In this study, magnetostrictive powders of CoFe₂O₄ (CFO) and Zn-substituted CoFe₂O₄ (CZFO, Zn = 0.1, 0.2) were synthesized in order to decrease the optimal dc magnetic field (Hopt.), which is required to obtain a reliable magnetoelectric (ME) voltage in a 3-0 type particulate composite system. The CFO powders were prepared as a reference via a typical solid solution process. In particular, two types of heterogeneous CZFO powders were prepared via a stepwise solid solution process. Porous-CFO and dense-CFO powders were synthesized by calcination in a box furnace without and with pelletizing, respectively. Then, heterogeneous structures of pCZFO and dCZFO powders were prepared by Zn-substitution on calcined powders of porous-CFO and dense-CFO, respectively. Compared to the CFO powders, the heterogeneous pCZFO and dCZFO powders exhibited maximal magnetic susceptibilities (χmax) at lower Hdc values below ±50 Oe and ±10 Oe, respectively. The Zn substitution effect on the Hdc shift was more dominant in dCZFO than in pCZFO. This might be because the Zn ion could not diffuse into the dense-CFO powder, resulting in a more heterogeneous structure inducing an effective exchange-spring effect. As a result, ME composites consisting of 0.948Na0.5K0.5NbO₃⁻0.052LiSbO₃ (NKNLS) with CFO, pCZFO, and dCZFO were found to exhibit Hopt. = 966 Oe (NKNLS-CFO), Hopt. = 689⁻828 Oe (NKNLS-pCZFO), and Hopt. = 458⁻481 Oe (NKNLS-dCZFO), respectively. The low values of Hopt. below 500 Oe indicate that the structure of magnetostrictive materials should be considered in order to obtain a minimal Hopt. for high feasibility of ME composites.
Keywords: CZFO; NKNLS; hysteretic magnetization; magnetoelectric voltage; magnetostrictive powders; optimal dc magnetic field; particulate composites; structural effect.