2D to 3D Magnetism in Synthetic Micas

Fe-based mica minerals usually display two opposing magnetic ground states, either they behave as spin-glasses or as layered ferrimagnets. No definite reason has been proposed as an explanation for this duality. This conundrum is unraveled by comparing the synthetic micas KFe3[MGe3]O10X2 with M & boxH;Fe and Ga, X & boxH;OH- and F-. Neutron diffraction demonstrates a 2D to 3D magnetic transition in KFe3[FeGe3]O10(OH)2 while just hints or no order at all are observed for the fluorides with M & boxH;Fe and Ga respectively. The 3D transition is triggered by the presence of iron in the intralayer tetrahedra. DFT+U calculations show that the magnetic exchange couplings between the previously believed solely magnetic octahedral layers would otherwise be frustrated without this intralayer iron. 2D to 3D magnetic transition in KFe3[FeGe3]O10(OH)2 synthetic mica is observed. This occurs thanks to the intralayer tetrahedral Fe, which couples antiferromagnetically with the otherwise frustrated octahedra layer. image