Magnetic and structural studies of G-phase compound Mn$_6$Ni$_{16}$Si$_7$

TL;DR

This study investigates the magnetic and structural properties of the complex G-phase compound Mn$_6$Ni$_{16}$Si$_7$, revealing multiple magnetic phase transitions and geometric frustration effects through comprehensive experimental techniques.

Contribution

It provides the first detailed structural and magnetic characterization of Mn$_6$Ni$_{16}$Si$_7$, highlighting its geometric frustration and complex magnetic ordering.

Findings

Two magnetic phase transitions at 197 K and 50 K.

Magnetic structure with partial Mn spin ordering and frustration.

Development of weak moments below 50 K.

Abstract

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, Mn$_6$Ni$_{16}$Si$_7$, grown by the Czochralski method, is reported. In this structure isolated octahedral Mn$_6$ clusters form a f.c.c. 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 K 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 intra-cluster frustration. Below the 50 K phase transition the Mn spins cant away from $<100>$ directions and a weak moment develops on the two remaining Mn octahedral sites.