Plutonium aging leads to the creation of decay products, such as americium, uranium, helium, but also to self-irradiation defects such as vacancies and interstitials. These self-irradiation defects can affect the properties of plutonium; as an example, swelling of PuGa or PuAl alloys has been observed at room temperature. This work is devoted to the study of the effect of aging on the magnetic susceptibility of pure and alloyed plutonium. An anomaly has been revealed at low temperatures (T ≤ 75K) for magnetic fields lower than 4.5 T. This anomaly decreases after heat treatment. A tentative explanation, based on results from molecular dynamics calculation in δ-plutonium, is given to explain the origin of the anomaly.