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

The hexagonal EuMX (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-xPx 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 EuCuAs0.75P0.25, 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.