Application Cases

Experiment Name: Magnetoelectric Properties and High-Frequency Resonant Response of Composite Materials

Research Direction: Materials Testing

Test Objective:
Multiferroic magnetoelectric composites have attracted sustained attention due to their potential applications in magnetic field sensing, energy harvesting, and other fields. Magnetoelectric composites consist of a magnetostrictive phase and a piezoelectric phase. Stress-strain transfer occurs through the interface between the two phases. Applying an alternating magnetic field to the material induces vibration. This vibration, transferred to the piezoelectric phase, generates electric polarization, leading to a magnetoelectric response. Through the selection of the two-phase materials and the optimization of the vibration mode, the magnetoelectric coupling coefficient of the composite has been significantly improved. In particular, the shear magnetoelectric coefficient has recently garnered widespread interest due to its promising application prospects in high-frequency magnetic field detection, where a high signal-to-noise ratio can be achieved. Previous work has used magnetostrictive materials such as Terfenol-D and Yttrium Iron Garnet (YIG) to provide longitudinal or shear stress, driving materials with large shear piezoelectric coefficients (e.g., lead magnesium niobate, langasite, polyvinylidene fluoride) to achieve shear strain, thereby fabricating longitudinal-shear or shear-shear vibration mode magnetoelectric composites. As a lead-free piezoelectric material with a high mechanical quality factor (Qm) and low dielectric constant (ε), lithium niobate single crystal possesses large shear piezoelectric coefficients (d15 and d24), indicating the potential for achieving a significant shear magnetoelectric response. Furthermore, lithium niobate can exhibit different piezoelectric coefficients depending on the crystal cut, which is beneficial for designing anisotropic shear vibration mode magnetoelectric devices. Therefore, studying the shear magnetoelectric coefficient using different crystal cuts of lithium niobate single crystal holds both theoretical and practical significance.

Testing Equipment: Mechanical clamping device, ATA-4014 high-voltage power amplifier, impedance spectrum analyzer, lithium niobate single crystal material, epoxy resin or ethyl cyanoacrylate, Teflon tape.

Figure: Schematic Diagram of the Longitudinal-Shear Mode Magnetoelectric Composite Structure

Experimental Procedure:
Metglas sheets (dimensions: 16 mm × 5 mm × 25 µm), in quantities of 3, 5, and 10, were respectively bonded with epoxy resin to form Metglas laminates, thereby increasing their thickness and magnetostrictive stress. A Metglas/LiNbO₃/Metglas laminated composite was prepared using a lithium niobate single crystal (dimensions: 13 mm × 5 mm × 0.5 mm). The mechanical clamping glass in the longitudinal-shear structure was bonded using epoxy resin or ethyl cyanoacrylate to fabricate the laminated magnetoelectric composite. Different single crystal cuts of lithium niobate with various piezoelectric coefficients (d15 or d16), such as xzt/0°, xzt/30°, xyt/0°, xyt/30°, and xyt/41°, were used. Subsequently, the shear piezoelectric coefficient of lithium niobate was measured using a quasi-static d33/d31(+d15) meter. The capacitance and impedance spectrum of lithium niobate were measured using an impedance spectrum analyzer to calculate the dielectric constant. Then, magnetostrictive strips (dimensions: 12 mm × 5 mm × 1 mm) were placed on one side or both sides (one strip on each side) of the longitudinal-shear structure magnetoelectric composite and fixed in position with Teflon tape. The magnetoelectric coefficient of the composite structure was measured at 1 kHz using a self-built testing system in the laboratory. The variation of the magnetoelectric response with frequency (from 1 kHz to 1 MHz) was tested using the ATA-4014 power amplifier.

Experimental Results:
The figure shows the magnetoelectric coefficient (αE15) of Metglas/LiNbO₃ (xzt/0°) longitudinal-shear composite structures with different numbers of bonded Metglas layers, using either epoxy resin or ethyl cyanoacrylate for bonding the mechanical clamping glass. The corresponding shear magnetoelectric coefficient values are indicated in the figure. The formula for calculating the shear magnetoelectric coefficient is αE15 = αE-Clamping − αE-Freedom, where αE-Clamping is the longitudinal + shear magnetoelectric coefficient measured under mechanical clamping, and αE-Freedom is the longitudinal magnetoelectric coefficient measured under mechanical free conditions. The figure shows that the optimal DC bias magnetic field (Hdc) increases with the number of Metglas layers. This is because a thicker magnetostrictive layer requires a larger DC bias magnetic field. Even with 10 bonded Metglas layers, the required DC bias magnetic field remains below 100 Oe (1 Oe = 79.5775 A/m). This is advantageous because Metglas has a higher magnetic permeability in the in-plane direction compared to the traditional magnetostrictive material Terfenol-D. With 5 bonded Metglas layers, the product of the magnetic layer thickness and the piezomagnetic coefficient reaches an optimum, resulting in the maximum magnetoelectric coefficient for the composite. When the adhesive for the mechanical clamping glass was changed to epoxy resin, the shear magnetoelectric coefficient increased from 82 mV/(cm·Oe) to 109 mV/(cm·Oe). Moreover, changing the adhesive improved the shear magnetoelectric coefficient for composites with different numbers of Metglas layers. This is because epoxy resin has a higher elastic modulus than ethyl cyanoacrylate, providing better constraint on the lateral vibration of the Metglas layers, thereby channeling more vibration energy into the piezoelectric phase. To confirm the correspondence between the shear magnetoelectric coefficient and the piezoelectric coefficient, the shear piezoelectric coefficient (d15) of the lithium niobate single crystal was measured using a quasi-static d33/d31(+d15) meter. The results showed that the measured shear piezoelectric coefficient agreed well with the theoretical value. The maximum d15 for the xzt/30° cut of lithium niobate was 77 pC/N. The measured value was slightly lower than the theoretical value, similar to the situation for the standard xzt cut (measured 66 pC/N vs. theoretical 74 pC/N). To study the relationship between crystal orientation and dielectric constant, the capacitance of lithium niobate was tested using an impedance spectrum analyzer. The relationship between capacitance (Cp) and frequency (f) for the 13 mm × 5 mm × 0.5 mm lithium niobate wafer was studied. The capacitance values for both xyt and xzt series cuts at a frequency of 1 kHz were approximately 90 pF. The calculated corresponding dielectric constant (εT11) was 80, which is consistent with theoretical results.

Figure: Relationship between the magnetoelectric coefficient (αE15) of longitudinal-shear composite structures with different numbers of bonded Metglas layers and the DC bias magnetic field

Figure: Specifications of the ATA-4014C High-Voltage Power Amplifier