Magnetic interactions in α-MnSeO4, α-FeSO4, and β-FeSO4

The energy distributions of neutrons scattered by α-MnSeO4, α-FeSO4, and β-FeSO4 in their paramagnetic state are measured by means of a time-of-flight technique. The values of two exchange parameters can be estimated from a simultaneous analysis of the second moment of these energy distributions and of the Neel temperature computed in the Green's function approximation. Various two-parameter analyses are performed and checked by comparing calculated and experimental values for theta and chi(Tsub(N)). For α-FeSO4 the dominant interactions occur between the first and second neighbours. For β-FeSO4 two-parameter analyses do not lead to a satisfactory description of all data; however, one can conclude that the interactions between third neighbours are important, in agreement with the stability conditions for the observed spin configuration. (author)