Investigation of magnetoresistance and its anisotropy of thin polycrystalline La0.83Sr0.17MnO3 films in high pulsed magnetic fields / N. Žurauskienė, S. Keršulis, L. Medišauskas, S. Tolvaišienė.

The results on the study of grain boundary effects and influence of film deposition conditions on the magnetoresistance and its anisotropy in polycrystalline La0.83Sr0.17MnO3 films are presented. The magnetoresistance was measured in high pulsed magnetic fields up to 25 T (pulse duration approximate to 0.6 ms) in the temperature range of 120-300 K. A modified Mott hopping model was applied to describe the main behavior of high-field magnetoresistance for both ferromagnetic and paramagnetic phases of the polycrystalline films by taking into account the demagnetization field of the films measured in low magnetic fields perpendicular to film plane. It was also found that to obtain the higher magnetoresistance saturation field at room temperature it is necessary to use the films with smaller crystallites (D approximate to 100 nm). Such films could be used for design of megagauss pulsed magnetic field sensors

Fast two-stage protector against electromagnetic pulse based on electroresistance effect in polycrystalline La-Sr(Ca)-Mn-O films

The electroresistance (ER) effect in polycrystalline films of La0.83Sr0.17MnO3 and La0.7Ca0.3MnO3 was investigated in the temperature range of (5 – 290) K using high power sub-nanosecond rise time electrical pulses with amplitude up to 1 kV. It was obtained that conductance vs. voltage dependences are nonlinear and could be well fitted by empirical formula G = G0 + Gα · Uα; where G is conductance, U is the voltage applied across the sample, G0 is the conductance at low voltage, and Gα and α are the parameters related to the electrical transport mechanism. Parameters α for La-Ca-Mn-O and La-Sr-Mn-O were 1.5 and 1.33 respectively. It was obtained that there are two regions of the electroresistance vs. temperature dependence for both films: low temperature region where ER exhibits very slow dependence on temperature and high temperature region where ER significantly decreases with temperature. It was demonstrated that polycrystalline manganite films can be used for the development of protectors against short electromagnetic pulse (EMP), and fast twostage protector operating at cryogenic temperatures (80 K) is proposed

Influence of Sr content on CMR effect in polycrystalline La1-xSrxMnO3 thin films

The magnetoresistance of thin polycrystalline La1-xSrxMnO3 films deposited on lucalox substrate using metal organic chemical vapor deposition technique was investigated in pulsed magnetic fields up to 18 T in the temperature range 100-320 K. The influence of film preparation conditions, ambient temperature variation and Sr content is analyzed in order to determine the optimal conditions for the design of CMR-B-scalar magnetic field sensor based on thin manganite film, operating at room temperature

Hybrid graphene-manganite thin film structure for magnetoresistive sensor application

An increasing demand of magnetic field sensors with high sensitivity at room temperatures and spatial resolution at micro-nanoscales has resulted in numerous investigations of physical phenomena in advanced materials, and fabrication of novel magnetoresistive devices. In this study the novel magnetic field sensor based on combination of a single layer graphene (SLG) and thin nanostructured manganite La0.8Sr0.2MnO3 (LSMO) film—hybrid graphene-manganite (GM) structure, is proposed and fabricated. The hybrid GM structure employs the properties of two materials—SLG and LSMO—on the nanoscale level and results in the enhanced sensitivity to magnetic field of the hybrid sensor on the macroscopic level. Such result is achieved by designing the hybrid GM sensor in a Wheatstone half-bridge which enables to employ in the device operation two effects of nanomaterials—large Lorentz force induced positive magnetoresistance of graphene and colossal negative magnetoresistance of nanostructured manganite film, and significantly increase the sensitivity S of the hybrid GM sensor in comparison with the individual SLG and LSMO sensors: S = 5.5 mV T−1 for SLG, 14.5 mV T−1 for LSMO and 20 mV T−1 for hybrid GM at 0.5 T, when supply voltage was 1.249 V. The hybrid GM sensor operates in the range of (0.1–2.3) T and has lower sensitivity to temperature variations in comparison to the manganite sensor. Moreover, it can be applied for position sensing. The ability to control sensor’s characteristics by changing technological conditions of the fabrication of hybrid structure and tuning the nanostructure properties of manganite film is discussed

High pulsed magnetic field sensor based on La-Ca-Mn-O thin polycrystalline films

It is demonstrated that polycrystalline La0.33Ca0.67MnO3 thin film sensors can be used to measure pulsed strong magnetic fields with microsecond duration rise and decay times. The response characteristics of these sensors were investigated using 0.7-1.0 ms duration bell-shaped magnetic field pulses of 10-20 T amplitudes andby using special waveform magnetic field pulses with amplitudes of 40 T and decay times of 50ms. The response of these magnetic field sensors was compared with those of conventional loop sensors and Faraday rotation sensors using Bi12SiO20 single crystals as a known standard

