Nanoscale Res Lett (2007) 2:81–86 DOI 10.1007/s11671-006-9034-4 N A N O E X P R E S S Synthesis, structure and magnetic properties of b-MnO2 nanorods Hae Jin Kim Æ Jin Bae Lee Æ Young-Min Kim Æ Myung-Hwa Jung Æ Z. Jaglicˇic´ Æ P. Umek Æ J. Dolinsˇek Published online: 11 January 2007 to the authors 2007 Abstract We present synthesis, structure and magnetic properties of structurally well-ordered sin- gle-crystalline b-MnO2 nanorods of 50–100 nm diame- ter and several lm length. Thorough structural characterization shows that the basic b-MnO2 material is covered by a thin surface layer (~2.5 nm) of a-Mn2O3 phase with a reduced Mn valence that adds its own magnetic signal to the total magnetization of the b-MnO2 nanorods. The relatively complicated temper- ature-dependent magnetism of the nanorods can be explained in terms of a superposition of bulk magnetic properties of spatially segregated b-MnO2 and a-Mn2O3 constituent phases and the soft ferromagnetism of the thin interface layer between these two phases. Keywords Self-assembled nanorods oxides Nanoscale magnetism Manganese H. J. Kim J. B. Lee Energy Nano Material Team, Korea Basic Science Institute, Daejeon 305-806, Korea Y.-M. Kim Division of Electron Microscopic Research, Korea Basic Science Institute, Daejeon 305-806, Korea M.-H. Jung Quantum Material Research Team, Korea Basic Science Institute, Daejeon 305-806, Korea Z. Jaglicˇic´ Institute of Mathematics, Physics and Mechanics, Jadranska 19, Ljubljana 1000, Slovenia P. Umek J. Dolinsˇek (&) J. Stefan Institute, University of Ljubljana, Jamova 39, Ljubljana 1000, Slovenia e-mail: jani.dolinsek@ijs.si Introduction The one-dimensional (1D) nanostructures in the form of single-crystalline nanorods and nanowires have attracted considerable interest because of their fasci- nating application as interconnects and building blocks in the nanoscale electronic, optoelectronic, and spin- tronic devices [1–3]. Self-assembled quasi-1D nanorods and nanowires, of typically several 10 nm in diameter and several lm in length, are the smallest-dimension structures that still allow efﬁcient transport of elec- trons. The nanorod- and nanowire form of the material is considered to inﬂuence its physical properties, which depart from the properties of their bulk phases due to quantum effects related to the shape and size [4]. These effects represent a key factor to the ultimate performance and application of the nano-sized material. Among several known materials that can be efﬁ- ciently prepared in the nanorod/nanowire form, man- ganese oxides are of considerable importance in technological applications such as catalysis, molecular sieves and electrodes in rechargeable batteries, owing to their outstanding structural ﬂexibility combined with novel chemical and physical properties [5]. Out of the many polymorphic forms of manganese dioxide (a, b, c and d), which involve different linking of the basic-unit [MnO6] octahedra, a-MnO2 nanowires have been successfully synthesized by the acidiﬁcation–hydrother- mal method [6], whereas their subsequent treatment with ethanol resulted in c-Mn2O3 nanowire bundles. Single-crystalline nanowires of a- and b-MnO2 were also prepared by selected-control hydrothermal method [7] through the oxidation of Mn2+ by S2O82– in the absence of catalysts or templates. A mixture of