Increase of operating temperature of magnetic field sensors based on La–Sr–Mn–O films with Mn excess

Abstract

The results of Mn excess influence on the magnetoresistive properties of nanostructured La 1–x Sr x Mn y O 3±δ films grown on polycrystalline Al 2 O 3 substrates by pulsed-injection metal-organic chemical vapor deposition technique are presented. The electrical transport properties and magnetoresistance of these films were investigated in the temperature range of 77–363 K in pulsed magnetic fields up to 20 T. The results were analyzed from the perspective of using these films for magnetic field sensors operating at high temperatures. It was obtained that the increase of Mn/(La + Sr) ratio from 1.05 to 1.15 leads to the increase of metal–insulator transition temperature from 240 to 270 K. This behavior was associated with the presence of (La + Sr) vacancies, which act as self-dopants. At temperatures higher than 340 K, the highest magnetoresistance values were obtained for films with 15% Mn excess. These results allowed us to produce pulsed magnetic field sensors operating at ambient temperatures up to 90 °C.