Multiferroic materials and devices have attracted intensified recent interests due to the demonstrated strong magnetoelectric (ME) coupling in new multiferroic materials and devices with unique functionalities and superior performance characteristics. Strong ME coupling has been demonstrated in a variety of multiferroic heterostructures, including bulk magnetic on ferro/piezoelectric multiferroic heterostructures, magnetic film on ferro/piezoelectric slab multiferroic heterostructures, thin film multiferroic heterostructures, etc. Different multiferroic devices have been demonstrated, which include magnetic sensors, energy harvesters, and voltage tunable multiferroic RF/microwave devices which are compact, lightweight, and power efficient. In this progress report, we cover the most recent progress on multiferroic heterostructures and devices with a focus on voltage tunable multiferroic heterostructures and devices with strong converse ME coupling. Recent progress on magnetic-field tunable RF/microwave dev...

Voltage control of magnetism in multiferroic heterostructures and devices

We have measured electromagnetic energy harvesting properties of all-thin-film magnetoelectric (ME) heterostructures on Si cantilevers. The devices are built on a silicon oxide/nitride/oxide stack, and the ME layers consist of a magnetostrictive Fe0.7Ga0.3 thin film and a Pb(Zr0.52Ti0.48)O3 piezoelectric thin film. The harvested peak power at 1 Oe is 0.7 mW/cm3 (RMS) at the resonant frequency (3.8 kHz) with a load of 12.5 kΩ. The resonant frequency was found to display DC bias magnetic field dependence indicative of a magnetization canting with respect to the cantilever easy axis as a result of interplay between the anisotropy and Zeeman energies.

Energy harvesting properties of all-thin-film multiferroic cantilevers

In this paper, giant resonant magnetoelectric (ME) effect in an unsymmetrical bi-layered Metglas/Pb(Zr,Ti)O3 ME composites with multi-push pull configuration that can be significantly tuned was investigated experimentally and theoretically. The actual measured and predicted results present the similar resonant frequency shifting behaviors for such ME composites: The resonant frequency can be varied from 70 Hz to 220 Hz by tip mass loading, where the ME voltage coefficients were over 250 V/cm-Oe. Moreover, the giant frequency-tunable resonant effect allowed us to design a 60 Hz magnetic field energy harvester to be capable of harvesting energy generated by electronic instruments working on a 60 Hz ac power supply.

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Giant resonant magnetoelectric effect in bi-layered Metglas/Pb(Zr,Ti)O3 composites

Magnetoelectric (ME) cantilever resonators have been successfully employed as magnetic sensors to measure low magnetic fields; however, high relative resolution enabling magnetometry in high magnetic fields is lacking. Here, we present on-chip silicon based ME microelectromechanical (MEMS) doubly clamped resonators which can be utilized as high sensitivity, low power magnetic sensors. The resonator is a fully suspended thin film ME heterostructure composed of an active magnetoelastic layer (Fe0.3Co0.7), which is strain coupled to a piezoelectric signal/excitation layer (AlN). By controlling uniaxial stress arising from the large magnetoelastic properties of magnetostrictive FeCo, a magnetically driven shift of the resonance frequency of the first fundamental flexural mode is observed. The theoretical intrinsic magnetic noise floor of such sensors reaches a minimum value of 35 pT/Hz. This approach shows a magnetic field sensitivity of ∼5 Hz/mT in a bias magnetic field of up to 120 mT. Such sensors have the...

Magnetic field response of doubly clamped magnetoelectric microelectromechanical AlN-FeCo resonators

This paper presents a wide-bandwidth high-sensitivity magnetostrictive/piezoelectric magnetoelectric (ME) composite (PZT-5/Terfenol-D/PZT-8). The resonant frequencies of the ME laminate structure can be adjusted by modulating the bias voltage across PZT-5 layer. Model and methods for the resonant ME effects in laminate composites under adjustable bias voltages are presented. The relationships between the control voltage, the strain, the Young's modulus, the first-order resonant frequencies and the resonant ME coefficient are analyzed. Theoretical analyses show that the first-order resonant frequencies of the laminate structure are almost a linear function of the applied dc bias voltage at a small strain. The ME coefficient is hardly related to the control voltage. The experimental results are in good agreement with the analytical results. For a control voltage of ±170 V, the first-order resonant frequencies can be linearly adjusted. The adjusted maximum of the resonant frequency is 1 kHz. The ratio of the adjusted value to the bias control voltage is 2.94 Hz/V. For the larger control voltage (such as ±350 V), the wider adjusted resonant frequency (over 2 kHz or 1.73%) can be obtained. Thus, the ME composite with a high sensitivity and a wide frequency bandwidth can be used in ME transducer and energy harvesting.

Wide-bandwidth high-sensitivity magnetoelectric effect of magnetostrictive/piezoelectric composites under adjustable bias voltage

We report on a giant tunable enhanced resonant magnetoelectric (ME) coupling in multiferroic magnetostrictive/piezoelectric composite bimorph structures. The approach uses a magnetic/electric field assisted stress-reconfigurable resonance to produce frequency tuning of up to 100%. The studies were performed by laser Doppler spectroscopy. We also show that this principle of a continuously tuned resonance might be used to improve sensitivity for ME magnetic sensors.

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K. Bussman

Papers

Enhanced resonant magnetoelectric coupling in frequency-tunable composite multiferroic bimorph structures