Magnetoimpedance modulation in a planar magnetoelectric ferromagnet – piezoelectric heterostructure

Abstract

The effect of a giant change in the impedance of ferromagnetic materials under the action of an external magnetic field is widely used to elaborate highly sensitive magnetic field sensors. The purpose of this work was to demonstrate the possibilities of controlling the magnitude of the magnetoimpedance in a ferromagnet-piezoelectric structure using an electric field. Method. In the measurements, we used a planar heterostructure containing a strip of amorphous ferromagnet Metglas, 25 µm thick and 25 mm long, mechanically connected to a bimorph, 0.5 mm thick and 30 mm long, made of piezoceramic lead zirconate titanate. An alternating current with a frequency of 30 kHz...10 MHz was passed through the strip, the structure was placed in a longitudinal permanent magnetic field of 0...500 Oe, an alternating electric field up to 400 V/cm with a frequency of 60 Hz...50 kHz was applied to the piezobimorph, and the change in the impedance of the strip was recorded. Results. In the absence of electric field, a narrowing of the magnetoimpedance magnetic fields region with a decrease in the current frequency and saturation of the magnetoimpedance in magnetic fields above 334 Oe were observed. The maximum value of the magnetoimpedance reached 18% at a current frequency of 1 MHz. The application of electric field to the piezobimorph led to the appearance of side components in the frequency spectrum of the voltage on the ferromagnetic layer, which indicates the amplitude-phase modulation of the magnetoimpedance. The amplitude modulation coefficient reached a maximum value of 6 · 10−3 for the electric field frequency of 11.2 kHz and decreased monotonically with an increase in the magnetic field. The modulation of the magnetoimpedance occurs due to the converse magnetoelectric effect in the heterostructure, which leads to the modulation of the magnetization of the ferromagnetic layer, and the subsequent change in the relative magnetic permeability and thickness of the skin layer in the ferromagnet. The results obtained can be used to create magnetic fields sensors controlled by an electric field.