Appl Phys A (2009) 94: 601–606 DOI 10.1007/s00339-008-4890-7 Structure and magnetic properties of Zn 0.9 Co 0.1 O nanorods synthesized by a simple sol–gel method using metal acetylacetonate and poly(vinyl alcohol) Santi Maensiri · Paveena Laokul · Jutharatana Klinkaewnarong · Chunpen Thomas Received: 10 April 2008 / Accepted: 1 September 2008 / Published online: 24 September 2008 © Springer-Verlag 2008 Abstract Room-temperature ferromagnetism was observed in Zn 0.9 Co 0.1 O nanorods with diameters and lengths of ∼100–200 nm and ∼200–1000 nm, respectively. Nanorods were synthesized by a simple sol–gel method using metal acetylacetonate powders of Zn and Co and poly(vinyl al- cohol) gel. The XRD, FT-IR and SAED analyses indicated that the nanorods calcined at 873–1073 K have the pure ZnO wurtzite structure without any significant change in the structure affected by Co substitution. Optical absorption measurements showed absorption bands indicating the pres- ence of Co 2+ in substitution of Zn 2+ . The specific magneti- zation of the nanorods appeared to increase with a decrease in the lattice constant c of the wurtzite unit cell with the highest value being at 873 K calcination temperature. This magnetic behavior is similar to that of Zn 0.9 Co 0.1 O nanopar- ticles prepared by polymerizable precursor method. We sug- gest that this behavior might be related to hexagonal c-axis being favorable direction of magnetization in Co-doped ZnO and the 873 K (energy of 75 meV) being close to the exci- ton/donor binding energy of ZnO. PACS 75.50.Pp · 75.50.Tt · 75.75.+a · 78.40.Fy · 81.07.Bc · 81.10.Dn · 81.20.Fw S. Maensiri ( ) · P. Laokul · C. Thomas Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen, 40002, Thailand e-mail: sanmae@kku.ac.th Fax: +66-43-202374 S. Maensiri · P. Laokul · C. Thomas Integrated Nanotechnology Research Center (INRC), Khon Kaen University, Khon Kaen, 40002, Thailand J. Klinkaewnarong School of Physics, Faculty of Science, Udonthani Rajabhat University, Udonthani, 41000, Thailand 1 Introduction Diluted magnetic semiconductors (DMSs) produced by dop- ing small amount of magnetic impurities in semiconductors have currently attracted much attention as materials for spin- tronic applications [1–3]. Transition metal ion doped ox- ide semiconductors based on ZnO, TiO 2 , SnO 2 , and In 2 O 3 have been investigated extensively. Excellent reviews of re- cent progress on oxide-based DMSs were recently published elsewhere [4, 5]. Unlike the diluted magnetic semiconduc- tors based on III–V or II–VI semiconductors showing fer- romagnetism only at very low temperatures, these oxide- based DMSs exhibit ferromagnetism at higher temperature and even well above room temperature. They are also op- tically transparent enabling them to be promising candi- dates for magneto-opto-electronic applications. The possi- ble mechanisms for an intrinsic origin of the ferromag- netism in these oxide-based DMSs such as carrier-induced [6], double-exchange [7] and a new exchange mechanism involving donor electrons in an impurity [8] have been pro- posed. However, this is still under debate. Among other oxide based DMS, ZnO doped with small amount of Co 2+ (i.e., Zn 1−x Co x O, x = 0.05–0.2) without any modification in the structure have been of the most con- siderable interest. Most studies reported on Co doped ZnO have been made on thin films fabricated either by laser-pulse deposition or sol gel spin coating. However, it is also impor- tant to study ferromagnetic properties in nanocrystalline ma- terials as they will be potentially useful for ferrofluids, mag- netic recording, and biomedical applications. Very few stud- ies on the synthesis and magnetic properties of nanocrys- talline Zn 1−x Co x O DMSs have been reported [9–12]. So far, most of the nanocrystalline Co-doped ZnO DMSs are in the form of micro/nano-particles, and there are only a few reports on the Co-doped ZnO DMSs in the form of