Reduced Dimensionality and Magnetic Frustration in KCr3As3

. Thenon-magnetic state has five Fermi surface sheets involving respectively three quasi-one-dimensionaland two three-dimensional energy bands. However, the ground state is magnetic, exhibiting a novelinterlayer antiferromagnetic order where the basic block-spin state of a unit Cr triangle retains a highspin magnitude. Moreover, its Fermi surface involves three one-dimensional sheets only, providingevidence for local moments in this compound due to the reduced dimensionality. By fitting a twistedspin tube model the magnetic frustrations caused by local moments are found to be relaxed, leadingto gapless spin excitations. A frustration-induced transition to the disordered low block-spin stateis expected upon increasing the intralayer exchange interaction.