Contrasting magnetic and magnetoelectric properties of LuM W O6 (M=Fe and Cr): Role of spin frustration and noncollinear magnetic structure

We report the magnetic and magnetoelectric properties of two isostructural polar compounds LuMWO6(M=Fe and Cr) that were synthesized at high pressure and high temperatures. Both compounds have a polar orthorhombic aeschynite-type structure (space group Pna21) with the ordered M3+ and W6+ ions. Magnetization measurements show that the Fe3+ spins in LuFeWO6 and Cr3+ spins in LuCrWO6 exhibit antiferromagnetic (AFM) ordering at TN=11.8 and 19.2 K, respectively. Powder neutron diffraction analysis at 1.5 K reveals that LuFeWO6 has a noncollinear AFM structure with k = (0, 12,12), whereas LuCrWO6 has a collinear AFM arrangement with k = (0, 0, 0). The noncollinear AFM structure in LuFeWO6 causes an additional electric polarization, whereas the collinear magnetic order in LuCrWO6 does not. Our density functional theory calculations indicate that LuFeWO6 exhibits spin frustration, which is absent in LuCrWO6. This finding suggests that the induced electric polarization at TN in LuFeWO6 occurs due to a noncollinear spin structure resulting from magnetic frustration.