Magnetic Structure of (Ba_1−xSr_x)₂Zn₂Fe₁₂O₂₂ (x=0–1.0)

Abstract

Neutron and X-ray diffraction studies and magnetization measurements were carried out on single crystals of (Ba_1−xSr_x)₂Zn₂Fe₁₂O₂₂. The substitution of Ba by Sr produces two effects on the crystal structure: a lattice deformation around the Sr ions and a redistribution of the Zn and Fe ions in the tetrahedral sites. The magnetic structure is analyzed in consideration of these effects: Spins are bunched in the form of ferrimagnet in the every (T_1⁄2ST_1⁄2) block and the bunched spins make an angle φ₀ between the adjacent (T_1⁄2ST_1⁄2) blocks. At 294 K, the turn angles φ₀’s are found to be 0° (ferromagnetic), 0°<φ₀<180° (helical) and 180° (antiferromagnetic) for 0≤x≤0.5, 0.5<x<0.8 and 0.8\lesssimx≤1.0, respectively. A brief discussion on the exchange interaction of this spin system is given.