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Abstract

Themagnetism ofmagnetoelectric S = 3/2 pyroxenes LiCrSi2O6 and LiCrGe2O6 is studied by density functional theory calculations, quantum Monte Carlo (QMC) simulations, neutron diffraction, as well as low-and high-field magnetization measurements. In contrast with earlier papers, we find that the two compounds feature remarkably different, albeit nonfrustrated magnetic models. In LiCrSi2O6, two relevant exchange integrals, J(1) similar or equal to 9 K along the structural chains and J(ic1) similar or equal to 2 K between the chains, form a two-dimensional anisotropic honeycomb lattice. In contrast, the spin model of LiCrGe2O6 is constituted of three different exchange couplings. Surprisingly, the leading exchange J(ic1) similar or equal to 2.3 K operates between the chains, while J(1) similar or equal to 1.2 K is about two times smaller. The additional interlayer coupling J(ic2) similar or equal to J(1) renders this model three dimensional. QMC simulations reveal excellent agreement between our magnetic models and the available experimental data. Underlying mechanisms of the exchange couplings, magnetostructural correlations, as well as implications for other pyroxene systems are discussed.