Scaling analysis of magnetic-thermal behaviors in ferromagnetic insulator LaCoO3 thin film

The structure, surface topography and magnetic properties of LaCoO3 (LCO) thin films deposited epitaxially on the SrTiO3 substrates have been investigated in detail. The LCO thin films show a typical ferromagnetic-paramagnetic (FM-PM) phase transition at 78 K. Based on the measurements of isothermal magnetization around the Curie point, the magnetic entropy change (Delta S-M) of LCO thin films under various applied magnetic fields were obtained. By utilizing scaling theory, all of the Delta S-M curves can be re-scaled, confirming that the FM-PM phase transition is second-order magnetic phase transition. Moreover, the magnetic entropy change -Delta S-M features a maximum around T-C, whereas, power law fitting of -Delta S-M(max) with H gives n = 0.9704, which is obviously deviating from the standard value n = 2/3 for the Landau mean field model. This indicates that the mean field theory cannot be used to explain the critical behavior of LCO thin films which implies that the critical behavior of LCO thin films may involve complex magnetic interactions. These interactions are correlated with a long-term puzzling finding in this system why its Curie point is always around 80 K regardless of the different fabrication methods and conditions used in the film growth.

Automated summary

The study focused on the structure, surface topography and magnetic properties of LaCoO3 thin films, revealing a typical ferromagnetic-paramagnetic phase transition at 78K. Results from measurements and scaling theory confirmed a second-order magnetic phase transition, while the deviation from the Landau mean field model suggests complex magnetic interactions are at play in these films' critical behavior.