Room temperature ferromagnetism in epitaxial In 2 O 3 films with embedded nano-sized Fe 3 O 4 columns† Qiang Li, a Lin Wei, b Yanru Xie, a Tie Zhou, a Guoxiang Hu, a Shishen Yan, a Jun Jiao, c Yanxue Chen, * a Guolei Liu a and Liangmo Mei a Epitaxial In 2 O 3 films with embedded Fe 3 O 4 oriented nanocolumns were deposited by pulsed laser deposition (PLD) on Y-stabilized ZrO 2 (111) substrates. The resulting films show ferromagnetism at room temperature with strong magnetic anisotropy, which can be attributed to the presence of Fe 3 O 4 nanocolumns. Magnetotransport measurements demonstrate a transition from negative magnetoresistance to positive magnetoresistance as the measuring temperature increases. Quantitative coincidence between the anomalous Hall resistivity as a function of the magnetic field and the magnetic hysteresis loop is observed at room temperature, indicating the spin polarization nature of carriers. Introduction Diluted magnetic semiconductors (DMSs) have attracted signif- icant attention in recent years due to their potential applications in novel spintronic devices. 1 Recently, there has been an increasing amount of evidence that the doped transition metal ions could aggregate to form magnetic nanocrystals embedded in the host paramagnetic matrix, depending on the growth parameters and transition metal dopant concentration. Such aggregation has been found in GeMn, 2 (Zn,Cr)Te, 3 (Ga,N)Fe 4,5 and (Fe,N)TiO 2 . 6 The semiconductor nanostructures with self-organized Ge 1x Mn x nanocolumns show high-Curie- temperature ferromagnetism with obvious magnetocrystalline anisotropy, giant positive magnetoresistance (MR) and a pronounced anomalous Hall effect. 2 It has been demonstrated that the embedded magnetic nanocrystals may lead to a robust ferromagnetism and spin polarization of the carriers in the whole semiconductor lms. 2,7 These nanocomposites have excellent compatibility with semiconductor device structures and show strong magnetotransport and magneto-optical effects, opening the route for new multifunctional nanosystems relevant to spintronics, nanoelectronics, photonics, and plasmonics. 7,8 Iron oxide nanoparticles such as Fe 3 O 4 and g-Fe 2 O 3 are the most intensively studied magnetic nanoparticles, which can be applied in a variety of areas, such as recording media 9 and biomedical science, 10 owing to their high Curie temperatures, high saturation magnetizations and nearly 100% spin polari- zation. In 2 O 3 is an important wide band gap oxide and has wide applications as a transparent electrode in optoelectronics, e.g., solar cells, display devices, etc. It is expected that nanosized clusters of iron oxide dispersed in the matrix of In 2 O 3 would introduce ferromagnetism and then polarize spins of carriers in the material 11 serving as new multifunctional spintronic mate- rials. However, the control over the magnetic nanocrystals formation in the nanoassembly processes is still challenging. 12 Until now, there have been few reports on In 2 O 3 containing magnetic nanocrystals, 13,14 compared with extensive studies on transition-metal-doped In 2 O 3 DMSs. 15–21 In this paper, we report epitaxial In 2 O 3 lms with embedded Fe 3 O 4 oriented nano- columns deposited by pulsed laser deposition (PLD) on (111) Y- stabilized ZrO 2 (YSZ) substrates. The nanocomposite lms show a strong perpendicular magnetic anisotropy with an out of plane easy axis. A pronounced anomalous Hall effect (AHE) matching quantitatively with the magnetic hysteresis loop has been observed indicating spin polarization of the electrons. The room temperature magnetism is also conrmed by the magneto-optic Kerr hysteresis loop. These results indicate that this novel nanocomposite material is very promising for future spintronics applications. Experimental Synthesis of epitaxial In 2 O 3 lms with embedded oriented Fe 3 O 4 nanocolumns The epitaxial In 2 O 3 lms with embedded oriented Fe 3 O 4 nanocolumns were deposited on YSZ (111) by a PLD technique under a base pressure of 1.0  10 5 Pa. To promote the a School of Physics and State Key Laboratory of Crystal Materials, Shandong University, Jinan, 250100, P. R. China. E-mail: cyx@sdu.edu.cn; Fax: +86 531 88362812; Tel: +86 531 88362812 b School of Information Science and Engineering, Shandong University, Jinan, 250100, P. R. China c Department of Mechanical & Materials Engineering, Department of Physics, Portland State University, Post Office Box 751, Portland, Oregon 97207-0751, USA † Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr34188g Cite this: Nanoscale, 2013, 5, 2713 Received 19th December 2012 Accepted 29th January 2013 DOI: 10.1039/c3nr34188g www.rsc.org/nanoscale This journal is ª The Royal Society of Chemistry 2013 Nanoscale, 2013, 5, 2713–2717 | 2713 Nanoscale PAPER