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)O(9), A = Nb or Ta). The exception is Ni4Nb2O9, crystallizing in the orthorhombic Pbcn space group: because of symmetry considerations, its magnetic space group forbids the occurrence of the magnetoelectric effect. Li2Ni2W2O9 crystallizes in the same space group as Ni4Nb2O9; however, as half the Ni2+ cations are replaced by 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-N approximate to 8 K in Li2Ni2W2O9. Through neutron diffraction, the magnetic structure of Li2Ni2W2O9 is solved, and it is confidently established that it presents the Pb'c'n' Shubnikov space group (#60.425), whose point symmetry m'm'm' allows the magnetoelectric effect. This could possibly open the door to a family of magnetoelectric, orthorhombic compounds.