Crystal growth and evolution of magnetism in the EuCuP-EuCuAs solid solution

Abstract

The hexagonal Eu⁢𝑀⁢𝑋 (𝑀=Cu, Ag, Au; 𝑋=P, As, Sb, Bi) compounds host interesting electronic and magnetic properties, with seemingly intertwined topology and transport properties. One key feature of such behavior is the nature of the ordered magnetic structure. In EuCuAs, a topological Hall effect is caused by a conical spin structure that emerges when a field is applied within the easy-plane (𝐻 ⊥ 𝑐) of the helical ground state that exists below the Neel temperature of 𝑇𝑁=14K. On the other hand, EuCuP is an easy-axis ferromagnet with a Curie temperature 𝑇𝐶 near 31 K. Here, we investigate the evolution of the magnetic properties in EuCuAs1−𝑥⁢P𝑥 single crystals with 0.16 ≤𝑥≤ 0.75. Crystals grown by cooling slowly in a Sn flux possessed macroscale inhomogeneity of As/P, particularly for arsenic-rich crystals. However, growth in a Sn flux via an isothermal dwell at 600⁢∘⁢C produced crystals that were homogeneous within the resolution of the probes utilized to investigate these crystals. The unit cell volumes, Curie-Weiss temperatures, and magnetic transitions trend linearly with composition and the magnetic anisotropy is reduced in the alloys. The magnetization data of crystals with 𝑥=0.16 and 0.24 indicate an easy-plane antiferromagnetic ground state while behavior similar to ferromagnetism is observed for crystals with 𝑥≥ 0.41. The temperature-dependent magnetization data possess multiple transitions for compositions near EuCuAs0.75⁢P0.25, revealing a competition of ground states in this arsenic-rich region of the phase diagram. Neutron diffraction data for EuCuP are also presented as a follow up to previous results that revealed a two-step transition at 𝑇𝐶; the observed data were consistent with ferromagnetic order at 𝑇=5K.