Magnetization of superconducting thin films in a transverse field and a lower critical field extraction

The derivation of the lower critical field H c1 through magnetization measurements for the samples yielding large demagnetization effect is discussed. SQUID magnetometry and circular thin film samples are taken in mind but results are applicable more widely. The conclusion is drawn out that only an upper limit for H c1 can be estimated thus eliminating the confidence of the published data obtained for thin films and platelike crystals.