Competition of itinerant magnetic states in SrCo₂As₂ from RPA spin susceptibility

The square-lattice layered 122-type cobalt pnictides ACo₂Pn₂ (A=Ca, Sr, Eu; Pn=As, P) are metals with fascinating magnetic properties reminiscent of local moment frustration. Among those, SrCo₂As₂ and CaCo₂As₂ stand out due to the competing nature of their in-plane magnetic fluctuations. While CaCo₂As₂ exhibits A-type antiferromagnetic order with ferromagnetically ordered Co planes, inelastic neutron scattering has revealed signs of extreme frustration towards stripe-like antiferromagnetism. SrCo₂As₂ does not order down to T=0.05 K, but shows an intricate competition between ferro- and stripe-like magnetic fluctuations instead. While some of these observations can be rationalized with J₁-J₂-type local moment models, several experimental facts cannot be reconciled within such a local moment picture such an approximate description. Here, we perform a fully itinerant analysis of the magnetic properties of these materials based on a tight-binding model obtained from DFT calculations for the bandstructure. We report our findings on the static transverse spin susceptibility for the resulting multiorbital Hubbard model within the random-phase approximation RPA approximation.