Abstract
Low-field ac measurements of magnetic susceptibility of YBa
2Cu
3O
7 high-temperature superconducting thin film were carried out over a wide range of temperatures and ac magnetic field amplitudes. A strong field dependence of the real
χ′ and imaginary
χ″ components was observed. The field dependence of the imaginary component is used to extract the temperature dependence of the critical current density in the sample using the critical state model. The exponent
β of the power law relation
J
c
∼
(1
−
T/
T
c
)
β
was determined from ac-susceptibility data and different values were found. Experimental results are compared with predictions of some existing theoretical models describing the ac response of superconducting thin film in perpendicular ac field.