Magnetic Properties And Transport Properties Of YBa₂Cu₃O_7-x/CoFeMnSi Thin Films

Superconducting materials have been closely related to magnetism since their discovery,and the spin mechanisms between them compete with each other.Therefore,the interaction between superconductors and ferromagnets has always been a major research direction for scientists.There are unique physical mechanisms such as proximity effect,LOFF state,Andreev scattering,and spin-triplet Cooper pairs when superconductors and ferromagnets are in contact.With the development of condensed matter physics,some new spin mechanisms of superconductors and ferromagnets have been discovered separately.However,since the discovery of superconductors was relatively late,most researchers focused on changes in superconducting performance when studying the interaction between superconductors and ferromagnets.Continuing to study the interaction between superconductors and ferromagnets is conducive to preparing materials that can be applied in environments requiring complex magnetic or electrical transport properties.In this paper,the second-class high-temperature superconductor YBa₂Cu₃O_7-x and the spin-gapless semiconductor CoFeMnSi were selected as research objects,and we mainly studied the magnetic and electrical transport properties of the system when they are in contact.The main work of this paper is as follows:1.CoFeMnSi thin films with in-plane magnetic anisotropy（IMA）were grown on YBa₂Cu₃O_7-x,and partial diamagnetism was observed at low temperatures in multi-layered films.The magnetic contribution of the superconducting layer at low temperatures was much greater than that of the ferromagnetic layer.By changing the thickness of the CoFeMnSi layer,it was confirmed that there are proximity effects and spin-triplet Cooper pair correlations between the superconducting and ferromagnetic layers that affect the magnetic properties of the multi-layered film.Changing the thickness of the ferromagnetic layer can affect the possibility of these effects,thus regulating the magnetic properties of the multi-layered film and causing in-plane and out-of-plane performance anisotropy.Later,by inserting MgO and Pt between CoFeMnSi and YBa₂Cu₃O_7-x respectively,it was confirmed that the occurrence of reverse proximity effects must be completed by electron and electron pair migration.They can cross the Pt layer but will be suppressed by MgO,which will enhance the occurrence of reverse proximity effects due to the insertion of Pt.The study of thin film section morphology confirmed that heterogeneous interfaces can indeed affect the occurrence of spin-triplet Cooper pairs.The study of the anomalous Nernst effect showed that the insertion of YBa₂Cu₃O_7-x can produce shunting,reducing the anomalous Nernst voltage of the multi-layered film.2.CoFeMnSi cyclic structures with perpendicular magnetic anisotropy（PMA）were grown on YBa₂Cu₃O_7-x using Pt or MgO as intermediate layers.It was confirmed that the low-temperature magnetic contribution of the superconducting layer is suppressed regardless of whether Pt or MgO is used as the ferromagnetic and superconducting intermediate layer.When Pt is used as the intermediate layer,the isotropic YBa₂Cu₃O_7-x insertion leads to the originally PMA film being isotropic at room temperature,and PMA weakens at low temperatures.However,when MgO is used as the intermediate layer and YBa₂Cu₃O_7-x is inserted,the film becomes isotropic at room temperature,but its low temperature PMA performance improves by an order of magnitude.By analyzing the thin film section morphology and element composition,this study concluded that the main source of PMA performance of the thin film is the hybridization of Co and Fe elements diffusing into the Pt layer and the spin-orbit coupling effect brought by Co-O and Fe-O bond formation with O.The measurement results of the anomalous Hall effect showed that when there are Pt or MgO intermediate layers,normal ferromagnetic Hall backlines can be measured at high temperatures in the multi-layered films.When the temperature is lowered to the point where YBa₂Cu₃O_7-x begins to undergo superconducting transition,YBa₂Cu₃O_7-x contributes to the Hall effect and the Hall backline changes abnormally.As the temperature continues to decrease,YBa₂Cu₃O_7-x no longer contributes to the Hall effect,but the overall Hall resistance becomes extremely small due to the shunting of the superconducting layer.