Complete Range Of Solid Solutions Research Articles

Crystal chemical and magnetic studies of garnet systems: [formula omitted

A complete solid-solution range exists in the system {YCa 2}[Zr 2](Fe 3)O 12{Y 3}[Fe 2](Fe 3)O 12. The Zr 4+ ion is even larger than the Sn 4+ ion and in this system apparently prefers only the octahedral sites. The behavior of the plot of n B (∞,0) vs. composition is similar to that of the Ca 3Fe 2Sn 3O 12Y 3Fe 2Fe 3O 12 system and corroborates the interaction model for garnets recently derived by gilleo. A small spontaneous magnetization is observed in the garnets {YCa 2}[Zr 2](Fe 3)O 12 and {YCa 2}[Zr 2](Me 0.5Fe 2.5)O 12, Me = Al and Ga, indicating the es of magnetic sublattices among the tetrahedral sites. The garnet {YC a2}[H f2](Fe 3)O 12 is readily formed. The Hf 4+ ion, which is very nearly the same size as that of Zr 4+, also prefers the octahedral site.

Crystal chemical and magnetic studies of garnet systems M32+Fe 2Sn 3O 12—Y 3Fe 2Fe 3O 12

A complete solid-solution range exists in the system Ca 3Fe 2Sn 3O 12(CIS)—Y 3Fe 2Fe 3O 12 (YIG). Because of its large size, the Sn 4+ ion prefers the octahedral positions; thus for dilute solutions of CIS in YIG the saturation magnetization at 0°K increases. A maximum of 7.3 μ b per formula unit is reached at about 20 mol. percent CIS solid solution. However, the plot of n b (∞, 0) vs. composition deviates markedly from that which depends only on a simple interaction model. At 33 mol. per cent CIS, n B = 5.2 μ B , and at 50 mol. per cent, n B = 1.2 μ B , even though the Sn 4+ ions are very nearly all in the octahedral sites. At 67 mol. per cent CIS, 90 per cent of the octahedral sites are filled with Sn 4+ ions, as determined by X-ray diffraction, and n B ≈ 0.25 μ B . The magnetic behavior of this system may be explained on the basis of the reduction of the number of octahedraltetrahedral magnetic-ion interactions with increasing concentration of CIS and, at the higher concentrations, the establishment of two magnetic sublattices among the tetrahedral ions. No other end-members M 3 2+Fe 2Sn 3O 12 were obtained, but with M = Sr the extent of solubility in YIG is ∼ 33 mol. per cent, and when M = Ba, < 5 mol. per cent. Some inconclusive experiments also indicated some solution when M = Cd, Zn, Mn, Ni and Mg.

Crystallographic and magnetic properties of several spinels containing trivalent ja-1044 manganese

Many useful ferrimagnetic oxides which crystallize with the spinel structure contain several transition metals, each of which can exist in two or more possible oxidation states. A specific formulation for many such materials is very difficult. An approach to this problem, in some cases, can be made through crystallographic studies. The tetragonal distortion from cubic symmetry exhibited by several spinels containing manganese has been attributed to characteristic properties of Mn 3+ ions occupying the octahedral positions in the lattice. Several new compositional systems containing manganese and crystallizing with the spinel structure have been prepared and studied crystallographically and magnetically. The following solid-solution systems were chosen because they appeared to present a minimum of ambiguity in composition and in the distribution of cations among tetrahedral and octahedral positions: Zn x Ge 1− x Mn 2O 4, Zn x Ge 1− x Co 2−2 x Mn 2 x O 4, and Zn x Li 1− x Mn 2O 4. The tetragonal distortions from cubic symmetry observed for these systems can be accounted for by assuming that the octahedral sites are occupied by more than a critical fraction, 60–65 per cent, of Mn 3+ ions. A complete range of solid solutions in the system Co 3− x Mn x O 4 was prepared and formulas assigned on the basis of this rule. The configuration, for values of x between 0 and 2, appears to be Co 3+[Co 3+ 2− x Mn x 3]O 4. The observed magnetic properties (saturation magnetization at 4.3°K and Curie temperatures) can be interpreted in terms of this configuration. The magnetization measured for cubic materials is the result of Néel-type magnetic coupling between Co 2+ ions on tetrahedral sites and Mn 3+ ions on octahedral sites. Tetragonal materials apparently have a more complex magnetic structure. The configuration of Co 3−x Mn x O 4 for values of x between 2 and 3 appears to be Co 2+ 3− x Mn 2+ x −2 [Mn 3+ 2]O 4. The crystal-lattice constants, saturation magnetization (4.3°K) and Curie temperatures are given for a number of materials, including GeMn 2O 4, LiMn 2O 4, Co 3O 4, MnCo 2O 4, CoMn 2O 4, and Mn 3O 4.