Probing magnetic symmetry in antiferromagnetic Fe4Nb2O9 single crystals by linear magnetoelectric tensor

In the present study, we investigated magnetodielectric, magnetoelectric (ME), and angular-dependent polarization in single-crystal ${\mathrm{Fe}}_{4}{\mathrm{Nb}}_{2}{\mathrm{O}}_{9}$. The magnetodielectric effects in ${\ensuremath{\varepsilon}}_{x}$ ($x//[100]$), ${\ensuremath{\varepsilon}}_{y}$ ($y//[120]$), and ${\ensuremath{\varepsilon}}_{z}$ ($z//[001]$) are found to be significant only around ${T}_{\mathrm{N}}\ensuremath{\approx}95\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ when magnetic fields are applied along three orthogonal x-, y- ($y//[120]$), and $z$ directions. The finite polarization ${P}_{x}, {P}_{y}$, and ${P}_{z}$ of 70, 100, and $30\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{C}/{\mathrm{m}}^{2}$, respectively, can be induced in the antiferromagnetic phase when a finite magnetic field up to 9 T is applied along the three orthogonal directions. The angular-dependent polarization measurements verify the dominating linear ME effects below ${T}_{\mathrm{N}}$. From the above experimental results, a linear ME tensor ${a}_{ij}$ with all nine nonzero components can be inferred, demonstrating a much lower magnetic point group of $\ensuremath{-}{\mathbf{1}}^{\ensuremath{'}}$ for the canted antiferromagnetic configuration.