Magnetic cluster excitations in the antiferromagnetic phase of α-MnMoO4 -: art. no. 092410

The tetramer-based compound alpha-MnMoO4 exhibits four prominent peaks in the inelastic neutron scattering (INS) spectrum between 0.5 and 2.0 meV below 10 K. They are assigned to magnetic excitations of the (Mn2+)(4) rhombus shaped cluster, with resulting values of the exchange parameters J=+0.051 meV and J(')=-0.019 meV along the edges and the short diagonal, respectively. The interactions within the tetramer are treated exactly in an isotropic quantum mechanical model leading to an S=10 cluster ground state. The weaker antiferromagnetic (AFM) intercluster interactions, J(int)=-4.5x10(-3) meV, are treated in a molecular-field model below the AFM transition temperature T-N=10.7 K. INS and susceptibility are in quantitative agreement with this approach.