Effect of electron doping on the magnetic dynamics of the d^4 Mott insulator Ca2RuO4

Oxides containing heavy transition-metal ions with four d electrons (d^4) surrounded by an octahedron of oxygen ions have recently been predicted to display a novel type of magnetic order called excitonic magnetism. The conditions required for this state are that the atomic spin-orbit coupling is comparable in strength to the magnetic coupling between neighbouring ions. A recent theoretical study predicted that excitonic magnetism can be found in Ca2RuO4, and that as a result the inter-site interactions are strongly modified by electron doping. We aim to investigate this prediction by comparing the spin dynamics of Ca2RuO4 with that of compounds doped with 5% of La and Pr. The spectrum of spin excitations is sensitive to the sign and magnitude of the inter-site coupling and also to the strength of the spin-orbit coupling, so by identifying changes in these we will test the predictions.