Room temperature multiferroic behavior and magnetoelectric coupling in (K,Na)NbO3-based ceramics

Polycrystalline (K0.48Na0.52)0.95Li0.05(Nb0.95Sb0.05)1-xFexO3 (0 ≤ x ≤ 0.030) ceramics are synthesized by the conventional solid state reaction method. The samples with 0.010 ≤ x ≤ 0.030 are found to possess good ferroelectricity, weak ferromagnetism and large magnetodielectric effect simultaneously at room temperature. Temperature dependence of magnetization and dielectric properties show that there are both magnetic and magnetodielectric anomalies in the vicinity of the ferroelectric rhombohedral-orthorhombic (TR-O) and orthorhombic-tetragonal (TO-T) phase transition temperatures. Furthermore, magnetodielectric effect as large as 16% is observed at 0.9 T near TR-O when x = 0.030. According to these results, a strong spin-lattice coupling is considered to exist in these samples. In the structure transition process, the spin interactions between Fe ions will alter for the severe distortion of the FeO6 octahedron. Moreover, since there are more possible polarization vectors due to polymorphic phase transition (PPT), the local polarization of FeO6 will also be greatly affected when the external magnetic field changes the spin interactions.