Preparation and magnetic properties of rare earth garnets and apatites

It has been found possible to prepare garnets with magnetic trivalent rare earth ions filling all or most dodecahedral sites while nonmagnetic Sc3+ ions fill all octahedral sites and magnetic Fe3+ ions fill all or most tetrahedral sites. Phase-pure garnets found include {RE3-yScy}[Sc2](Fe3)O12, where RE is Sm, Eu, Gd, Tb or Dy and y can be zero with Sm and Eu; {Nd3}[Sc2](FezGa3-z)O12; and other Nd-Sc-Fe garnets of the type {Nd3-(w+y)MwScy}[Sc2](Fe3)O12, where M is Gd, Y, and Lu. Compositions chosen for magnetic studies were those with maximum allowable concentrations of magnetic ions on the dodecahedral and tetrahedral sites. In each case, dependence of magnetization on temperature was measured between room temperature and that of liquid helium. Measurements were also made at liquid helium temperature of the dependence of magnetization on applied field with values up to 60 k0e. Ordering ascribed to ferrimagnetism and perhaps also antiferromagentism has been observed. Saturation has not been obtained with the maximum field applied, apparently because of canting of magnetic ion moments when the octahedral sites contain only diamagnetic ions. Calculations of structure factors have confirmed the structural formulae {Nd2.7Yb0.3}[Yb2](Ga3)O12 and Pr3 [Lu2] (Ga3)O12; that is, rare earths fill all dodecahedral and octahedral sites. Oxyapatites are typified by Ca4La(PO4)3O and Ca Y4(SiO4)3O (or A5B3O13) and Ca5(PO4)3O0.5[]0.5 (or A5B3O12.5), where [] represents a vacancy. Such oxyapatites have in each formula unit as written here three A cations with one type of coordination and the other two another type, three tetrahedral B cations, and 13 or 12.5 oxide ions. These ionic ratios (3:2:3:13-12.5) are therefore very close to those found in garnets (3:2:3:12). Attempts were made to prepare rare earth-iron apatites in order to seek magnetic interactions like those in garnets, but apatites did not form