Character of magnetic instabilities in CaFe₂As₂

The density-functional spin susceptibility has been analyzed in different phases of CaFe₂As₂ and compared with similar data for pure d metals. The conditions for the “no local-moment” itinerant state with large frustrations are found for the “collapsed” phase. This itineracy determines the instability versus the incommensurate magnetic order for the narrow region of wave vectors. For the ambient pressure phase, the local moments on Fe atoms with much less frustrated antiferromagnetic interactions are stabilized and a magnetic short-range or long-range order is developed. The system is close to the point of magnetic instability and spin fluctuations should be included to describe properties of this system.