Preparation And Electronic Transport Properties Of Layered Strontium Ruthenate Epitaxial Thin Films

The layered strontium ruthenate compounds(Sr_n+1Ru_nO_3n+1,n=1,2,…,∞)are typical transition metal oxides with a Ruddlesden-Popper（R-P）structure.Their physical properties are drastically affected by the number of interleaving perovskite blocks（n）between rock-salt Sr-O layers.For n=1,the layered Sr₂Ru O₄ is an unconventional superconductor with triple pairing of spins.For n=2,the double-layered Sr₃Ru₂O₇ exhibits a metamagnetic transition（MMT）from a low magnetized state to a ferromagnetic state when exposed to a high in-plane magnetic field（～5 T parallel to the plane containing the Ru O₆ octahedron）.Near the MMT,the maximum magnetoresistance can be clearly observed.Interestingly,the end-member perovskite Sr Ru O₃（n=∞）is an electrocatalytic material with good oxygen evolution reaction activity and stability.Due to their unique electronic structures and novel functionalities,the layered strontium ruthenate compounds have garnered significant experimental and theoretical attention.As an important member of the strontium ruthenate family,Sr₃Ru₂O₇ has garnered significant attention from researchers due to its diverse range of physical properties.Under an external magnetic field,variable magnetic transition,spin density wave,and reluctance peak can be induced.However,the growth of Sr₃Ru₂O₇ film on a single crystal substrate is challenging and requires a growth temperature of 1100℃.As a result,most of the relevant research on Sr₃Ru₂O₇ is based on single crystal blocks,and there are few reports on thin film research in this field.Therefore,the properties of Sr₃Ru₂O₇ films grown on stressed substrates remain unclear.In this paper,the growth process of Sr₃Ru₂O₇ films was optimized using pulsed laser deposition.For the first time,Sr₃Ru₂O₇ epitaxial films were successfully prepared on（La Al O₃）_0.3（Sr₂Al Ta O₆）_0.7（LSAT）and Sr Ti O₃（STO）single crystal substrates at a low temperature of 680℃.Furthermore,the electrical properties of Sr₃Ru₂O₇ films with stress on the substrate were systematically studied.The main outcomes of this study are as follows:（1）The study found that by regulating the oxygen partial pressure during film growth,the phase structure of Sr₃Ru₂O₇ epitaxial films can change from Sr Ru O₃ to Sr₃Ru₂O₇.A transition oxygen partial pressure area near 30 m Torr was identified.The electrical and magnetic properties of films grown at different oxygen partial pressures were also verified.（2）This study investigated the electric transport and magnetic properties of Sr₃Ru₂O₇ epitaxial films grown on STO（001）single crystal substrates for the first time.The physical properties of the films were found to be affected by the stress of the substrate on the film.The film showed a large anisotropy in electrical performance when its reluctance was below 15 K,and the reluctance peak moved towards a lower intensity magnetic field than the reluctance peak in the block.The M-T curve behavior and hysteresis loop were also found to be different from those in the block,with ferromagnetic transition points and antiferromagnetic sequences at different temperatures.（3）Finally,the effect of film thickness size on the physical properties of Sr₃Ru₂O₇films on LSAT single crystal substrates was studied.The reluctance peaks of films with different thicknesses were not affected,and all appeared at 8.5 T.The reluctance behavior was similar to that of STO substrates,showing negative long-range reluctance behavior at 110 K and positive reluctance behavior at 15 K as the temperature decreases further.