Magnetoresistance and its relaxation of nanostructured La-Sr-Mn-Co-O films: Application for low temperature magnetic sensors

•Thin nanostructured La-Sr-Mn-Co-O/Al2O3 films have been fabricated by PI MOCVD.•Magnetoresistance and resistance relaxation have been studied in La-Sr-Mn-Co-O films.•Co-doped manganite films exhibit temperature-insensitive magnetoresistance at 4-200 K.•Co-doped manganite is promising material for development of cryogenic magnetic sensors. The results of magnetoresistance (MR) and resistance relaxation of nanostructured La1-xSrx(Mn1-yCoy)zO3 (LCMCO) films doped with different Co amount (Co/(La + Sr) = 0.06; 0.12; 0.14) while keeping constant Sr (x = 0.2) deposited by Pulsed Injection MOCVD technique, are presented and compared with the reference manganite La0.8Sr0.2MnzO3 (LSMO) film. The MR was investigated in pulsed magnetic fields up to 25 T in the temperature range 4–200 K while the relaxation processes were studied in pulsed fields up to 10 T and temperatures in the range of 100–300 K. It was demonstrated that at low temperatures the MR(%) and sensitivity S(mV/T) of Co-doped films have significantly higher values in comparison with the LSMO ones, and increases with increase of Co/(La + Sr) ratio. The observed temperature-insensitive MR in the range of 4–200 K suggests possibility to use these films for sensors applications. The magnetic memory effects were investigated as resistance relaxation processes after the switch-off of the magnetic field pulse. The observed ‘fast’ (~300 μs) resistance relaxation was analyzed by using the Kolmogorov–Avrami–Fatuzzo model, taking into account the reorientation of magnetic domains into their equilibrium state, while the ‘slow’ process (>ms) was explained by using the Kohlrausch–Williams–Watts model considering the interaction of the magnetic moments in disordered grain boundaries. It was concluded that Co-doped nanostructured manganite LSMCO films having a higher sensitivity and lower memory effects in comparison with the LSMO films could be used for the development of pulsed magnetic field sensors operating at low temperatures.