Study of MgB$_{2}$ Films for RF Cavity Applications

Magnesium diboride (MgB$_{2})$ is a promising superconducting material for RF cavity applications due to its high critical temperature $T_{c}$ and large thermodynamic critical field $H_{c}$. Using Hybrid Physical-Chemical Vapor Deposition (HPCVD), we have grown 2"-diameter MgB$_{2}$ films on sapphire and metal substrates, including molybdenum, niobium, tantalum, and stainless steel. Measured by DC magnetization, the $T_{c}$'s of these films were between 38.2 to 39.2 K; the upper critical field $H_{c2}$'s were about 7 T, in consistent with previously reported value of clean MgB$_{2}$ films; the zero-field critical current density $J_{c}$'s were above 10$^{7}$ A/cm$^{2}$ and were suppressed rapidly by increasing applied magnetic field, indicating a lack of pinning in clean MgB$_{2}$ films. Multilayered MgB$_{2}$/MgO films were also investigated to prevent vortex penetrating the MgB$_{2}$ layer and increase the vortex penetration field (H$_{c1})$ following Gurevich's theoretical work [1]. The RF properties of these films were studied. \\[4pt] [1] A. Gurevich, \textit{Appl. Phys. Lett.} 88, 012511 (2006).