2, Nagoya University, Nagoya, , Japan
3, Nagoya University, Nagoya, , Japan
NdFeAs(O,F) thin films of around 50 nm thickness were grown by molecular beam epitaxy on MgO single crystal. The F doping was achieved by F-diffusion from a NdOF over-layer into the undoped NdFeAsO layer. The film showed a sharp cube-on-cube texture. Electrical transport properties were measured on laser-cut micro-bridges in 4-point geometry and maximum Lorentz force configuration in magnetic fields up to 14 T.
The T-dependent E(J) curves at constant magnetic field can by scaled within the framework of the vortex glass-liquid transition. Best scaling is achieved for 3D and critical exponent ν ~ 1.3 and z ~ 9. Whereas ν is in the expected range of 1.0-2.0, z is slightly above the expected range of 4.0-6.0. The reason for this increased value might lie in the distribution of pinning energies and, hence, local Jc variation. The activated flux motion within the vortex liquid range is characterized by analyzing the scaling behavior of the temperature-dependent resistivity curves as well as their derivatives.
The work was partly supported by the JSPS Grant-in-Aid for Scientific Research (B) Grant Number 16H04646.