Determination of the Exchange Integrals in β-MnO₂

Abstract

Magnetic susceptibility and specific heat of the β-MnO₂ powder specimen have been measured in the range 20 to 300°K and 77 to 100°K respectively. The measurements have also been made for the paramagnetic inelastic neutron scattering at room temperature by using time-of-flight method. The values of the Weiss temperature, of the Néel temperature and of the average full width at half maximum of the neutron energy distribution (Gaussian) have been determined as 1050°K, 92°K and 13 meV respectively. The exchange integrals (J_n) are determined by combining these experimental data with the theoretical relations between exchange interactions and physical properties and by assuming J₁⁄J₂=1.60: J₁=8.9 (antiferromagnetic), J₂=5.5 and J₃=−1.3°K, where J₁ is the exchange integral between nearest neighbours (in the ⟨001⟩ direction), J₂ acts between next nearest neighbours (⟨111⟩ direction) and J₃ refers to third-neighbour coupling.