Unusual magnetic and transport properties of heavily disordered Mn–Zn–M (M = Ga and Sn) alloys with a β-Mn-type chiral structure

Abstract

The solid-solution alloys of Mn–Zn–Ga and Mn–Zn–Sn have been synthesized by a high-temperature method and structurally characterized by X-ray diffraction studies. The substitutional solid-solution alloys that crystallize in the chiral space group P4₁32 or P4₃32 adopt the A13-type structure (β-Mn). Similar to β-Mn, the 20 atoms in the cubic unit cell are distributed over 8c and 12d Wyckoff positions. In the structure of β-Mn-type Mn–Zn–Ga (Sn) alloys, the 8c position is occupied by the Mn atom only and remains unaffected by chemical substitution. The 12d site that forms a hyperkagomé network (“distorted windmill”) composed of corner-sharing triangles is randomly occupied by Mn, Zn, and M (M = Ga or Sn) atoms in the alloys of Mn_0.80Zn_0.15Ga_0.05 and Mn_0.80Zn_0.15Sn_0.05. Both of them possess a magnetically frustrated ground state, and the magnetic frustration is attributed to the formation of a distorted network of corner-sharing triangles composed of mixed Mn/Zn/Ga(Sn) sites. The negative temperature coefficient of resistivity in Mn_0.80Zn_0.15Sn_0.05 obeys the Mooij criterion, and the very low mobility of charge carriers can be attributed to the high degree of atomic disorder within the structures.