Weak ferromagnetism in Ba 2Cu 3−xCo xO 4Cl 2 ( [formula omitted]) and Ba 2−ySr yCu 3O 4Cl 2 ( [formula omitted

Abstract

Magnetization measurements were carried out for the oxychlorides Ba 2Cu 3− x Co x O 4Cl 2 ( 0 ⩽ x ⩽ 0.1 ) and Ba 2− y Sr y Cu 3O 4Cl 2 ( 0 ⩽ y ⩽ 2 ) with lamellar structure. The weak ferromagnetic moment observed in Ba 2Cu 3O 4Cl 2 increased drastically by substitution of a small amount of Co for Cu, in contrast with the case of Ni substitution where the moment disappears sharply by a small substitution of Ni. In the case of Ba 2− y Sr y Cu 3O 4Cl 2, although the substitution was made not for the magnetic Cu ion but for the non-magnetic Ba ion, the weak ferromagnetic moment decreased gradually by substitution and at the same time the Néel temperature increased. We suggest that these extreme changes of the weak ferromagnetism in the Ba 2Cu 3O 4Cl 2 system are caused by the conflicting magnetic interactions in two Cu sublattices.