Self-bias response of lead-free (1-x)[0.948 K_0.5Na _0.5NbO₃-0.052 LiSbO₃]-xNi_0.8Zn _0.2Fe₂O₄-nickel magnetoelectric laminate composites

This study reports the magnetoelectric (ME) response of lead-free particulate composites given as (1-x)[0.948 K_0.5Na _0.5NbO₃-0.052 LiSbO₃]-xNi_0.8Zn _0.2Fe₂O₄ (KNNLS-NZF) and bimorph laminates given as KNNLS-NZF/Ni/KNNLS-NZF. The particulate ME composites were found to exhibit island-matrix microstructure as confirmed by scanning electron microscopy and elemental mapping. Detailed investigations were conducted on optimization of the magnitude of magnetic and piezoelectric properties by varying the sintering condition and NZF mole fraction. It was found that longitudinal piezoelectric strain coefficient d₃₃ and electromechanical coupling factor k_p decreased with increasing NZF concentration. On the other hand, the magnitude of saturation magnetization M_s, remnant magnetization M_r, magnetic permeability μ, and magnetostriction λ was found to increase with increasing NZF fraction. The composition 0.7 KNNLS-0.3 NZF sintered at 1060°C was found to exhibit d₃₃ of 73 pC/N, M_s of 19 emu/g, and maximum ME coefficient α_E of 20.14 mV/cm·Oe under H_ac=1 Oe at 1 kHz. The bimorph laminates were fabricated by embedding Ni plate between (1-x)KNNLS-xNZF disks with varying electrical connections to achieve radial and bending modes. The radial mode laminates were found to exhibit typical ME response without any self-bias effect with maximum α_E of 261.3 mV/cm·Oe and high DC magnetic field sensitivity of 1 μT at 1 kHz. The bending mode laminates were found to exhibit self-biased ME response whose magnitude and shape was dependent upon the NZF concentration.