Nanoscale PAPER Cite this: Nanoscale, 2017, 9, 7858 Received 2nd March 2017, Accepted 14th May 2017 DOI: 10.1039/c7nr01541k rsc.li/nanoscale Epitaxial magnetite nanorods with enhanced room temperature magnetic anisotropy† Sayan Chandra,‡ a Raja Das,‡ b Vijaysankar Kalappattil, b Tatiana Eggers, b Catalin Harnagea, a Riad Nechache, c Manh-Huong Phan,* b Federico Rosei * a and Hariharan Srikanth * b Nanostructured magnetic materials with well-defined magnetic anisotropy are very promising as building blocks in spintronic devices that operate at room temperature. Here we demonstrate the epitaxial growth of highly oriented Fe 3 O 4 nanorods on a SrTiO 3 substrate by hydrothermal synthesis without the use of a seed layer. The epitaxial nanorods showed biaxial magnetic anisotropy with an order of magnitude differ- ence between the anisotropy field values of the easy and hard axes. Using a combination of conventional magnetometry, transverse susceptibility, magnetic force microscopy (MFM) and magneto-optic Kerr effect (MOKE) measurements, we investigate magnetic behavior such as temperature dependent magnetization and anisotropy, along with room temperature magnetic domain formation and its switch- ing. The interplay of epitaxy and enhanced magnetic anisotropy at room temperature, with respect to randomly oriented powder Fe 3 O 4 nanorods, is discussed. The results obtained identify epitaxial nanorods as useful materials for magnetic data storage and spintronic devices that necessitate tunable anisotropic properties with sharp magnetic switching phenomena. 1 Introduction Magnetic anisotropy is the key property that determines the operational performance of any magnetoresistance-based data storage technology in the market. 1,2 Over the past two decades, research in this area has flourished, investigating both material development and the device engineering standpoint. It has been shown that heteroepitaxy of multicomponent, mul- tilayered structures is essential for superior performance of such devices in comparison to polycrystalline multilayers; especially in technologies which involve the tunneling mech- anism of magnetic spin or electrons. 3–7 In this regard, all oxide functional thin film devices have shown promising results by exploiting exotic physical phenomena such as charge- or strain-driven magnetoelectric coupling, spin polariz- ation-based filtering, etc. 8–10 While a number of candidate fer- roelectric/multiferroic materials have been identified including BiFeO 3 , BaTiO 3 , PZT, Bi 2 FeCrO 6 etc., there are very few oxide magnetic materials which can be grown epitaxially for room temperature operation. 11,12 Any device or electrical component generates heat during operation and therefore the material of choice should sustain its properties at least 60–80 K above room temperature. The most widely used magnetic oxide is La 0.7 Sr 0.3 MnO 3 (LSMO), which can be grown in various mor- phologies while maintaining epitaxy. However, the strongest drawback of LSMO is its magnetic Curie temperature (T C ) of 370 K which is highly malleable due to effects from oxygen off- stoichiometry or substrate induced strain. 13 This prompts us to identify an alternative material with high magnetic T C and most importantly, a material that can be grown epitaxially on cubic perovskites. Magnetite, or Fe 3 O 4 , exhibits a T C of 850 K and has been successfully grown epitaxially on a number of cubic perovskite substrates such as MgO, 14 SrTiO 3 , etc. 15 Contrary to other inverse spinel ferrites, since Fe 3 O 4 is a binary oxide, compli- cations arising due to cationic off-stoichiometry, e.g. CoFe 2 O 4 16,17 or NiFe 2 O 4 , 18 can be avoided. In addition, Fe 3 O 4 is a promising material for room temperature device appli- cations due to its full spin polarization and half metallic be- havior. 19,20 Aside from the wide application of Fe 3 O 4 nano- particles in the fields of biological and medical physics, 21–23 the large value of spin Seebeck voltage reported recently in Fe 3 O 4 /Pt multilayer structures 24 makes magnetite a promising material in a variety of technological applications. 25–27 † Electronic supplementary information (ESI) available. See DOI: 10.1039/ c7nr01541k ‡ These authors contributed equally to this work. a CentrevbÉnergie, Materiaux et Télécommunications, INRS, 1650 Boulevard Lionel Boulet, Varennes, QC J3X 1S2, Canada. E-mail: rosei@emt.inrs.ca b Department of Physics, University of South Florida, FL 33620, USA. E-mail: phan@usf.edu, sharihar@usf.edu c Département de Génie Electrique, Ecole de technologie supérieure, 1100 rue Notre-Dame Ouest, Montréal, QC H3C 1K3, Canada 7858 | Nanoscale, 2017, 9, 7858–7867 This journal is © The Royal Society of Chemistry 2017 Published on 16 May 2017. Downloaded by Institut nationale de la recherche scientifique (INRS) on 14/06/2017 14:08:03. View Article Online View Journal | View Issue