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.
Magnetic Diffusion in Railguns: Measurements Using CMR-Based Sensors
Magnetic diffusion is of great importance in the domain of electromechanical energy conversion since it can be a performance-limiting mechanism. This paper deals with magnetic diffusion in the case of the rails of a railgun. The experiments benefit from the use of a new type of high magnetic-field sensor based on thin ( < 1 mum) manganite films, which exhibits a colossal magnetoresistance (CMR) effect and has very small sensitive areas (e.g., 0.5 mm times 50 mum). Some basics about CMR and the design of the sensor are given. Several sensors were used and calibrated in the course of static transient railgun experiments. Here, varying spatial field distributions due to the use of different rail materials were recorded. Magnetic-field measurements during railgun operation with projectile velocities exceeding 1000 m/s have been successfully performed. By comparison with 3-D finite-element calculations, interesting results concerning magnetic diffusion have been worked out.
Finite Difference Modeling on the Temperature Field of Substrate in Friction Surfacing
Friction surfacing is an advanced process of great potential, especially in the field of repair and reclamation of worn and damaged components. As a kind of thermal processing technology, the temperature profile and changes of the substrate in friction surfacing are important factors to get coatings of high quality. In this paper, the temperature field of the substrate during the process is simulated by finite difference method. The results are consistent with experiments, reappearing the temperature change of the substrate during friction surfacing, allowing further study on figuration and quality of coatings.