Spin inhomogeneities at the interface and inverted hysteresis loop in La0.7Sr0.3MnO3/SrTiO3

An inverted hysteresis loop (IHL) exhibits negative coercivity and remanence, and has been ascribed to various mechanisms ranging from exchange coupling to competing anisotropies and even experimental artifacts. Here, we investigate the IHL behavior of monolithic La0.7Sr0.3MnO3 (LSMO) film using magnetization and ferromagnetic resonance (FMR) studies at 300 K. FMR measurements reveal the presence of fourfold (K-4 = 5.7 x 10(2) erg cm(-3)), uniaxial (K-u = 1.9 x 10(2) erg cm(-3)), and exchange (K-A/F = -1.15 x 10(3) erg cm(-3)) anisotropy. It is known that the competition of fourfold and uniaxial anisotropy can lead to an IHL. Furthermore, magnetic measurements exhibit positive exchange bias (EB), which could also lead to an IHL. The appearance of positive EB in monolithic LSMO film indicates the presence of secondary phases and an antiferromagnetic (AFM) coupling between the phases. We show unambiguously that the observed IHL is a result of interfacial exchange coupling in the LSMO film. Using FMR, we verify the AFM coupling at the interface and, in conjunction with the results of an earlier report, we develop an intuitive picture for the spin arrangement at the interface. Our study reveals a complex interface physics in LSMO/SrTiO3 (STO), whose understanding may generate new pathways for the development of novel functionalities in LSMO.