Doping effects of Cr on the physical properties of BaFe$_{1.9-x}$Ni$_{0.1}$Cr$_{x}$As$_{2}$

TL;DR

This study systematically investigates the effects of Cr doping on the structural, magnetic, and electronic properties of BaFe$_{1.9-x}$Ni$_{0.1}$Cr$_{x}$As$_{2}$, revealing persistent antiferromagnetism, structural changes, and carrier localization with doping.

Contribution

It provides new insights into how Cr doping influences magnetism, structure, and charge transport in iron pnictides, showing decoupled tuning of magnetic order and moment.

Findings

Antiferromagnetism persists across all Cr doping levels.

Cr doping alters the FeAs$_4$ tetrahedron and arsenic height.

Charge carriers switch from electron- to hole-type around x=0.5.

Abstract

We present a systematic study on the heavily Cr doped iron pnictides BaFe$_{1.9-x}$Ni$_{0.1}$Cr$_{x}$As$_{2}$ by using elastic neutron scattering, high-resolution synchrotron X-ray diffraction (XRD), resistivity and Hall transport measurements. When the Cr concentration increases from $x=$ 0 to 0.8, neutron diffraction experiments suggest that the collinear antiferromagnetism persists in the whole doping range, where the N\'{e}el temperature $T_N$ coincides with the tetragonal-to-orthorhombic structural transition temperature $T_s$, and both of them keeps around 35 K. The magnetic ordered moment, on the other hand, increases within increasing $x$ until $x=$ 0.5, and then decreases with further increasing $x$. Detailed refinement of the powder XRD patterns reveals that the Cr substitutions actually stretch the FeAs$_4$ tetrahedron along the $c-$axis and lift the arsenic height away Fe-Fe plane. Transport results indicate that the charge carriers become more localized upon Cr doping, then changes from electron-type to hole-type around $x=$ 0.5. Our results suggest that the ordered moment and the ordered temperature of static magnetism in iron pnictides can be decoupled and tuned separately by chemical doping.