Spontaneous Magnetization Reversal in La_0.7Sr_0.3MnO₃ and LaMnO₃ Thin Films

Utilizing many techniques (bulk magnetometry, neutron reflectometry and x-ray magnetic circular dichroism), we have discovered and explored spontaneous magnetization reversal in high-quality complex oxide La_0.7Sr_0.3MnO₃ and LaMnO₃ thin films grown via pulsed laser deposition, with reflection high energy electron diffraction (RHEED) monitoring to verify layer-by-layer growth. The spontaneous magnetization reversal occurs at low applied fields and originates from the competition between different types of magnetic order. An early explanation for this strong negative magnetization was increased Sr content at the interface, however, this is not present in our films, particularly in LaMnO₃. While the overall effect is observed across many sample thicknesses and oxygen growth pressures, these parameters affect the behavior systematically. Despite excellent film quality, magnetocaloric measurements suggest that these films have comparable relative cooling powers to their nanoparticle partners.