Enhanced strain derivative of Ho substituted cobalt ferrite and improved magnetoelectric coupling in co-sintered bi-layered ME composites

Abstract

The magnetoelectric bilayer composites of Ho substituted cobalt ferrite as piezomagnetic phase and Sr, La modified PZT (PSLZT) as a piezoelectric phase were prepared to study magnetoelectric effect. The Ho substituted cobalt ferrite CoFe2-xHoxO4 where, x = 0.0, 0.01, 0.02, 0.03, 0.05 and 0.15, were successfully synthesized by sol-gel auto combustion method. The phase formation of synthesized Ho substituted cobalt ferrite series has been confirmed by using X-ray diffraction (XRD). For the samples up to x = 0.05 formation of single spinel ferrite phase and for higher concentration i.e. x = 0.15, along with spinel ferrite phase secondary ortho-ferrite phase have been observed. FTIR and Raman spectroscopic analysis has been carried out to confirm the presence of metal oxide functional group at tetrahedral and octahedral sites of spinel structure. Morphological analysis of all the samples under investigation has been carried out using Scanning Electron Microscopy. The magnetostrictive properties were measured at room temperature and the influence of Ho substitution on magnetostrictive properties of cobalt ferrite has also been investigated. Further, the strain derivative (dλ/dH) has been determined in order to understand the piezomagnetic properties of the samples. The strain derivative of Ho substituted cobalt ferrite attains maximum value at a low magnetic field with respect to cobalt ferrite which is useful in stress sensors applications. Finally, the magnetoelectric properties of PSLZT -Ho substituted cobalt ferrite layered composite structure have been investigated. The relation between magnetoelectric properties of the composites and piezomagnetic properties of the ferrite samples has been elucidated based on the theoretical model proposed in the literature by Bichurin et al.