Exchange bias effect in epitaxial La0.67Ca0.33MnO3/SrMnO3 thin film structure.

Bilayers consisting of La_0.67Ca_0.33MnO₃ (LCMO) and SrMnO₃ (SMO) have been prepared by pulsed-laser deposition on SrTiO₃ (001) substrates. Unconventional magnetic coupling was found after cooling in a small field. The LCMO/SMO bilayers exhibit an exchange bias field of 209 Oe, which vanishes as the temperature rises above 90 K. A small magnetization has been found above the Curie temperature of the pure LCMO thin films. Spin-cluster-like antiferromagnetic (AFM)/ferromagnetic (FM) clusters have been deduced to exist at the interface due to the competing types of magnetic order at the interface. The magnetic relaxation is found to follow a doubleexponential equation and a slow relaxation process is observed due to the strong exchange coupling between AFM/FM clusters and the LCMO layer. We speculate that the short-range high-temperature FM order of the Mn³⁺ and Mn⁴⁺ moments above the Curie temperature at the interface gives rise to the magnetic regions that pin the FM LCMO layer as the temperature decreases. [ABSTRACT FROM AUTHOR]