We present an investigation into the magnetic sensing performance of magnetoelectric bilayered metglas / bidomain LiNbO 3 long thin bars operating in a cantilever or free vibrating regime and under quasi-static and low-frequency resonant conditions. Bidomain single crystals of Y+128 o-cut LiNbO 3 were engineered by an improved diffusion annealing technique with a polarization macrodomain structure of the "head-to-head" and "tail-to-tail" type. Long composite bars with lengths of 30, 40 and 45 mm, as well as with and without attached small tip proof masses, were studied. ME coefficients as large as 550 V/cm•Oe, corresponding to a conversion ratio of 27.5 V/Oe, were obtained under resonance conditions at frequencies of the order of 100 Hz in magnetic bias fields as low as 2 Oe. Equivalent magnetic noise spectral densities down to 120 pT/Hz 1/2 at 10 Hz and to 68 pT/Hz 1/2 at a resonance frequency as low as 81 Hz were obtained for the 45 mm long cantilever bar with a tip proof mass of 1.2 g. In the same composite without any added mass the magnetic noise was shown to be as low as 37 pT/Hz 1/2 at a resonance frequency of 244 Hz and 1.2 pT/Hz 1/2 at 1335 Hz in a fixed cantilever and free vibrating regimes, respectively. A simple unidimensional dynamic model predicted the possibility to drop the low-frequency magnetic noise by more than one order of magnitude in case all the extrinsic noise sources are suppressed, especially those related to external vibrations, and the thickness ratio of the magnetic-to-piezoelectric phases is optimized. Thus, we have shown that such systems might find use in simple and sensitive room-temperature low-frequency magnetic sensors, e.g., for biomedical applications.

Polymer-based magnetoelectric composite materials have attracted a lot of attention due to their high potential in various types of applications as magnetic field sensors, energy harvesting, and biomedical devices. Current researches are focused on the increase in the efficiency of magnetoelectric transformation. In this work, a new strategy of arrangement of clusters of magnetic nanoparticles by an external magnetic field in PVDF and PFVD-TrFE matrixes is proposed to increase the voltage coefficient (αME) of the magnetoelectric effect. Another strategy is the use of 3-component composites through the inclusion of piezoelectric BaTiO3 particles. Developed strategies allow us to increase the αME value from ~5 mV/cm·Oe for the composite of randomly distributed CoFe2O4 nanoparticles in PVDF matrix to ~18.5 mV/cm·Oe for a composite of magnetic particles in PVDF-TrFE matrix with 5%wt of piezoelectric particles. The applicability of such materials as bioactive surface is demonstrated on neural crest stem cell cultures.

We investigated the magnetoelectric properties of a new laminate composite material based on y+140°-cut congruent lithium niobate piezoelectric plates with an antiparallel polarized "headto-head" bidomain structure and metglas used as a magnetostrictive layer. A series of bidomain lithium niobate crystals were prepared by annealing under conditions of Li 2 O outdiffusion from LiNbO 3 with a resultant growth of an inversion domain. The measured quasi-static magnetoelectric coupling coefficient achieved |α E31 | = 1.9 V•(cm•Oe)-1. At a bending resonance frequency of 6862 Hz, we found a giant |α E31 | value up to 1704 V•(cm•Oe)-1. Furthermore, the equivalent magnetic noise spectral density of the investigated composite material was only 92 fT/Hz 1/2 , a record value for such a low operation frequency. The magnetic-field detection limit of the laminated composite was found to be as low as 200 fT in direct measurements without any additional shielding from external noises.

We present a low-frequency sensor for the detection of vibrations, with a sub-nm amplitude, based on a cantilever made of a single-crystalline lithium niobate (LiNbO3) plate, with a bidomain ferroelectric structure. The sensitivity of the sensor-to-sinusoidal vibrational excitations was measured in terms of displacement as well as of acceleration amplitude. We show a linear behavior of the response, with the vibrational displacement amplitude in the entire studied frequency range up to 150 Hz. The sensitivity of the developed sensor varies from minimum values of 20 μV/nm and 7 V/g (where g = 9.81 m/s2 is the gravitational acceleration), at a frequency of 23 Hz, to peak values of 92.5 mV/nm and 2443 V/g, at the mechanical resonance of the cantilever at 97.25 Hz. The smallest detectable vibration depended on the excitation frequency and varied from 100 nm, at 7 Hz, to 0.1 nm, at frequencies above 38 Hz. Sensors using bidomain lithium niobate single crystals, as sensitive elements, are promising for the detection of ultra-weak low-frequency vibrations in a wide temperature range and in harsh environments.

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