One of the new materials that have recently attracted wide attention of researchers are magnetoelectric (ME) composites. Great interest in these materials is due to their properties associated with the transformation of electric polarization/magnetization under the influence of external magnetic/electric fields and the possibility of their use to create new devices. In the proposed review, ME magnetic field sensors based on the widely used structures Terfenol—PZT/PMN-PT, Metglas—PZT/PMN-PT, and Metglas—Lithium niobate, among others, are considered as the first applications of the ME effect in technology. Estimates of the parameters of ME sensors are given, and comparative characteristics of magnetic field sensors are presented. Taking into account the high sensitivity of ME magnetic field sensors, comparable to superconducting quantum interference devices (SQUIDs), we discuss the areas of their application.

Non-contact mapping of magnetic fields produced by the human heart muscle requires the application of arrays of miniature and highly sensitive magnetic field sensors. In this article, we describe a MEMS technology of laminated magnetoelectric heterostructures comprising a thin piezoelectric lithium niobate single crystal and a film of magnetostrictive metglas. In the former, a ferroelectric bidomain structure is created using a technique developed by the authors. A cantilever is formed by microblasting inside the lithium niobate crystal. Metglas layers are deposited by magnetron sputtering. The quality of the metglas layers was assessed by XPS depth profiling and TEM. Detailed measurements of the magnetoelectric effect in the quasistatic and dynamic modes were performed. The magnetoelectric coefficient |α₃₂| reaches a value of 492 V/(cm·Oe) at bending resonance. The quality factor of the structure was Q = 520. The average phase amounted to 93.4° ± 2.7° for the magnetic field amplitude ranging from 12 to 100 pT. An AC magnetic field detection limit of 12 pT at a resonance frequency of 3065 Hz was achieved which exceeds by a factor of 5 the best value for magnetoelectric MEMS lead-free composites reported in the literature. The noise level of the magnetoelectric signal was 0.47 µV/Hz^1/2. Ways to improve the sensitivity of the developed sensors to the magnetic field for biomedical applications are indicated.

This paper investigates the possibilities of creating magnetic field sensors using the direct magnetoelectric (ME) effect in a monolithic heterostructure of amorphous ferromagnetic material/langatate. Layers of 1.5 μm-thick FeCoSiB amorphous ferromagnetic material were deposited on the surface of the langatate single crystal using magnetron sputtering. At the resonance frequency of the structure, 107 kHz, the ME coefficient of linear conversion of 76.6 V/(Oe∙cm) was obtained. Furthermore, the nonlinear ME effect of voltage harmonic generation was observed with an increasing excitation magnetic field. The efficiency of generating the second and third harmonics was about 6.3 V/(Oe²∙cm) and 1.8 V/(Oe³∙cm), respectively. A hysteresis dependence of ME voltage on a permanent magnetic field was observed due to the presence of α-Fe iron crystalline phases in the magnetic layer. At the resonance frequency, the monolithic heterostructure had a sensitivity to the AC magnetic field of 4.6 V/Oe, a minimum detectable magnetic field of ~70 pT, and a low level of magnetic noise of 0.36 pT/Hz^1/2, which allows it to be used in ME magnetic field sensors.

The effect of annealing in a permanent magnetic field on the magnitude of magnetoelectric coefficient in three-layered gradient magnetoelectric LiNbO₃/Ni/Metglas composites has been studied. A method of electrochemical nickel deposition on bidomain lithium niobate crystals has been demonstrated. We show that the optimum annealing temperature in a permanent magnetic field for the generation of the highest remanence in the Ni layer is 350 °C. The specimens annealed at this temperature exhibit the greatest shift of the magnetoelectric coefficient dependence on external magnetic field magnitude relative to the value H_dc = 0. The quasi-static magnetoelectric coefficient in the absence of an external magnetic field proves to be 1.2 V/(cm ∙ Oe). The highest magnetoelectric coefficient that has been achieved at a bending structure resonance frequency of 278 Hz proves to be 199.3 V/(cm ∙ Oe) without application of an external magnetic field. The experimental magnetoelectric coefficient figures for three-layered gradient LiNbO₃/Ni/Metglas composites are not inferior to those for most magnetoelectric composite materials reported earlier.

Magnetoelectric (ME) composites have a wide range of possible applications, especially as room-temperature sensors of weak magnetic fields in magnetocardiography and magnetoencephalography medical diagnostic equipment. In most works on ME composites, structures are tested in uniform magnetic fields; however, for practical application, detailed knowledge of their behaviour in inhomogeneous magnetic fields (IMFs) is necessary. In this work, we measured IMFs with radial symmetry produced by alternate currents (AC) passing through an individual thin wire upon different placements of an ME sensor. An ME self-biased b-LN/Ni/Metglas structure with a sensitivity to the magnetic field of 120 V/T was created for IMF detection. The necessity of an external biasing magnetic field was avoided by the inclusion of a nickel layer having remanent magnetization. The ME composite shows a non-zero ME coefficient of 0.24 V/(cm · Oe) in the absence of an external DC magnetic field. It is shown that the output voltage amplitude from the ME composite, which is located in an AC IMF, is dependent on the relative position of the investigated sample and magnetic field lines. Maximum ME signal is obtained when the long side of the ME sample is perpendicular to the wire, and the symmetry plane which divides the long side into two similar pieces contains the wire axis. In the frequency range from 400 Hz to 1000 Hz in the absence of vibrational and other noises, the detection limit amounts to (2 ± 0.4) nT/Hz^1/2.