Complex magnetic properties of Mn3Ni20P6 and ferromagnetic structure of the new isostructural compound Mn3Pd20P6

A new compound, Mn3Pd20P6, has been synthesized and the crystal and magnetic structures have been determined by neutron powder diffraction. The crystal structure is cubic, with a=11.9563(2)Å, space group Fm3¯m, and is isostructural to Mn3Ni20P6, a ternary ordering variant of the Cr23C6-type structure. The magnetic properties of Mn3Pd20P6 and Mn3Ni20P6 were studied by magnetization measurements. For Mn3Pd20P6 a transition, suggested to be of first order, to a ferromagnetic structure takes place at 110 K, whereas the saturation magnetization shows unusual temperature dependence. Magnetization vs. field loops show very weak coercivity, and the magnitude of the saturation magnetization agrees well with parallel Mn magnetic moments on two different sublattices of 4.24(8) μB, and 2.88(8) μB, respectively, found by neutron powder diffraction at 10 K. Magnetization vs. temperature measurements for Mn3Ni20P6 do not show a well-defined transition temperature, but show signatures of magnetic order with small excess magnetic moments aligned by the applied field below about 240 K. Further, signatures of a spin reorientation process at around 30 K are noted.