N. Žurauskienė

Nanostructured thin manganite films in megagauss magnetic field

We report on the use of the colossal magnetoresistance (CMR) effect in manganites for the measurement of pulsed magnetic fields up to the megagauss limit. To increase the application range in a magnetic field, we fabricated nanostructured La-Sr-Mn-O films consisting of nanocrystallites cummulated into clusters separated by highly amorphous inter-cluster boundaries. We demonstrate that the CMR effect does not saturate in these films at 77 K up to 91.4 T. Moreover, the magnetoresistance behavior at 290 K shows that nanostructured manganite films are promising candidates for the development of magnetic field scalar sensors operating in wide field and temperature ranges.

Pulsed magnetic field measurement system based on colossal magnetoresistance-B-scalar sensors for railgun investigation

A high pulsed magnetic field measurement system based on the use of CMR-B-scalar sensors was developed for the investigations of the electrodynamic processes in electromagnetic launchers. The system consists of four independent modules (channels) which are controlled by a personal computer. Each channel is equipped with a CMR-B-scalar sensor connected to the measurement device-B-scalar meter. The system is able to measure the magnitude of pulsed magnetic fields from 0.3 T to 20 T in the range from DC up to 20 kHz independently of the magnetic field direction. The measurement equipment circuit is electrically separated from the ground and shielded against low and high frequency electromagnetic noise. The B-scalar meters can be operated in the presence of ambient pulsed magnetic fields with amplitudes up to 0.2 T and frequencies higher than 1 kHz. The recorded signals can be transmitted to a personal computer in a distance of 25 m by means of a fiber optic link. The system was tested using the electromagnetic railgun RAFIRA installed at the French-German Research Institute of Saint-Louis, France.

Manganite Sensor for Measurements of Magnetic Field Disturbances of Pulsed Actuators

Magnetic field sensors based on polycrystalline La0.83Sr0.17MnO3 films were used to measure the magnetic field distribution and disturbances during the operation of an electromagnetic launcher. Hollow cylinders made from dural aluminum and iron were used as propelled objects inside the solenoidal coil. The obtained results revealed the ability of manganite sensors to rapidly measure changing high magnetic fields of arbitrary waveforms.

AGEING EFFECTS ON ELECTRICAL RESISTIVITY AND MAGNETORESISTANCE OF NANOSTRUCTURED MANGANITE FILMS

The long-term stability of electrical resistance and magnetoresistance in nanostructured La1-xSrxMnO3 (x = 0.17) manganite thin films grown on lucalox (Al2O3 + MgO) substrate by the MOCVD method was investigated. It was found that the storage of up to 3 months of the free surfaces of these films in normal atmosphere (air) conditions increases their resistivity by almost two times, while the annealing of the films in an Ar atmosphere at 450 °C decreases their resistivity only by 15%. It was concluded that the final increase of resistivity is determined by a long-term relaxation of the grain boundaries in the nanostructured films. The magnetoresistance of the films does not change significantly, which produces an advantage for magnetic field sensor applications. The passive protective coating of the free surfaces of the films stabilizes their electrical and magnetic properties. The results were analysed using various electron scattering mechanisms when the films were in a ferromagnetic state, and the Mott’s variable range hopping model when they were in a paramagnetic insulating state.

Influence of Sr Content on CMR Effect in Polycrystalline La_{1-x}Sr_{x}MnO_{3} 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.

Fast reversible thermoelectrical switching in manganite thin films

The authors report on fast reversible switching of epitaxial and polycrystalline La0.83Sr0.17MnO3 films from the ferromagnetic to the paramagnetic state induced by high power nanosecond electrical pulses. It was demonstrated that for the epitaxial films adiabatic and uniform Joule heating is the reason of the switching. For polycrystalline films, electronic processes reduce the film resistance within a subnanosecond. For longer times, adiabatic nonhomogeneous heating plays the main role in the switching dynamics. Possible device applications of this phenomenon are also discussed.

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

Abstract 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.

Manganite Based Strong Magnetic Field Sensors Used for Magnetocumulative Generators

The effects of strong pulsed magnetic field and shock waves on the electrical properties of La 0.67 Ca 0.33 MnO 3 and La 0.7 Sr 0.3 MnO 3 thin films were investigated. It was demonstrated that these films could be used to measure the magnetic fields produced by magnetocumulative generators. Possible ways to design fast magnetic field sensors operating at room temperature are also discussed.

Magnetoresistance anisotropy of ultrathin epitaxial La0.83Sr0.17MnO3 films

We present the study of temperature dependence of resistivity (ρ), magnetoresistance (MR), and magnetoresistance anisotropy (AMR) of thin epitaxial La0.83Sr0.17MnO3 films. The films with thickness from 4 nm to 140 nm were grown on an NdGaO3 (001) substrate by a pulsed injection metal organic chemical vapor deposition technique. We demonstrate that the resistivity of these films significantly increases and the temperature Tm of the resistivity maximum in ρ(T) dependence decreases with the decrease of film thickness. The anisotropy of ρ(T) dependence with respect to the electrical current direction along the [100] or [010] crystallographic axis of the film is found for ultrathin films (4–8 nm) at temperatures close to Tm. Both MR and AMR, measured in magnetic fields up to 0.7 T applied in the film plane parallel and perpendicular to the current direction, have shown strong dependence on the film thickness. It was also found that the anisotropy of magnetoresistance could change its sign from positive (thicke...