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The low-temperature heat capacity of lanthanide-doped (La, Nd) and americium-doped UO 2 samples was measured by calorimetry. The results showed a strong effect on the antiferromagnetic C p 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 ( La 3 + , Nd 3 + , Am 3 + ) leads to a split of the λ peak, for which we hypothesize that the clustering of the trivalent ions with the charge compensator pentavalent U 5 + can play a role. The overall behavior is confirmed by magnetization measurements using SQUID. The observed differences between La 3 + , Nd 3 + , and Am 3 + are attributed to the f – f exchange interaction. 241 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 α dose). The observed effects are similar to 238 Pu-doped UO 2 , the slight differences being attributed to a higher degree of disorder in the Am material. [ABSTRACT FROM AUTHOR]

The reduction of UVI uranyl halides or amides with simple LnII or UIII salts forms highly symmetric, linear, oxo-bridged trinuclear UV/LnIII/UV, LnIII/UIV/LnIII, and UIV/UIV/UIV complexes or linear LnIII/UV polymers depending on the stoichiometry and solvent. The reactions can be tuned to give the products of one- or two-electron uranyl reduction. The reactivity and magnetism of these compounds are discussed in the context of using a series of strongly oxo-coupled homo- and heterometallic poly(f-block) chains to better understand fundamental electronic structure in the f-block. [ABSTRACT FROM AUTHOR]

Single-chain magnets (SCMs) are materials composed of magnetically isolated one-dimensional (1D) units exhibiting slow relaxation of magnetization. The occurrence of SCM behavior requires the fulfillment of stringent conditions for exchange and anisotropy interactions. Herein, we report the synthesis, the structure, and the magnetic characterization of the first actinide-containing SCM. The 5f-3d heterometallic 1D chains [{[UO2(salen)(py)][M(py)4](NO3)}] n, (M=Cd ( 1) and M=Mn ( 2); py=pyridine) are assembled trough cation-cation interaction from the reaction of the uranyl(V) complex [UO2(salen)py][Cp*2Co] (Cp*=pentamethylcyclopentadienyl) with Cd(NO3)2 or Mn(NO3)2 in pyridine. The infinite UMn chain displays a high relaxation barrier of 134±0.8 K (93±0.5 cm−1), probably as a result of strong intra-chain magnetic interactions combined with the high Ising anisotropy of the uranyl(V) dioxo group. It also exhibits an open magnetic hysteresis loop at T<6 K, with an impressive coercive field of 3.4 T at 2 K. [ABSTRACT FROM AUTHOR]

Abstract: We have investigated oriented single crystals of the antiferromagnets NpCoGa5 (T N≈47K) and NpRhGa5 (T N≈36K) and the superconductors PuCoGa5 (T c≈18K) and PuRhGa5 (T c≈9K) by magnetization and specific heat measurements. Significant anisotropy effects are observed : when magnetic fields are applied in the basal plane, the Néel temperatures of NpCoGa5 and NpRhGa5 are barely affected. On the contrary, in fields applied along the c-axis, NpCoGa5 undergoes a metamagnetic transition to an induced ferromagnet and in NpRhGa5 the second-order transition (magnetic ordering) is shifted to lower temperatures and merges into the first-order transition (reorientation of the magnetic moments). This study reveals the analogy in AnTGa5 compounds between antiferromagnetic order and superconductivity that are both more fragile when the magnetic field is applied along the c-axis, consistent with antiferromagnetic fluctuations mediated superconductivity in PuCoGa5 and PuRhGa5. [Copyright &y& Elsevier]