We report the synthesis, crystal structure, and thermal, dielectric, phonon, and magnetic properties of [NH₂-CH⁺-NH₂][Mn(HCOO)₃] (FMDMn). The anionic framework of [(Mn(HCOO)₃^–] is counterbalanced by formamidinium (FMD⁺) cations located in the cavities of the framework. These cations form extensive N–H···O hydrogen bonding with the framework. The divalent manganese ions have octahedral geometry and are bridged by the formate in an anti–anti mode of coordination. We have found that FMDMn undergoes a structural phase transition around 335 K. According to the X-ray diffraction, the compound shows R3̅c symmetry at 355 K and C2/c symmetry at 295 and 110 K. The FMD⁺ cations are dynamically disordered in the high-temperature phase, and the disorder leads to very large bandwidths of Raman and IR bands corresponding to vibrations of the NH₂ groups. Temperature-dependent studies show that the phase transition in FMDMn is associated with ordering of the FMD⁺ cations. Detailed analysis shows, however, that these cations still exhibit some reorientational motions down to about 200 K. The ordering of the FMD⁺ cations is associated with significant distortion of the anionic framework. On the basis of the magnetic data, FMDMn is a weak ferromagnet with the critical temperature T_c = 8.0 K.

We report on a comprehensive study of ${\mathrm{CePd}}_{1-x}{\mathrm{Rh}}_x$ ($0.6\le x\le 0.95$) poly- and single crystals close to the ferromagnetic instability by means of low-temperature ac susceptibility, magnetization, and volume thermal expansion. The signature of ferromagnetism in this heavy-fermion system can be traced from 6.6 K in CePd down to 25 mK for $x=0.87$. Despite pronounced non-Fermi-liquid effects in both specific heat and thermal expansion, the Grüneisen ratio does not diverge as $T\to 0$, providing evidence for the absence of a quantum critical point. Instead, a peculiar “Kondo-cluster-glass” state is found for $x\ge 0.65$, and the non-Fermi-liquid effects in the specific heat, ac susceptibility, and magnetization are compatible with the quantum Griffiths phase scenario.

We report the synthesis and characterization of a novel metal formate templated by dimethylammonium cations, [(CH ₃ ) ₂ NH ₂ ][Na _0.5 Fe _0.5 (HCOO) ₃ ], exhibiting phase transition at 167 K.