Structural characteristics and magnetic properties of λ-MnO₂ films grown by plasma-assisted molecular beam epitaxy

High-quality λ-MnO₂ single-crystal films were fabricated on MgO (001) substrates by plasma-assisted molecular beam epitaxy. The structural characteristics and magnetic properties of the films were studied. Two magnetic transition temperatures, T1 and T2, were observed from the films. Their magnetic behavior differed from that of bulk polycrystalline samples synthesized by removing Li ions from the parent LiMn₂O₄. The first, T1, setting at around 20 K, corresponded to long-range antiferromagnetic ordering similar to that observed in bulk at 32 K. T2, set at 43 K, corresponded to weak long-range ferromagnetic ordering among net magnetization of clusters, in which short-range antiferromagnetic ordering existed. T1 shifted to lower temperature with decreasing film thickness, which indicated that the proximity of the interface and strain played a key role in determining the transition temperature.