In accordance with the results of our previous research, a low-temperature growth (LTG) technique is effective for expanding the lower growth temperature region of c-axis-orientated SmBa2Cu3Oy (SmBCO) thin films. However, BaHfO3 (BHO)-doped LTG films show a marked decrease in Jc at low magnetic fields compared with conventional PLD films. In this study, we aimed to clarify the mechanism of Jc decrease and investigated the thickness dependence of the seed layer on the (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) (100) single crystal. The obtained results indicate that Jc decreased at low magnetic fields as the thickness of the seed layer increased. It is suggested that flux line kinks produced by flux motion in the seed layer would lead to the depinning of flux lines from BHO nanorods in the upper layer. Thus, we added Y2O3 into the seed layer to trap flux lines in the seed layer. Consequently, we improved Jc in the low magnetic field region even in the films prepared by using the LTG technique.