Magnetic and Structural Studies of G-Phase Compound Mn₆Ni₁₆Si₇

Transition metal compounds with complex crystal structures tend to demonstrate interesting magnetic coupling resulting in unusual magnetic properties. In this work, the structural and magnetic characterization of a single crystal of the Ni-Mn-Si based G-phase compound, Mn₆Ni₁₆Si₇, grown by the Czochralski method, is reported. In this structure, isolated octahedral Mn₆ clusters form an fcc lattice. As each octahedron consists of eight edge-sharing equilateral triangles, the possibility for geometric frustration exists. Magnetization and specific heat measurements showed two magnetic phase transitions at 197 and 50 K, respectively. At 100 K neutron diffraction on powder samples shows a magnetic structure with k = (001) in which only four of the six Mn spins per cluster order along ⟨100⟩ directions giving a two-dimensional magnetic structure consistent with intracluster frustration. Below the 50 K phase transition, the Mn spin-cants away from ⟨100⟩ directions, and a weak moment develops on the two remaining Mn octahedral sites.