Influence of Cr-doping on the magnetic structure of the FeAs strip compounds CaFe4As3 : a single crystal neutron diffraction study

CaFe$_4$As$_3$ offers the unique opportunity to modify the topology of the Fe$_2$As$_2$ layers, key in the understanding of superconductivity in the new iron pnictide superconductors, from infinite layers to strips of finite width linked a rectangular cross pattern. Bulk measurement on CaFe$_4$As$_3$ indicate a magnetic ordering at ~90K with a second transition seen at about 26K. Neutron diffraction allowed to ascribe the high temperature transition to a Spin Density Wave(SDW) with a propagation vector k=(0,$\delta$,0) eventually locking to $\delta$=3/8 at the lower transition. As expected a profound effect on the magnetic properties of CaFe$_4$As$_3$ can be obtained by chemically doping or applying pressure. We report here on the consequence of Cr-doping on the magnetic structure of CaFe$_4$As$_3$ derived from single crystal neutron diffraction.