Jie Fang Li

Modeling and detection of quasi-static nanotesla magnetic field variations using magnetoelectric laminate sensors

Laminated composites of magnetostrictive and piezoelectric layers have been developed for their magnetoelectric (ME) product tensor properties. In spite of the considerable progress in materials aspects, little attention has been given to ME laminate incorporation into a detection technology. Here, we present a ME technology including the laminate equivalent model, detection circuitry consideration and noise mitigation for ME laminate sensors operated at quasi-static (≤10 Hz) frequencies. We then constructed a passive magnetic field prototype sensor unit and detected a 2.6 nanotesla magnetic signal at 1 Hz frequency.

A review on equivalent magnetic noise of magnetoelectric laminate sensors

Since the turn of the millennium, multi-phase magnetoelectric (ME) composites have been subject to attention and development, and giant ME effects have been found in laminate composites of piezoelectric and magnetostrictive layers. From an application perspective, the practical usefulness of a magnetic sensor is determined not only by the output signal of the sensor in response to an incident magnetic field, but also by the equivalent magnetic noise generated in the absence of such an incident field. Here, a short review of developments in equivalent magnetic noise reduction for ME sensors is presented. This review focuses on internal noise, the analysis of the noise contributions and a summary of noise reduction strategies. Furthermore, external vibration noise is also discussed. The review concludes with an outlook on future possibilities and scientific challenges in the field of ME magnetic sensors.

Evaluation of Applied Axial Field Modulation Technique on ME Sensor Input Equivalent Magnetic Noise Rejection

By using nonlinearity effects in magnetostrictive -piezoelectric laminated sensors, modulation techniques can transfer low-frequency signals to higher frequencies. Theory predicts that the transfer ability depends mainly on the amplitude of the carrier signal and the sensor nonlinearity. This was confirmed by our experiments. We present the first analysis on a ME noise model associated to a modulation technique. Furthermore, the overall equivalent magnetic noise was analyzed, and shown to be dominated only by the signal transfer ability and the output electrical noise level appearing around the carrier frequency.

Giant magnetoelectric effect in laminate composites

It has been found that laminate composites of longitudinally magnetized magnetostrictive and transversely poled piezoelectric layers (an L–T laminate composite) have a giant magnetoelectric (ME) effect. Relatively high ME coupling, that is significant exchange between magnetization and polarization, is demonstrated.

Ground State Monoclinic (M-b) Phase in (110) BiFeO3 Epitaxial Thin Films

The lattice structure of (110)-oriented BiFeO3 epitaxial thin layers has been identified by synchrotron x-ray diffraction. By using (221) and (221¯) peaks in the (HHL) zone, a ground state monoclinic Mb phase has been observed with lattice parameters of (β;am∕√2andcm)=(89.35°;3.985and3.888A). These results demonstrate a change in phase stability from rhombohedral in bulk single crystals, to monoclinic in epitaxial thin films with two domain states whose polarization is slightly tilted away from [110] towards [111].

Volatile and nonvolatile magnetic easy-axis rotation in epitaxial ferromagnetic thin films on ferroelectric single crystal substrates

We explored the relationship between phase transformation and magnetoelectric effect by depositing epitaxial CoFe2O4 films on ⟨110⟩ oriented Pb(Mg,Nb)O3-PbTiO3 (PMN-PT) with three different PbTiO3 contents (PMN-28PT, PMN-29.5PT, and PMN-30PT). Electric-field controlled rhombohedral to orthorhombic phase transformation was confirmed by both piezoelectric and dielectric constant measurements. A giant in-plane (IP) uniaxial strain in CoFe2O4 film was induced due to dramatic lattice parameter change trigged by phase transition. Magnetic easy axis can be rotated from IP⟨110⟩ to IP⟨001⟩. More importantly, the phase transformation could be either reversible or irreversible, resulting in either volatile or nonvolatile magnetic easy axis rotations.

Giant magnetoelectric effect in nonlinear Metglas/PIN-PMN-PT multiferroic heterostructure

In this paper, we demonstrate high converse magnetoelectric (ME) coupling in a Metglas/Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) laminated ME composite by exploiting stress and field induced reversible ferroelectric-ferroelectric phase transitions in a relaxor ferroelectric single crystal. The approach exploits large transformational strain induced by low applied electric field in a PIN-PMN-PT crystal that was mechanically stressed close to a rhombohedral to orthorhombic phase transformation. The ME coefficient was enhanced by an order of magnitude as compared to the linear piezoelectric regime, with a maximum value of 1.3 × 10−7 s m−1 in non-resonant mode. This phenomenon can thus be exploited to provide improvements in the development of ME devices and magnetic sensors.

Tunable features of magnetoelectric transformers

We have found that magnetostrictive FeBSiC alloy ribbons laminated with piezoelectric Pb(Zr,Ti)O3 fiber can act as a tunable transformer when driven under resonant conditions. These composites were also found to exhibit the strongest resonant magnetoelectric voltage coefficient of 750 V/ cm-Oe. The tunable features were achieved by applying small dc magnetic biases of -5 les Hdc les 5 Oe. The features include 1) a high voltage gain of -55 les Vgain les 55; and 2) a large current-to-voltage conversion of -2000 les alphaI-V les 2000 (V/A). The tunable transformer features can be attributed to large changes in the piezomagnetic coefficient and permeability of the magnetostrictive phase under Hdc.

Solid-state synthesis of perovskite-spinel nanocomposites

Multifunctional materials are of interest due to their potential for numerous device applications. We have developed a synthesis method for novel, magnetoelectric Mn0.5Zn0.5Fe2O4-BaTiO3 two-phase nanocomposites, via substrate-assisted solid-state reaction. The morphologies of the nanocomposites were dependent on substrate orientation. Extra particle facets were found to develop, where phase coexistence was observed by high-resolution electron microscopy in the vicinity of the extra facets, indicating that perovskite and spinel can self-organize with novel phase distributions at the nanoscale. This type of two-phase perovskite-spinel nanostructure offers the potential to engineer new types of multiferroic materials.

Magnetoelectric properties of flexible BiFeO3/Ni tapes

We report ferroelectric (FE), ferromagnetic, and magnetoelectric (ME) properties of BiFeO3 films directly deposited on flexible magnetic Ni tapes. Without use of metal-oxide and/or noble metal buffer layer between the BiFeO3 and the Ni, both ferroelectric and magnetic properties of the film and the substrate are preserved. X-ray diffraction and transmission electron microscopy analyses confirm the formation of preferentially oriented (110) BiFeO3 film on Ni tapes. The BiFeO3 film has a saturation polarization and a piezoelectric d33 coefficient of 69 μC/cm2 and 52 pm/V, respectively. The BiFeO3/Ni tape shows a magnetoelectric coefficient of 3.5 mV/cm·Oe.