Physical and magnetic properties of Ba(Fe_(1-x)Mn_x)_2As_2 single crystals

TL;DR

This study investigates the structural, magnetic, and electronic properties of Ba(Fe_(1-x)Mn_x)_2As_2 single crystals, revealing phase separation at higher Mn levels and the absence of superconductivity despite suppression of magnetic transitions.

Contribution

The paper provides detailed phase diagrams and characterization of Mn substitution effects in BaFe_2As_2, highlighting differences from other transition metal dopings and the lack of induced superconductivity.

Findings

Phase separation occurs for x>0.1-0.2.

Superconductivity is not observed at any Mn substitution level.

Pressure effects are non-cumulative with Mn substitution in x=0.102 samples.

Abstract

Single crystals of Ba(Fe_(1-x)Mn_x)_2As_2, 0<x<0.148, have been grown and characterized by structural, magnetic, electrical transport and thermopower measurements. Although growths of single crystals of Ba(Fe_(1-x)Mn_x)_2As_2 for the full 0<=x<=1 range were made, we find evidence for phase separation (associated with some form of immiscibility) starting for x>0.1-0.2. Our measurements show that whereas the structural/magnetic phase transition found in pure BaFe_2As_2 at 134 K is initially suppressed by Mn substitution, superconductivity is not observed at any substitution level. Although the effect of hydrostatic pressure up to 20 kbar in the parent BaFe_2As_2 compound is to suppress the structural/magnetic transition at the approximate rate of 0.9 K/kbar, the effects of pressure and Mn substitution in the x=0.102 compound are not cumulative. Phase diagrams of transition temperature versus substitution concentration, x, based on electrical transport, magnetization and thermopower measurements have been constructed and compared to those of the Ba(Fe_(1-x)TM_x)_2As_2 (TM=Co and Cr) series.