Tunable magnetism and structural transformations in mixed light- and heavy-lanthanide dialuminides

Abstract

Rare-earth intermetallics play a critical yet often obscure role in numerous technological applications, including sensors, actuators, permanent magnets, and rechargeable batteries; therefore, understanding their basic science is of utmost importance. Here we report structural behaviors, specific heat, and magnetism of $\mathrm{P}{\mathrm{r}}_{1\text{--}x}\mathrm{E}{\mathrm{r}}_{x}\mathrm{A}{\mathrm{l}}_{2}$ studied by means of temperature-dependent x-ray powder diffraction, heat capacity, and magnetization measurements, in addition to first-principles calculations. Although the cubic lattice of $\mathrm{PrA}{\mathrm{l}}_{2}$ distorts tetragonally at the Curie temperature ${T}_{C}$, the distortion is rhombohedral in $\mathrm{ErA}{\mathrm{l}}_{2}$, creating a potential for instability in the pseudobinary $\mathrm{PrA}{\mathrm{l}}_{2}\text{\ensuremath{-}}\mathrm{ErA}{\mathrm{l}}_{2}$ system. When $0.05\ensuremath{\le}x\ensuremath{\le}0.5$, materials show complex magnetization behaviors, including metamagnetic transitions and Griffith-like phase. Unique among other mixed-lanthanide dialuminides, the substitution of Er for Pr in $\mathrm{P}{\mathrm{r}}_{1\text{--}x}\mathrm{E}{\mathrm{r}}_{x}\mathrm{A}{\mathrm{l}}_{2}$ results in unexpected ferrimagnetic behavior, and the ferrimagnetic interactions become strongest around $x=0.25$, where the compound shows unusual metamagnetic like transitions observed only in the odd-numbered quadrants of the full magnetic field cycles. The electronic structure calculations, including exchange interactions and crystal field splitting, magnetic moments, anisotropic $4f$ energy density, and magnetic surface potentials rationalize the interesting physics observed experimentally.