Magnetic properties, magnetic structure, and possible magnetoelectric effect in orthorhombic corundumlike Li2Ni2W2O9

The magnetoelectric effect is an appealing property displayed by most compounds in the corundum-derived 429 series (${M}₄{A}₂{\mathrm{O}}₉, A=\mathrm{Nb}$ or Ta). The exception is ${\mathrm{Ni}}₄{\mathrm{Nb}}₂{\mathrm{O}}₉$, crystallizing in the orthorhombic Pbcn space group: because of symmetry considerations, its magnetic space group forbids the occurrence of the magnetoelectric effect. ${\mathrm{Li}}₂{\mathrm{Ni}}₂{\mathrm{W}}₂{\mathrm{O}}₉$ crystallizes in the same space group as ${\mathrm{Ni}}₄{\mathrm{Nb}}₂{\mathrm{O}}₉$; however, as half the ${\mathrm{Ni}}²⁺$ cations are replaced by ${\mathrm{Li}}⁺$ cations, the interactions between the remaining magnetic elements are drastically modified. In this paper, we present the results of magnetic bulk measurements, showing an antiferromagnetic ordering coupled with strong ferromagnetic interactions below ${T}_{\mathrm{N}}\ensuremath{\approx}\phantom{\rule{0.16em}{0ex}}8\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ in ${\mathrm{Li}}₂{\mathrm{Ni}}₂{\mathrm{W}}₂{\mathrm{O}}₉$. Through neutron diffraction, the magnetic structure of ${\mathrm{Li}}₂{\mathrm{Ni}}₂{\mathrm{W}}₂{\mathrm{O}}₉$ is solved, and it is confidently established that it presents the ${Pb}^{\ensuremath{'}}{c}^{\ensuremath{'}}{n}^{\ensuremath{'}}$ Shubnikov space group (#60.425), whose point symmetry ${m}^{\ensuremath{'}}{m}^{\ensuremath{'}}{m}^{\ensuremath{'}}$ allows the magnetoelectric effect. This could possibly open the door to a family of magnetoelectric, orthorhombic compounds.