Magnetic ordering in diluted kagome antiferromagnets

Potassium iron jarosite, KFe3(SO4)(2)(OH)(6), provides a model kagome Heisenberg antiferromagnet with which to study the behaviour of this highly frustrated system. Magnetic susceptibility, powder neutron diffraction and muon spin relaxation measurements have been performed on samples of protonated and deuterated potassium iron jarosite in which some of the iron is replaced by aluminium ions to study the effect of diamagnetic dilution. The two successive magnetic ordering transitions of the pure material drop in temperature on doping. In all cases the low temperature phase appears to have long-range ordering of all moments in an array which is coplanar or nearly coplanar with the crystallographic ab axes, while in the intermediate phase there is a component of moment along the c-axis and some degree of dynamic character.