Contrasting magnetic and magnetoelectric properties of LuMWO6(M=Fe and Cr): Role of spin frustration and noncollinear magnetic structure

We report the magnetic and magnetoelectric properties of two isostructural polar compounds $\mathrm{Lu}M\mathrm{W}{\mathrm{O}}₆\phantom{\rule{4pt}{0ex}}(M=\mathrm{Fe}$ and Cr) that were synthesized at high pressure and high temperatures. Both compounds have a polar orthorhombic aeschynite-type structure (space group $Pna{2}₁)$ with the ordered ${M}³⁺$ and ${\mathrm{W}}⁶⁺$ ions. Magnetization measurements show that the ${\mathrm{Fe}}³⁺$ spins in $\mathrm{LuFeW}{\mathrm{O}}₆$ and ${\mathrm{Cr}}³⁺$ spins in $\mathrm{LuCrW}{\mathrm{O}}₆$ exhibit antiferromagnetic (AFM) ordering at ${T}_{\mathrm{N}}=11.8$ and 19.2 K, respectively. Powder neutron diffraction analysis at 1.5 K reveals that $\mathrm{LuFeW}{\mathrm{O}}₆$ has a noncollinear AFM structure with k $=$ (0, $\frac{1}{2},\frac{1}{2})$, whereas $\mathrm{LuCrW}{\mathrm{O}}₆$ has a collinear AFM arrangement with k $=$ (0, 0, 0). The noncollinear AFM structure in $\mathrm{LuFeW}{\mathrm{O}}₆$ causes an additional electric polarization, whereas the collinear magnetic order in $\mathrm{LuCrW}{\mathrm{O}}₆$ does not. Our density functional theory calculations indicate that $\mathrm{LuFeW}{\mathrm{O}}₆$ exhibits spin frustration, which is absent in $\mathrm{LuCrW}{\mathrm{O}}₆$. This finding suggests that the induced electric polarization at ${T}_{\mathrm{N}}$ in $\mathrm{LuFeW}{\mathrm{O}}₆$ occurs due to a noncollinear spin structure resulting from magnetic frustration.