Substantial magnetoelectric coupling in nanocrystalline-Fe2TeO6 at room temperature

Abstract

Nanocrystalline Fe2TeO6 (FTO) is synthesized following the sol-gel process. The nanoaspect of FTO is confirmed from transmission electron microscopy, where the particles of sizes 10–40 nm are seen. Magnetic measurement on nano-FTO confirms the antiferromagnetic nature of particles having Nèel temperature TN = 167 K, which is very much lower than that of bulk (210 K). Polarization verses electric field loop measurement at room temperature (RT) gives the remanent polarization (Pr) value of 0.098 μC/cm2, confirming ferroelectricity in FTO. A nonmonotonous increase in the remanent polarization is noticed when an external magnetic field is applied on the sample. This is a clear indication of prevailing substantial magnetoelectric (ME) coupling in the sample at room temperature. The quantification of magnetoelectricity is done by directly measuring the ME voltage (V) in the presence of varying dc magnetic field (H), and the ME coefficients are obtained using a quadratic relation in H. The values so obtained for the first order (α/d), second order (β/d), and third order (γ/d) ME coefficients are ∼0.22 mV cm−1Oe−1, ∼−1.70 × 10−2 mV cm−1 Oe−2, and ∼0.72 × 10−6 mV cm−1 Oe−3, respectively. The presence of ferroelectricity and magnetoelectricity above the Nèel temperature is a very unusual phenomenon in this material. The presence of short range magnetic ordering which prevails even up to RT, much higher than that of long range magnetic ordering temperature, is suspected to be responsible for this.