Why the pyrochlore-like antiferromagnet NaCu 3 F 7 is magnetically non-frustrated.

We present a theoretical study of the magnetic properties for the pyrochlore-like NaCu 3 F 7 compound, which surprisingly experience little or no frustration. The magnetic effective exchange interactions were calculated using ab-initio methods explicitly treating the electronic correlation. A model Hamiltonian was built from these interactions and used to determine the zero temperature magnetic order versus magnetic field, using a quantum Heisenberg Hamiltonian or, for comparison, a spin 1/2 Ising Hamiltonian. The magnetic order at zero magnetic field is non frustrated and associated with the propagation vector q = (0,0,0). The magnetization versus magnetic field reveals the existence of a 1/3 plateau that could be observed in high-pulsed magnetic field experiments. Analysing the magnetic interactions, we highlight the importance of the magnetic-ion nature and the lattice distortion, in the non-frustrated nature of the NaCu 3 F 7 magnetic structure, despite its triangular/Kagome subnetworks. We believe that this non-frustrated behaviour could also take place in other triangular copper-based systems.&#xD.