A neutron scattering study of the interplay between structure and magnetism in Ba(Fe$_{1-x}$Co$_{x}$)$_2$As$_2$

TL;DR

This study uses neutron diffraction to explore how doping affects the structural and magnetic phases of Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, revealing the suppression of antiferromagnetism and its coupling with lattice structure.

Contribution

It provides detailed phase diagrams and demonstrates the strong coupling between magnetism and lattice structure in electron-doped BaFe$_2$As$_2$.

Findings

Antiferromagnetic order disappears at x ≈ 0.055.

Coexistence of antiferromagnetism and superconductivity observed.

Strong coupling between magnetic order and crystal lattice confirmed.

Abstract

Single crystal neutron diffraction is used to investigate the magnetic and structural phase diagram of the electron doped superconductor Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$. Heat capacity and resistivity measurements have demonstrated that Co doping this system splits the combined antiferromagnetic and structural transition present in BaFe$_2$As$_2$ into two distinct transitions. For $x$=0.025, we find that the upper transition is between the high-temperature tetragonal and low-temperature orthorhombic structures with ($T_{\mathrm{TO}}=99 \pm 0.5$ K) and the antiferromagnetic transition occurs at $T_{\mathrm{AF}}=93 \pm 0.5$ K. We find that doping rapidly suppresses the antiferromagnetism, with antiferromagnetic order disappearing at $x \approx 0.055$. However, there is a region of co-existence of antiferromagnetism and superconductivity. The effect of the antiferromagnetic transition can be seen in the temperature dependence of the structural Bragg peaks from both neutron scattering and x-ray diffraction. We infer from this that there is strong coupling between the antiferromagnetism and the crystal lattice.