Magnetic characteristics of LaMnO3+δthin films deposited by RF magnetron sputtering in an O2/Ar mixture gas

Abstract

In this work, LaMnO3+δ thin films have been successfully fabricated by RF magnetron sputtering using differentO2/Ar flux ratios. The crystal structures, morphologies, stoichiometry, surface chemical states and magnetic properties of films are thoroughly characterized by x-ray powder diffraction (XRD), Raman spectrometer, scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS) and superconducting quantum interference device (SQUID). The magnetic characteristics of LaMnO3+δ films are systematically studied with the transformation fromMn3+ to Mn4+, which is strongly controlled by the depositedO2/Ar flux ratios.Wedemonstrate that LaMnO3+δ films undergo an antiferromagnet, the coexistence of ferromagnetism and antiferromagnetism and a robust ferromagnetism ordering by the variation ofMn3+/Mn4+ ratios. TheLMOfilm deposited in pure argon atmosphere shows negligibleFMsignal and an inconspicuous TC. With the increase of depositedO2/Ar flux ratios, the Curie temperature ofLMOfilms increases from 100Kto 224Kand then decreases to 140Kand meanwhile the irreversibility temperature fluctuates between 24Kand 100 K. The appearance of cluster glass state and the unexpected exchange bias phenomenon where the film deposited at highestO2/Ar flux ratio has aHEB ∼ 115 Oe is observed. All these evolutions of magnetization characteristics are discussed in terms of the strength of ferromagnetic interactions and the degree of competition between ferromagnetic and antiferromagnetic interactions in LaMnO3+δ films. Our work serves as prerequisites for LaMnO3-based magnetic heterostructures grown by RF magnetron sputtering.