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Powder X-ray and neutron diffraction has been used to determine the crystal and magnetic structure of Mn3Ni20P6. The crystal structure is cubic Fm3m (no. 225), with the unit cell parameter a = 11.0820(2) Ĺ. Mn3Ni20P6 is isostructural with the ferromagnetic compound Mn3Pd20P6 , which previously has been reported (1). The behaviour of the magnetization of Mn3Ni20P6 is complex; there is no significant characteristic in the magnetization vs. temperature curves that even allows a rough estimate of an ordering temperature.
The neutron diffraction profiles show a commensurate magnetic ordering between 26 K and 29 K, with a propagation vector along (0 0 ½). Below 26 K, the magnetic structure is incommensurate, with a slightly different propagation vector.
A solid solution of Mn3(Pd1-xNix)20P6 (x < 0.20) have been found. These solid solutions order ferromagnetically and the Curie temperature is lowered with increasing Ni content. Detailed results regarding the magnetic structures from neutron diffraction experiments will be presented.
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