Colossal magnetoresistance properties of La0.83Sr0.17MnO3 thin films grown by MOCVD on Lucalox substrate

The magnetoresistance (MR) of polycrystalline La0.83Sr0.17MnO3 thin films have been studied in high pulsed magnetic fields up to 38 T in the temperature range 100–300 K. The lucalox substrates were used to obtain polycrystalline structures with naturally formed grain boundaries (GBs) and crystallites whose dimensions were determined by film deposition temperature. It was found that the MR value is highest in the films having smallest crystallites. The main behaviour of high-field MR was analysed using modified Mott’s hopping model assuming that the GBs might be ferromagnetic with a Curie temperature T C being reduced in comparison with that of the crystallites interior

Compact Square-Wave Pulse Electroporator with Controlled Electroporation Efficiency and Cell Viability

The design and development of a compact square-wave pulse generator for the electroporation of biological cells is presented. This electroporator can generate square-wave pulses with durations from 3 μs up to 10 ms, voltage amplitudes up to 3500 V, and currents up to 250 A. The quantity of the accumulated energy is optimized by means of a variable capacitor bank. The pulse forming unit design uses a crowbar circuit, which gives better control of the pulse form and its duration, independent of the load impedance. In such cases, the square-wave pulse form ensures better control of electroporation efficiency by choosing parameters determined in advance. The device has an integrated graphic LCD screen and measurement modules for the visualization of the current pulse, allowing for express control of the electroporation quality and does not require an external oscilloscope for current pulse recording. This electroporator was tested on suspensions of Saccharomyces cerevisiae yeast cells, during which, it was demonstrated that the application of such square-wave pulses ensured better control of the electroporation efficiency and cell viability after treatment using the pulsed electric field (PEF).This article belongs to the Special Issue Information Technologies and ElectronicsThis work was partly funded by “Geozondas” Ltd. Implementing an EU structural investment project 01.2.1-MITA-T-851-02-0004 under measure “Inocekiai.

The Influence of Voltage on Gliding Arc Discharge Characteristics, the Composition of Air Plasma, and the Properties of BG-11 Medium

A gliding arc discharge (GAD) plasma device has been developed and tested. Possible applications areas for GAD plasma could be microalgae suspension treatments and the creation of plasma-activated water. To understand its behavior, the influence of the input power on the electrical characteristics of the generated GAD plasma was investigated using an oscilloscope. The waveforms of the voltage and current of GAD plasma are presented. The duration of the discharge time and the evolution of the arc during discharge were determined and investigated. It was revealed that the increase in the output voltage prolonged the duration of the arc discharge. The composition of the air plasma was investigated using a flame-emission spectrometer and acousto-optic emission spectrometer. It was revealed that the main species in the emission spectra of the GAD air plasma were N2, N2+, N+, NO, and O species. Furthermore, the increase in the input power enhanced the ionization degree of the air plasma and increased the intensities of the emission lines associated with N2+, NO, and O species. An increase in the conductivity of the BG-11 medium was observed. Physicochemical analyses of the plasma-activated BG-11 medium indicated an increase in the concentration of nitrite and nitrate ions and hydrogen peroxide with an enhancement of the voltage

Measurement System for Short-Pulsed Magnetic Fields

A measurement system based on the colossal magnetoresistance CMR-B-scalar sensor was developed for the measurement of short-duration high-amplitude magnetic fields. The system consists of a magnetic field sensor made from thin nanostructured manganite film with minimized memory effect, and a magnetic field recording module. The memory effect of the La1−xSrx(Mn1−yCoy)zO3 manganite films doped with different amounts of Co and Mn was investigated by measuring the magnetoresistance (MR) and resistance relaxation in pulsed magnetic fields up to 20 T in the temperature range of 80–365 K. It was found that for low-temperature applications, films doped with Co (LSMCO) are preferable due to the minimized magnetic memory effect at these temperatures, compared with LSMO films without Co. For applications at temperatures higher than room temperature, nanostructured manganite LSMO films with increased Mn content above the stoichiometric level have to be used. These films do not exhibit magnetic memory effects and have higher MR values. To avoid parasitic signal due to electromotive forces appearing in the transmission line of the sensor during measurement of short-pulsed magnetic fields, a bipolar-pulsed voltage supply for the sensor was used. For signal recording, a measurement module consisting of a pulsed voltage generator with a frequency up to 12.5 MHz, a 16-bit ADC with a sampling rate of 25 MHz, and a microprocessor was proposed. The circuit of the measurement module was shielded against low- and high-frequency electromagnetic noise, and the recorded signal was transmitted to a personal computer using a fiber optic link. The system was tested using magnetic field generators, generating magnetic fields with pulse durations ranging from 3 to 20 μs. The developed magnetic field measurement system can be used for the measurement of high-pulsed magnetic fields with pulse durations in the order of microseconds in different fields of science and industry