Low-frequency magnetic sensing by magnetoelectric metglas/bidomain LiNbO3 long bars

We present an investigation into the magnetic sensing performance of magnetoelectric bilayered metglas / bidomain LiNbO3 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+128o-cut LiNbO3 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/Hz1/2 at 10 Hz and to 68 pT/Hz1/2 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/Hz1/2 at a resonance frequency of 244 Hz and 1.2 pT/Hz1/2 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.publishe

Magnetoelectric metglas/bidomain y + 140°-cut lithium niobate composite for sensing fT magnetic fields

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 “head-to-head” bidomain structure and metglas used as a magnetostrictive layer. A series of bidomain lithium niobate crystals were prepared by annealing under conditions of Li2O outdiffusion from LiNbO3 with a resultant growth of an inversion domain. The measured quasi-static magnetoelectric coupling coefficient achieved |αE31| = 1.9 V·(cm·Oe)–1. At a bending resonance frequency of 6862 Hz, we found a giant |αE31| value up to 1704 V·(cm·Oe)–1. Furthermore, the equivalent magnetic noise spectral density of the investigated composite material was only 92 fT/Hz1/2, 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.publishe

Non-local dispersion and ultrasonic tunneling in concentrationally graded solids

The non-local dispersion of longitudinal ultrasonic waves is shown to appear in the heterogeneous solids due to continuous spatial distributions of their density and/or elasticity (gradient solids). This dispersion gives rise to the diversity of ultrasonic transmittance spectra, including the broadband total reflectance plateau, total transmission and tunneling spectral ranges. The ultrasonic wave fields in gradient solids, formed by interference of forward and backward travelling waves as well as by evanescent and antievanescent modes are examined in the framework of exactly solvable models of media with continuously distributed density and elasticity. Examples of transmittance spectra for both metal and semiconductor gradient structures are presented, and the generality of concept of artificial non-local dispersion for gradient composite materials is considered. It should also be noted that the wave equation for acoustic waves in gradient media with a constant elasticity modulus and a certain predetermined density distribution reduces to an equation describing the electromagnetic wave propagation in transparent dielectric media. This formal similarity shows that the concept of non-local dispersion is common for both optical and acoustic phenomena, which opens the way to the direct use of physical concepts and exact mathematical solutions, developed for gradient optics, to solve the corresponding acoustic problems

Electrophysical properties, memristive and resistive switching of charged domain walls in lithium niobate

Charged domain walls (CDWs) in ferroelectric materials raise both fundamental and practical interest due to their electrophysical properties differing from bulk ones. On a microstructure level, CDWs in ferroelectrics are 2D defects separating regions with different spontaneous polarization vector directions. Screening of electric field of the CDW's bound ionic charges by mobile carriers leads to the formation of elongated narrow channels with an elevated conductivity in initially dielectric materials. Controlling the position and inclination angle of CDW relative to the spontaneous polarization direction, one can change its conductivity over a wide range thus providing good opportunities for developing memory devices, including neuromorphic systems. This review describes the state of art in the formation and application of CDWs in single crystal uniaxial ferroelectric lithium niobate (LiNbO3, LN), as resistive and memristive switching devices. The main CDWs formation methods in single crystal and thin-film LN have been described, and modern data have been presented on the electrophysical properties and electrical conductivity control methods of CDWs. Prospects of CDWs application in resistive and memristive switching memory devices have been discussed

Detection of inhomogeneous magnetic fields using magnetoelectric composites

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/Hz1/2

Detection of inhomogeneous magnetic fields using magnetoelectric composites

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/Hz1/2

Tailoring of stable induced domains near a charged domain wall in lithium niobate by probe microscopy

Ferroelectric lithium niobate (LiNbO3) crystals with an engineered domain structure have a number of applications in optical systems for generation of multiple laser radiation harmonics, acoustooptics, precision actuators, vibration and magnetic field sensors, including those for high-temperature applications, and prospectively, in non-volatile computer memory. We have studied the effect of charged domain boundary on the formation of induced domain structures in congruent lithium niobate (LiNbO3) crystals at the non-polar x-cut. Bi- and polydomain ferroelectric structures containing charged “head-to-head” and “tail-to-tail” type domain boundaries have been formed in the specimens using diffusion annealing in air ambient close to the Curie temperature and infrared annealing in an oxygen free environment. The surface potential near the charged domain wall has been studied using an atomic force microscope (AFM) in Kelvin mode. We have studied surface wedge-shaped induced microscopic domains formed at the charged domain boundary and far from that boundary by applying electric potential to the AFM cantilever which was in contact with the crystal surface. We have demonstrated that the morphology of the induced domain structure depends on the electrical conductivity of the crystals. The charged “head-to-head” domain boundary has a screening effect on the shape and size of the domain induced at the domain wall. Single wedge-shaped domains forming during local repolarization of reduced lithium niobate crystals at the AFM cantilever split into families of microscopic domains in the form of codirectional beams emerging from a common formation site. The charged domain wall affects the topography of the specimens by inducing the formation of an elongated trench, coincident with the charged boundary, during reduction annealing

Magnetoelectric effect in three-layered gradient LiNbO3/Ni/Metglas composites

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 Hdc = 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

Tailoring of stable induced domains near a charged domain wall in lithium niobate by probe microscopy

Ferroelectric lithium niobate (LiNbO3) crystals with an engineered domain structure have a number of applications in optical systems for generation of multiple laser radiation harmonics, acoustooptics, precision actuators, vibration and magnetic field sensors, including those for high-temperature applications, and prospectively, in non-volatile computer memory. We have studied the effect of charged domain boundary on the formation of induced domain structures in congruent lithium niobate (LiNbO3) crystals at the non-polar x-cut. Bi- and polydomain ferroelectric structures containing charged “head-to-head” and “tail-to-tail” type domain boundaries have been formed in the specimens using diffusion annealing in air ambient close to the Curie temperature and infrared annealing in an oxygen free environment. The surface potential near the charged domain wall has been studied using an atomic force microscope (AFM) in Kelvin mode. We have studied surface wedge-shaped induced microscopic domains formed at the charged domain boundary and far from that boundary by applying electric potential to the AFM cantilever which was in contact with the crystal surface. We have demonstrated that the morphology of the induced domain structure depends on the electrical conductivity of the crystals. The charged “head-to-head” domain boundary has a screening effect on the shape and size of the domain induced at the domain wall. Single wedge-shaped domains forming during local repolarization of reduced lithium niobate crystals at the AFM cantilever split into families of microscopic domains in the form of codirectional beams emerging from a common formation site. The charged domain wall affects the topography of the specimens by inducing the formation of an elongated trench, coincident with the charged boundary, during reduction annealing

Degradation of the electrical conductivity of charged domain walls in reduced lithium niobate crystals

In this work, the effect of long-term room temperature exposure on the electrical conductivity of the charged domain wall (CDWs) in nonpolar x-cut congruent lithium niobate (LiNbO3, LN) crystals has been studied. Bidomain ferroelectric structures containing head-to-head charged domain boundaries have been produced by diffusion annealing in air near the Curie temperature and by infrared annealing. The crystals have been reduction annealed in a nitrogen atmosphere for the formation of color centers and growth of the electrical conductivity. The current measured during the recording of the I-V curves of the specimens using scanning probe microscope after room temperature exposure for 91 days has been found to decrease. The effect of storage conditions on the electrical conductivity of the CDWs has been studied. Degradation of the electrical conductivity does not originate from the effect of environment on the crystal surface. It has been hypothesized that the degradation is caused by distribution of charge carriers shielding the bound charge of the CDWs