Ba₃NbFe₃Si₂O₁₄: A New Multiferroic with a 2D Triangular Fe³⁺ Motif

Single crystals of the new multiferroic Ba 3 NbFe 3 Si 2 O 14 have been synthesized and characterized via X-ray diffraction, magnetic susceptibility, NMR, and electric polarization measurements. The underlying topology of the Fe 3+ spins is composed of isolated triangular units stacked in 2D layers along the c -direction of the trigonal lattice. Magnetic susceptibility experiments verify the spin state of the iron moments ( S = 5/2), and large antiferromagnetic interactions with θ = −190 K. A cusp in the susceptibility and lambda-like feature in the specific heat indicate a magnetic phase transition at T N = 26 K, resulting in a frustration index of f = 7. A significant amount of spin entropy is released at higher temperatures, suggestive of short-ranged magnetic correlations developing at 50 K (as evidenced by features in the specific heat and thermal conductivity). The development of a spontaneous electric polarization below 26 K verifies that Ba 3 NbFe 3 Si 2 O 14 is a multiferroic.