Magnetic field of BG-VG transition depending on the nanorods shape in BaHfO₃-doped SmBa₂Cu₃O_y films

The vortex state under the magnetic field around vortex glass (VG) - Bose glass (BG) transition field was investigated in the SmBa₂Cu₃O_y (SmBCO) films with BaHfO₃ (BHO) nanorods. We prepared two films with different forms of the nanorods (thick-straight and thin-tilted), and we used the magnetic field angular dependence of flux flow resistivity (ρ - Θ) to identify a vortex state. From a comparison between the ρ - Θ curves in completely BG and VG phases, it was revealed that the existence of deep and sharp dip structure along the c-axis direction of the SmBCO matrix (B//c) was an evidence of the BG state in both the films. In the magnetic field region around VG-BG transition, shallower and broader dips than the dips in the BG state were observed at B//c in both the films. In addition, the dips became deeper with increase of the magnetic field in this region in each film. Therefore, we considered the vortex state of both the films was an intermediate and/or a transient state of BG and VG. Under all magnetic fields, the film with thick and straight BHO nanorods showed stronger c-axis correlated flux pinning force than the film with thin and tilted nanorods. We suggested the intermediate state of the film with thicker and straighter nanorods was similar to the BG state compared with another film from the both of experimental results and reported theory.