The static magnetic susceptibility of two different YBa₂Cu₃O_6.30 samples has been measured at different fields in the range 2 - 300 K, using a superconducting quantum interference device magnetometer; one sample has been prepared by oxygen intercalation, the other one by deintercalation. The susceptibility shows a peak near 45 K in both samples, which depends on the field and the magnetic history. The susceptibility of semiconducting and superconducting compounds, with an oxygen content O_6.20 and O_6.41, respectively, has also been investigated. The presence of the peak in the YBa₂Cu₃O_6.30 samples has been explained by the combined effect of regions with a Curie-like behaviour and superconducting regions. The origin of these regions is discussed.