Helical magnetic ordering in Sr(Co1−xNix)2As2

J. M. Wilde, A. Kreyssig, D. Vaknin, N. S. Sangeetha, Bing Li, W. Tian, P. P. Orth, D. C. Johnston, B. G. Ueland, R. J. McQueeney
2019 Physical review B  
SrCo2As2 is a peculiar itinerant magnetic system that does not order magnetically, but inelastic neutron scattering experiments observe the same stripe-type antiferromagnetic (AF) fluctuations found in many of the Fe-based superconductors along with evidence of magnetic frustration. Here we present results from neutron diffraction measurements on single crystals of Sr(Co1-xNix)2As2 that show the development of long-range AF order with Ni-doping. However, the AF order is not stripe-type. Rather,
more » ... the magnetic structure consists of ferromagnetically-aligned (FM) layers (with moments laying in the layer) that are AF arranged along c with an incommensurate propagation vector of (0 0 tau), i.e. a helix. Using high-energy x-ray diffraction, we find no evidence for a temperature-induced structural phase transition that would indicate a collinear AF order. This finding supports a picture of competing FM and AF interactions within the square transition-metal layers due to flat-band magnetic instabilities. However, the composition dependence of the propagation vector suggests that far more subtle Fermi surface and orbital effects control the interlayer magnetic correlations.
doi:10.1103/physrevb.100.161113 fatcat:s462h2ilbfdovis2tx3oou75vq