Structure, Magnetism, and the Magnetocaloric Effect of MnFe4Si3 Single Crystals and Powder Samples

Magnetic and structural properties of high quality magnetocaloric MnFe4Si3 single crystals are investigated macroscopically and on an atomic scale. Refinements of combined neutron and X-ray single crystal diffraction data introduce a new structural model in space group P6 characterized by partial ordering of Mn and Fe into layers perpendicular to c on one of the transition metal sites. A second transition metal site is exclusively occupied by iron. MnFe4Si3 has a phase transition to a ferromagnetically ordered phase at approximately 300 K and displays a strong anisotropy of the magnetization and the magnetocaloric effect with the easy axis of magnetization in the a,b-plane. This is confirmed by a refinement of the magnetic structure in the magnetic spacegroup Pm′, which shows that the spins on the sites with mixed occupancy of Mn and Fe are aligned in the a,b-plane. A significant magnetic moment for the site exclusively occupied by iron could not be refined. The thermal evolution of the lattice parameters...