Multistep Accelerated Aging of Magnetic Field Sensors Based on Nanostructured La–Sr–Mn–O Thin Films
We present results of investigation of accelerated aging influence on electrical resistivity and magnetoresistance (MR) of nanostructured La–Sr–Mn–O films used for magnetic field sensors, which could be applied in advanced scientific and industrial devices. The 400-nm-thick manganite films were grown by metal organic chemical vapor deposition technique. To investigate the effectiveness of accelerated aging, the three methods were tested: 1) thermal treatment of the sensor samples at 100 °C temperature in Ar atmosphere when film surface was uncoated; 2) thermal treatment of the samples coated prior to treatment by polymer; and 3) multistep aging including both previous methods: thermal treatment of the samples with uncoated surface in Ar atmosphere and additional thermal treatment of the coated samples. The sensor samples were studied without and in pulsed magnetic field up to 20 T. To describe the underlying processes, the kinetics of resistivity change during accelerated aging was analyzed using a stretched exponent relaxation function. It was found that the best long-term stability of resistivity in time demonstrated samples treated by a multistep accelerated aging method. All three aging methods resulted in minor influence (<1%) on MR of the films in magnetic fields up to 20 T.
Improvement in the long-term stability of parameters of encapsulated magnetic field sensors based on LaSrMnO thin films
Abstract The effectiveness of different approaches used for improvement of stability of colossal magnetoresistance-B-scalar magnetic field sensors made from polycrystalline manganite La0.83Sr0.17MnO3 thin films were considered. We show that the ageing process of sensors can be accelerated by annealing the films in Ar atmosphere at 75–125 °C and covering them by hot melt adhesive (polyethylene). Ageing kinetics of electrical resistance and magnetoresistance (MR) were investigated as well as the influence of hot melt adhesive. Despite of increased resistance only small changes of the MR and the temperature coefficient of resistance were observed. The obtained results are explained by the oxygen release, displacement or redistribution which takes place most probably in grain boundaries of polycrystalline manganites. Based on the obtained results optimal conditions for the stabilization of encapsulated sensors parameters were found resulting in the resistance drift less than 1.5% per year.
Photoreflectance characterization of vanadium-doped GaAs layers grown by metalorganic vapor phase epitaxy
Abstract We characterized the vanadium-doped (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy. The conductivity of the samples is checked by the Hall effect measurements, and it is n type with electrons concentration ranging from 2×10 13 to 2×10 17  cm −3 . We used the photoreflectance technique (PR) to study the effect of vanadium doping on the optical properties of GaAs. Our experimental results show that the built-in electric field F and the broadening parameter Γ 0 increase with V-doping concentration. Furthermore, the temperature dependence of the built-in electric field and the broadening parameter of GaAs:V samples have been investigated by PR. It has been observed that these parameters increase with increasing temperature. The decrease of the built-in electric field with decreasing temperature is due to the photovoltage effect.We characterized the vanadium-doped GaAs (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy.