Magnetic structure and exchange integral measurement in TlMnF₃

Abstract

Neutron diffraction patterns of polycrystalline TlMnF₃ from 300°K to 4.2°K indicate that it has a cubic perovskite structure (a₀ = 4.248 Å) which undergoes an antiferromagnetic transition below 76.5°K to a structure of the G-type without any crystallographic distortion. The magnetic moment of the Mn₂₊ ion in this compound is 4.90 μ_B at 42°K. The dominant exchange interaction among the magnetic ions in TIMnF₃ which form a simple cubic lattice is a σ-type superexchange among the nearest neighbors. Under this assumption, the exchange integral has been evaluated by paramagnetic neutron scattering using the moments method of de Gennes. J is found to be 3° ± 0.3°K which is in very good agreement with theoretical calculations.