Relaxation of Ferromagnetic and Paramagnetic State of Thin La-Sr-MnO Films Exposed by High-Power Picosecond Duration Optical Pulses

We have investigated resistivity rise and relaxation of thin epitaxial (EP) and nanostructured polycrystalline (NP) La-Sr-MnO films after thermal shock. Samples of 400-nm thickness La
_0.83
Sr
_0.17
MnO
₃
were grown on LaAlO
₃
substrate for EP films, and on “lucalox” for NP films. The thermal shocks were induced by 1064-nm 30-ps Nd:YAG laser pulses with pulse energy at the sample between 1.5 and 2 mJ. Samples were treated by single laser pulse at different ambient temperatures when the film was in ferromagnetic or paramagnetic state. In the films at temperatures (T
₀
) lower than phase transition temperature (T
_m
) immediately after the laser pulse, the resistance of the sample has increased. It was found that the rise time of resistance response increases with increase of T
₀
in the range from few hundred ps to several ns. Meanwhile, the time of total relaxation of resistance back to initial level was in the range from 10 to 35 μs. For both types of films, the experimental results of cooling process showed longer relaxation time than that of obtained in theoretical modeling. Possible reasons were discussed taking into account magnetic ordering processes. The obtained results help to evaluate the influence of fast temperature changes during high pulsed magnetic field measurements with B-scalar sensors based on La-Sr-MnO films.