Proximity effect in MgB$_{2}$-Permalloy hybrid system*

Recently ferromagnet/superconductor systems have attracted a great attention due to their scientific interest and potential for the technological application. So far, most of the work has been done for Nb with ferromagnetic metals or high temperature oxide superconductors with magnetic oxides. In this presentation we will discuss the proximity effect in magnesium diboride (MgB$_{2})$/Py thin films, where the superconducting property changes due to the adjacent Py layer. Even though the good electronic properties such as large critical current density and large coherence length of MgB$_{2}$ make it a good candidate for superconducting electronic applications, depositing a good-quality \textit{in-situ} MgB$_{2}$ thin film is still challenging. Especially for the multilayer deposition, it is ideal to deposit all the layers \textit{in-situ} without \textit{ex-situ} treatment. We used a sputtering to deposit the MgB$_{2}$ layer \textit{in-situ} and made a hybrid system with Py. We found that the substrate temperature during the MgB$_{2}$ deposition is the most important parameter to determine the superconducting transition temperature of the sample. In addition to the proximity effect we will also discuss the problem with a sputtering method for MgB$_{2}$ deposition.