Low-temperature heat capacity and magnetism in (U_1−yLn_y)O₂ and (U_1−yAm_y)O₂ (y = 0.01 − 0.05) solid solutions: Effects of substitution and self-irradiation

The low-temperature heat capacity of lanthanide-doped (La, Nd) and americium-doped [Formula: see text] samples was measured by calorimetry. The results showed a strong effect on the antiferromagnetic [Formula: see text] anomaly as a result of crystal lattice substitution, defects resulting from self-irradiation, and electron interaction. It was found that the substitution of trivalent ions ([Formula: see text], [Formula: see text], [Formula: see text]) leads to a split of the [Formula: see text] peak, for which we hypothesize that the clustering of the trivalent ions with the charge compensator pentavalent [Formula: see text] can play a role. The overall behavior is confirmed by magnetization measurements using SQUID. The observed differences between [Formula: see text], [Formula: see text], and [Formula: see text] are attributed to the [Formula: see text]–[Formula: see text] exchange interaction. [Formula: see text]Am decay causes in addition self-irradiation effects (point defects), and reduces Néel temperature, peak intensity, and magnetic entropy as a function of decay (accumulated [Formula: see text] dose). The observed effects are similar to [Formula: see text]Pu-doped [Formula: see text], the slight differences being attributed to a higher degree of disorder in the Am material.