Electron spin resonance study of γirradiated cadmium formate dihydrate and manganese(II) ions in cadmium formate dihydrate Several dihydrated formates inciuding:Ni (HCOO)2' 2Ht) and Fe(HCOOh·2H20 crystallize in a monoclinic structure whose unit cell contains two each of two inequivalent types of metal ions. The temperature variation of the powder susceptibility, Xp, of the Ni+ + salt suggests that those ions on one type of site become cooperatively ordered near 15.7°K while the rest remain essentially independent even at 1.3°K. XP for the Fe+ + salt exhibits a huge peak at 3.68°K associated apparently with the long-range ordering of moments on sites of both types. Mossbauer experiments at 300 0 K on the Fe+ + salt clearly distinguish ions on the two sites, the ratio of the effective electric}ield gradients being ",5 to 1. The smaller field gradient is assumed to characterize the site (type 1) . approximately octahedrally coordinated by oxygens from six formate groups. The Mossbauer spectrum near the transition point differs from those measured at 300°, 77°, 20 0 , and 4°K, The results show that the internal magnetic field is larger at the type 1 sites. Preliminary calculations uiing the observed nuclear hyperfine structure indicate that the ratio of magnetic fields at the two sites is about four to one.

No abstract

No abstract