Magnetoresistance and Magnetic Relaxation of La-Sr-Mn-O Films Grown on Si/SiO₂ Substrate by Pulsed Injection MOCVD

The results of magnetoresistance (MR) and resistance relaxation of nanostructured La1−xSrxMnyO3 (LSMO) films with different film thicknesses (60–480 nm) grown on Si/SiO2 substrate by the pulsed-injection MOCVD technique are presented and compared with the reference manganite LSMO/Al2O3 films of the same thickness. The MR was investigated in permanent (up to 0.7 T) and pulsed (up to 10 T) magnetic fields in the temperature range of 80–300 K, and the resistance-relaxation processes were studied after the switch-off of the magnetic pulse with an amplitude of 10 T and a duration of 200 μs. It was found that the high-field MR values were comparable for all investigated films (~−40% at 10 T), whereas the memory effects differed depending on the film thickness and substrate used for the deposition. It was demonstrated that resistance relaxation to the initial state after removal of the magnetic field occurred in two time scales: fast’ (~300 μs) and slow (longer than 10 ms). The observed fast relaxation process was analyzed using the Kolmogorov–Avrami–Fatuzzo model, taking into account the reorientation of magnetic domains into their equilibrium state. The smallest remnant resistivity values were found for the LSMO films grown on SiO2/Si substrate in comparison to the LSMO/Al2O3 films. The testing of the LSMO/SiO2/Si-based magnetic sensors in an alternating magnetic field with a half-period of 22 μs demonstrated that these films could be used for the development of fast magnetic sensors operating at room temperature. For operation at cryogenic temperature, the LSMO/SiO2/Si films could be employed only for single-pulse measurements due to magnetic-memory effects

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

The Application of a CMR-B-Scalar Sensor for the Investigation of the Electromagnetic Acceleration of Type II Superconductors

In this paper, we investigated the behavior of a type II superconducting armature when accelerated by a pulsed magnetic field generated by a single-stage pancake coil. While conducting this investigation, we performed a numerical finite element simulation and an experimental study of the magnetic field dynamics at the edge of the pancake coil when the payload was a superconducting disc made from YBa2Cu3O7−x, cooled down to 77 K. The magnetic field measurements were performed using a CMR-B-scalar sensor, which was able to measure the absolute magnitude of the magnetic field and was specifically manufactured in order to increase the sensor’s sensitivity up to 500 mT. It was obtained that type II superconducting armatures can outperform normal metals when the launch conditions are tailored to their electromagnetic properties.This article belongs to the Special Issue Magnetic Sensors and Systems for Scientific and Industrial Application

Determination of the electroporation threshold for pulses from 95 ns to 20 us

The dependences of the fraction of electroporated mouse hepatoma MH-22A cells on the pulse intensity were obtained for the cells exposed to a single square-wave electric pulse with the duration from 95 ns to 20 μs. The amplitude of an electric pulse was varied from 0.4 to 12 kV/cm. Increasing the intensity of the electric field pulse increased the fraction of electroporated cells. The electric field, which lead to a given percentage of electroporation, decreased with increasing the pulse length. The dependence of the amplitude of the electric pulse required to electroporate 50 % of mouse hepatoma MH-22A cells on the pulse duration was also determinedBiologijos katedraFizinių ir technologijos mokslų centro Puslaidininkių fizikos institutasVytauto Didžiojo universiteta

Computer controlled thermostat for the resistivity measurements of the La1-xSrxMnO3 thin films

The temperature stabilization system for the magnetoresistance measurements of the La1-xSrxMnO3 manganites is described in this paper. The thermostat cell with the Peltier heating/cooling element was manufactured specially to be placed between the poles of the electromagnet. The heat sink attached to the rear side of the Peltier element is cooled by the flowing tap water. Platinum film temperature probe was used for the temperature feedback signal. Universal multimeter “Tektronix DMM 4050” was used as a temperature meter and a regulated laboratory power supply “TTI QL 564P” was used to supply the current through the Peltier element. Both instruments were controlled by the computer software via the USB and GPIB interfaces. The software implementing a PID algorithm was written in the LabView graphical programming interface. The results show that the temperature of the sample can be changed in 2-3 minutes depending on the temperature step and is kept constant with precision of ±0.02 °C

Numerical Magneto-Mechanical Analysis of Destructive Coils with Reinforcement Cylinders of Various Thicknesses

The destructive laboratory device, generating half-period sinus-shaped magnetic field pulses of 0.15-2 ms duration is investigated numerically. The coil was placed into a steel reinforcement cylinder to resist magnetic forces, while influence of thickness of the reinforcement cylinder is considered in detail. The time-dependent non-linear magneto-mechanical model and the finite element software ANSYS are employed. On the basis of the mechanical analysis, reasonable explanation of the destruction nature is provided. The numerically obtained operation threshold value was in good agreement with experimental measurements

Inductors for high magnetic field generation

Inductors for high magnetic field generation are described. Pulsed magnetic field is generated discharging energy bank through the inductor during a short period of time. Axial magnetic field is calculated by equations using known values of pulsed current and geometric parameters of the inductor. The efficiency of energy transformation is analyzed. The possibility of non-destructive applications of single turn inductor, flux concentrator, helix inductor, and multi-section inductor is discussed. The design of pulsed magnetic inductors requires complex analysis of electrical, thermal and mechanical overloads, and the most limited factor is the destructive mechanical stress. For the first estimation the failure criteria of maximal available magnetic field inductor and the crosssectional distribution of stress intensity under action of Lorentz forces are presented. The multi-section inductor is chosen as the challenging long life construction for further experimentations in high magnetic field generation area

Single Pulse Calibration of Magnetic Field Sensors Using Mobile 43 kJ Facility

In this work we present a mobile 43 kJ pulsed magnetic field facility for single pulse calibration of magnetic field sensors. The magnetic field generator is capable of generating magnetic fields up to 40 T with pulse durations in the range of 0.3-2 ms. The high power crowbar circuit is used for the reverse voltage protection and pulse shaping purposes. The structure, the development challenges and the implemented solutions to improve the facility for the calibration of the magnetic field sensors are overviewed. The experimental data of the application of the proposed generator for the calibration of manganite magnetic field sensors are presented