Magnetic properties of CeM1.5M’0.5Ge4O12 (M = Mn, Co; M’ = Ni, Cu)

Abstract

A study of the solid solutions CeM 2-x M' x Ge 4 O 12 (M = Mn, Co; M' = Ni, Cu) by X-ray diffraction and magnetometry is described. For M = Co the introduction of Ni and Cu was possible for x ≤ 0.5; for M = Mn attempts to introduce Cu were unsuccessful but CeMn 1.5 Ni 0.5 GeO 4 was obtained as a single phase. These compositions crystallise in the space group P4/nbm with a ~9.76, c ~4.85 Å. They all order antiferromagnetically with T N < 10 K.The magnetic structures adopted by CeMn 1.5 Ni 1.5 Ge 4 O 12 and CeCo 1.5 Cu 0.5 Ge 4 O 12 were shown by neutron diffraction to be the same as those adopted by CeMn 2 Ge 4 O 12 and CeCo 2 Ge 4 O 12 , respectively. The in-field metamagnetic transition of the latter to a weakly ferromagnetic phase was shown to persist in the Cu-doped composition. The available data suggest that the anisotropy associated with the Co 2+ cation plays a dominant role in determining the magnetic behaviour of these compounds.

Magnetic properties of GdBB′Ge4O12; BB′ = FeZn or GdCa

“…It is also lower than that of the more magnetically-concentrated composition ErFeCuGe4O12 [9]. The magnetic superexchange pathways that might be important in this crystal structure have been described in detail elsewhere [4]. We assume that the superexchange between d-block cations along Fe -O -Ge -O -Fe pathways is the dominant interaction in these compounds and that the moments of the f-block cations on the 2b sites are aligned by the internal field created at the 4f sites.…”

“…The distribution of the cations over the two sites is determined by their relative size and charge. Our own research has focussed on compositions in which one or more of the cations is magnetic and we have previously reported the occurrence of paramagnetism, spin-glass behaviour, antiferromagnetism and weak ferromagnetism within the structure type [3][4][5][6][7][8]. Paramagnetism is likely to result when only one site is occupied by a magnetic cation, as in Y2CoGe4O12 [3], but the behaviour of the more magnetically-concentrated compositions is difficult to predict because several intercation interactions are in competition with each other.…”