AC Susceptibility of the $YBa_2Cu_3O_7$ Coated Conductor in High Magnetic Fields

The AC susceptibility of the $YBa_2Cu_3O_7$ coated conductor in the perpendicular applied AC magnetic field was investigated using an inductive experimental setup with a pair of coils connected in opposite. A harmonic homogeneous AC magnetic field was applied perpendicularly to the wide face of the $YBa_2Cu_3O_7$ coated tape. Together with this AC field, a parallel background DC magnetic field up to 14 T was applied perpendicularly to the tape. The measurements were performed at several constant temperatures in the range 3-50 K. In the region of high background DC fields (8-14 T) no influence of the tape's ferromagnetic substrate was detected, despite of the low measurement temperatures employed. The estimate of the critical current density $(j_c)$ at 20 K and 14 T, based on the position of the imaginary AC susceptibility peak, gives the value $j_c$=0.53 MA/$cm^2$.