The Disordered High-Temperature Structure of (NH4)3H(SO4)2 and Its Relationship to the Room-Temperature Phase

Magnetic data are presented for LnMnO3 (Ln=Ho, Er, Tm, Yb, and Lu) having the hexagonal crystal structure of P63cm. DC magnetization measurements show that magnetic order is not clearly observed for Ln=Ho–Yb, while an antiferromagnetic transition of the Mn3+ moments is found at ~90 K for LuMnO3, where the Lu3+ ion has no 4f localized moment. This is ascribed to both the paramagnetism of Ln3+ and the suppression of magnetization in the Mn3+ sublattices arising from strong antiferromagnetic interactions between Mn3+. Deviation from the Curie–Weiss law at low temperatures indicates the onset of antiferromagnetism. Some magnetization data of Ca-substituted compounds, Ln0.5Ca0.5MnO3, which have the different crystal structure of orthorhombic Pnma, are also discussed briefly.