We report the tunable magnetic structures in the helimagnet $\mathrm{YBa}{\left(\mathrm{C}{\mathrm{u}}_{1-x}\mathrm{F}{\mathrm{e}}_x\right)}_2{\mathrm{O}}_5$ by changing various Cu/Fe ratios. The magnetic properties and structures of the samples were studied by using neutron- and x-ray powder diffraction and susceptibility measurements. The parent material $\mathrm{YBaCuFe}{\mathrm{O}}_5$ (YBCFO) exhibits two antiferromagnetic (AFM) transitions at $T_{N1}\sim 450$ K and $T_{N2}\sim 175$ K. At $T_{N1}$, YBCFO shows a commensurate (CM) spin ordering with a q-wave vector ${\mathit{k}}_{\mathit{c}\mathbf{1}}=(1/21/21/2)$, which transfers to a spiral magnetic ordering at $T_{N2}$ with an incommensurate $q$-wave vector (1/2 1/2 1/2 ±δ), δ  being the incommensurability. Using neutron powder diffraction for samples with $0.490\le x\le 0.505, T_{N2}$ was observed to systematically increase from 125 to 236 K as a function of the Cu/Fe ratio. For $x=0.510$ and 0.515, additional magnetic reflections with a propagation vector ${\mathit{k}}_{\mathit{c}\mathbf{2}}=(1/21/20)$ appear below $T_{N3}\sim 245$ and 269 K, respectively. This CM phase shows a collinear magnetic ordering. These transition temperatures are consistent with the AFM transitions of the magnetization data. Experiments were also conducted to synthesize the samples with different thermal treatments, demonstrating the $T_{N2}$ and $T_{N3}$ to be sensitive to the annealing conditions. These results can be understood within the framework of the random distributions of the dopants (impurities) at the $B$ site of a double-perovskite lattice and demonstrate that the magnetic ordering in the helimagnet YBCFO can be systematically tuned by changing the Cu/Fe ratio.

• Received 30 October 2023
• Accepted 12 April 2024

DOI:https://doi.org/10.1103/PhysRevMaterials.8.054404