Neutron Diffraction Study of Helimagnet (Ba_1−xSr_x)₂Zn₂Fe₁₂O₂₂

Abstract

Neutron diffraction experiments were carried out on a single crystal of (Ba_1−xSr_x)₂Zn₂Fe₁₂O₂₂, x=0.748, at 77 and 296 K. The turn angle of the helix, φ₀, is 81.6° at 77 K and 135° at 296 K. The helix consists of large and small ferrimagnetic spin-bunches separated by an angle of φ₀⁄2 in the c-plane. Their magnitudes are 4.32 μ and 0.32 μ, respectively. Here, μ is the magnetic moment per Fe ion: μ=4.66 μ_B at 77 K and μ=1.86 μ_B at 296 K. These results are discussed from a point of view of the super-exchange interaction.