Physical and magnetic properties of Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$ single crystals

TL;DR

This study investigates how Ru doping affects the structural, magnetic, and superconducting properties of BaFe$_2$As$_2$, revealing a gradual suppression of magnetic order and a dome-shaped superconducting phase with maximum T$_c$ around x=0.29.

Contribution

It provides the first detailed phase diagram of Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$, showing a more gradual transition compared to other dopants and highlighting the importance of lattice parameter ratios.

Findings

Structural/magnetic transition suppressed with Ru doping.

Superconductivity appears for x>0.2, peaking at T$_c$~16.5 K.

Phase diagram resembles pressure-tuned BaFe$_2$As$_2$.

Abstract

Single crystals of Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$, $x<0.37$, have been grown and characterized by structural, magnetic and transport measurements. These measurements show that the structural/magnetic phase transition found in pure BaFe$_2$As$_2$ at 134 K is suppressed monotonically by Ru doping, but, unlike doping with TM=Co, Ni, Cu, Rh or Pd, the coupled transition seen in the parent compound does not detectably split into two separate ones. Superconductivity is stabilized at low temperatures for $x>0.2$ and continues through the highest doping levels we report. The superconducting region is dome like, with maximum T$_c$ ($\sim16.5$ K) found around $x\sim 0.29$. A phase diagram of temperature versus doping, based on electrical transport and magnetization measurements, has been constructed and compared to those of the Ba(Fe$_{1-x}$TM$_x$)$_2$As$_2$ (TM=Co, Ni, Rh, Pd) series as well as to the temperature-pressure phase diagram for pure BaFe$_2$As$_2$. Suppression of the structural/magnetic phase transition as well as the appearance of superconductivity is much more gradual in Ru doping, as compared to Co, Ni, Rh and Pd doping, and appears to have more in common with BaFe$_2$As$_2$ tuned with pressure; by plotting $T_S/T_m$ and $T_c$ as a function of changes in unit cell dimensions, we find that changed in the $c/a$ ratio, rather than changes in $c$, $a$ or V, unify the $T(p)$ and $T(x)$ phase diagrams for BaFe$_2$As$_2$ and Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$ respectively.