Hydrothermal and high-pressure preparation of some BaMnO 3 modifications and low-temperature magnetic properties of BaMnO 3(2H)

Abstract

Three modifications of barium manganese oxide, BaMnO 3(2H), BaMnO 3(9R), and BaMnO 3(4H), were prepared using hydrothermal and high-pressure techniques. The crystal structure of BaMnO 3(2H) was refined using X-ray and neutron-diffraction powder patterns. The structure is hexagonal with space group P6 3 mmc, and a = 5.694, Å, c = 4.806, Å. The magnetic properties of BaMnO 3(2H) were investigated between 2.4° and 273°K in a magnetic field of 9750 Oe. The compound is antiferromagnetic with a Néel temperature of less than 2.4°K. Neutron-diffraction powder patterns were obtained at 1.8°K and 300°K. Three weak magnetic superlattice reflections were indexed on the basis of a hexagonal unit cell with the dimensions a H = a√3, and c H = c, where a and c are the dimensions of the chemical unit cell. A collinear antiferromagnetic arrangement of the spins parallel to the [001] direction describes the magnetic structure.