Europium $c$-axis ferromagnetism in Eu(Co$_{1-x}$Ni$_{x}$)$_{2-y}$As$_{2}$: A single-crystal neutron diffraction study

Tianxiong Han; Santanu Pakhira; N. S. Sangeetha; S. X. M. Riberolles; T. W. Heitmann; Yan Wu; D. C. Johnston; R. J. McQueeney; B. G. Ueland

doi:10.1103/PhysRevB.109.174428

paper

Europium $c$ -axis ferromagnetism in Eu(Co $_{1 - x}$ Ni $_{x}$ ) $_{2 - y}$ As $_{2}$ : A single-crystal neutron diffraction study

arXiv:2402.06773 · doi:10.1103/PhysRevB.109.174428

Abstract

We report neutron diffraction results for the body-centered-tetragonal series Eu(Co $_{1 - x}$ Ni $_{x}$ ) $_{2 - y}$ As $_{2}$ , $x = 0.10$ , $0.20$ , $0.42$ , and $0.82$ , $y \leq 0.10$ , that detail changes to the magnetic ordering with nominal hole doping. We report the antiferromagnetic (AFM) propagation vectors, magnetic transition temperatures, and the ordered magnetic moments. We find a nonmonotonic change of the AFM propagation vector with $x$ , with a minimum occurring at the tetragonal to collapsed-tetragonal phase crossover. For $x = 0.10$ and $0.82$ we find $c$ -axis helix ordering of the Eu magnetic moments (spins) similar to $x = 0$ and $1$ , with the spins oriented within the $ab$ -plane. For $x = 0.20$ and $0.42$ we find higher-temperature $c$ -axis FM order and lower-temperature $c$ -axis cone order. Using the extinction conditions for the space group, we discovered that the Eu spins are ordered in the higher-temperature $c$ -axis FM phase for intermediate values of $x$ , contrary to a previous report suggesting only Co/Ni spin ordering. Although we cannot directly confirm that the Co/Ni spins are also ordered, we suggest that $c$ -axis itinerant-FM ordering of the Co/Ni spins could provide a molecular field that drives FM ordering of the Eu spins, which in turn provides the anisotropy for the lower-temperature $c$ -axis cone order.

Europium c-axis ferromagnetism in Eu(Co1−x​Nix​)2−y​As2​: A single-crystal neutron diffraction study

Abstract

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Europium $c$ -axis ferromagnetism in Eu(Co $_{1 - x}$ Ni $_{x}$ ) $_{2 - y}$ As $_{2}$ : A single-crystal neutron diffraction study