ferromagnetism and resistivity is an indirect evidence that ferromagnetism of SrRuO₃ is due to the itineration of electrons. Moreover, a crossover from Fermi liquid (FL) to non-Fermi liquid (NFL) like behavior have been observed for all systems near 40-50 K.