Temperature and Magnetic Field Dependences of Flux Pinning Force in High-T_c Superconductor Tl_2Ba_2Ca_2Cu_3O_x

The magnetic flux pinning force in Tl 2 Ba 2 Ca 2 Cu 3 O x high-T c superconductor (T c =120 k) were measured as functions of temperature and magnetic field by using a torque magnetometry. The magnetic torque curves exhibit a large rotational hysteresis accompanied with a delayed angle for the rotation of applied magnetic fields