Lateral spin valve (LSV) device consists of two ferromagnetic (FM) wires connected by a non-magnetic (NM) wire is one of the candidates for read sensors for the next generation ultrahighdensity magnetic recording system exceeding the areal density of 2 Tbit/in. Co-based Heusler alloys are promising spin polarized electron sources for such spintronic devices due to their high Curie temperature and theoretically predicted half-metallicity. The crystal structure is the L21-ordered full-Heusler but the atomic order is often imperfect that can deteriorate the highly spin-polarized electronic structure. The negative scattering length of Mn atoms using elastic neutron diffraction makes this technique ideally suited to study the site swapping of Co and Ni elements with Mn. We wish to compare the atomic order of 3 compositions in powder form that show large magnetoresistance in LSV devices.