High field properties of superconducting nb3ge films prepared by chemical vapor deposition

The superconducting critical current densities Jc of Nb3Ge films prepared by chemical vapor deposition have been investigated in magnetic fields parallel and perpendicular to the film plane up to above 20 T. The Jc and its field dependence are strongly influenced by any change in the microstructure of films deposited at different deposition temperatures Td. Films deposited at a low Td of 800ŶC exhibit a high Jc below 20 T and show a slight difference between parallel and perpendicular field dependences of Jc. As Td is increased to 900ŶC, the Jc of films is appreciably lowered over the entire field range and the difference between two field dependences of Jc is remarkably enlarged. The upper critical field Hc2 of these films has been obtained by extrapolating the Kramer plot of Jc^1/2H^1/4versus H to J^1/2cH^1/4=0, and were estimated to range from 28 to 31 T at 4.2 K.