Demagnetization Effect on the Magnetoelectric Response of Composite Multiferroic Cylinders

Strain-mediated multiferroic composite structures are gaining scientific and technological attention because of the promise of low power consumption and greater flexibility in material and geometry choices. In this study, the direct magnetoelectric coupling coefficient (DME) of composite multiferroic cylinders, consisting of two mechanically bonded concentric cylinders, was analytically modeled under the influence of a radially emanating magnetic field. The analysis framework emphasized the effect of demagnetization on the overall performance. The demagnetization effect was thoroughly considered as a function of the imposed mechanical boundary conditions, the geometrical dimensions of the composite cylinder, and the introduction of a thin elastic layer at the interface between the inner piezomagnetic and outer piezoelectric cylinders. The results indicate that the demagnetization effect adversely impacted the DME coefficient. In a trial to compensate for the reduction in peak DME coefficient due to demagnetization, a non-dimensional geometrical analysis was carried out to identify the geometrical attributes corresponding to the maximum DME. It was observed that the peak DME coefficient was nearly unaffected by varying the inner radius of the composite cylinder, while it approached its maximum value when the thickness of the piezoelectric cylinder was almost 60% of the total thickness of the composite cylinder. The latter conclusion was true for all of the considered boundary conditions.

Long-Term Converse Magnetoelectric Response of Actuated 1-3 Multiferroic Composite Structures

Multiferroic composite materials operating under the principle of strain mediation across the interfaces separating different material boundaries address many limitations of single-phase magnetoelectric materials. Although significant research has been conducted to explore their responses relating to the topography and directionality of material polarization and magnetic loading, there remain unanswered questions regarding the long-term performance of these multiferroic structures. In this study, a multiferroic composite structure consisting of an inner Terfenol-D magnetostrictive cylinder and an outer lead zirconate titanate (PZT) piezoelectric cylinder was investigated. The composite was loaded over a 45-day period with an AC electric field (20 kV/m) at a near-resonant frequency (32.5 kHz) and a simultaneously applied DC magnetic field of 500 Oe. The long-term magnetoelectric and thermal responses were continuously monitored, and an extensive micrographic analysis of pretest and post-test states was performed using scanning electron microscopy (SEM). The extended characterization revealed a significant degradation of ≈30–50% of the magnetoelectric response, whereas SEM micrographs indicated a reduction in the bonding interface quality. The increase in temperature at the onset of loading was associated with the induced oscillatory piezoelectric strain and accounted for 28% of the strain energy loss over nearly one hour.