Structure and physical properties of Fe 6 O 8 /ba Fe 6 O 11 nanostructure Mahmoud Naseri n , Rahmat Ghasemi Department of Physics, Faculty of Science, Malayer University, Malayer, Iran article info Article history: Received 17 October 2015 Received in revised form 5 December 2015 Accepted 8 January 2016 Available online 9 January 2016 Keywords: Nanostructure UV–vis absorption Magnetic properties EPR spectroscopy abstract The thermal treatment method was employed to prepare barium hexaferrite (Fe 6 O 8 /Ba Fe 6 O 11 ) na- nostructure. This method was attempted to achieve higher homogeneity of the final product. Specimens of barium hexaferrite nanostructure were characterized by various experimental techniques including X-ray diffraction (XRD), high resolution Field emission scanning electron microscope (FESEM) and Fourier transform infrared spectroscopy (FT-IR). X-ray diffraction results showed that there was no crystallinity in the predecessor and it had still amorphous phase. The formations of crystalline phases of barium hexaferrite nanostructures started from 673 to 973 K and the final products had different crystallite sizes ranging from 29 to 48 nm. The chemical analysis of the barium hexaferrite nanostructures was performed by energy dispersion X-ray analysis (EDXA), demonstrated that the barium hexaferrite nanostructures contained the elements of Ba, Fe, and O. The effect of calcination temperature on band gap energy was studied by UV–vis absorption spectra disclosed when calcination temperature increased, the appraised band gap energy values of the BaFe 12 O 19 nanostructures decreased. The formed nanostructures exhibited ferromagnetic behaviors which were confirmed by using a vibrating sample magnetometer (VSM). The technique of the Electron paramagnetic resonance (EPR) spectroscopy was carried out at 300 K on the calcined specimens that exhibited the variation of the line-shapes of the spectra of with calcination temperature. & 2016 Published by Elsevier B.V. 1. Introduction Hexagonal ferrites are attracting significant interest due to their extensive applications, ranging from fundamental research to industrial use. They possess unique combination of desirable properties such as low production cost, high saturation magneti- zation (M s ¼ 72 emu/g), high coercivity (H c ¼ 6700 Oe), magneto- crystalline anisotropy along c-axis (H a ¼ 1.7 T), chemically stable, high electrical resistivity and corrosion resistant [1,2]. Among the hexagonal ferrites, M-type magnetoplumbite hexaferrite with general formula MO・6Fe 2 O 3 , where M represents a divalent ions such as Ba 2 þ , Sr 2 þ , or Pb 2 þ , has received significant attention in recent years [3]. The M-type magnetoplumbite hexaferrite crys- tallizes in a hexagonal structure with 64 ions per unit cell on 11 different symmetry sites (P63/mmc space group) and easy mag- netization along c-axis [4]. The structure of M-type hexagonal is stacked alternatively by spinel (S ¼ Fe 6 O 8 2 þ ) and hexagonal (R ¼ MFe 6 O 11 2 À ) layers as the MFe 12 O 19 unit cell is a combination of two structural blocks aligned in the direction of hexagonal c- axis RSR*S* (* indicates the180° rotation of the structural block with respect to the c-axis) [5]. The O 2 À ions exist as close-packed layers, with M 2 þ substituting for an O 2 À in the hexagonal layer and the 24 Fe 3 þ atoms are distributed over five distinct sites: three octahedral sites (12k, 2a and 4f 2 ), one tetrahedral (4f 1 ) site and one hexahedral (trigonal bipyramidal) site (2b) [4]. Among the M-type magnetoplumbite hexaferrite compounds, ferromagnetic barium hexaferrite (BaFe 12 O 19 ) nanostructures have been ex- tensively studied due to it is widely used in fabrication of com- puter data storage, high-density perpendicular magnetic and magneto-optic recording, magnetic fluids and certain microwave devices [6,7]. There are several nonconventional techniques in order to achieve high quality metal oxide nanoparticles which have been used or are under development for preparing ultrafine nanostructures [8–20]. Numerous factors and various precipitation agents were utilized to synthesis magnetic metal oxide nano- crystals with specific structures. On the whole, all these methods require two basic production operations: mixing of initial com- ponents either mechanically or chemically, and a subsequent heat treatment of the obtained mixture: the temperature usually near to 1400 °C [21]. Therefore, the formations of BaFe 12 O 19 nanos- tructure at lower than 1400 °C is an advantage for the preparation of barium ferrite. Because of the annealing at high temperatures, the grain size of the barium ferrite increases, which limits the possibilities of obtaining ultrafine particles for the desired appli- cations, especially basic research. On the other hand, it is reported Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jmmm Journal of Magnetism and Magnetic Materials http://dx.doi.org/10.1016/j.jmmm.2016.01.019 0304-8853/& 2016 Published by Elsevier B.V. n Corresponding author. E-mail addresses: mahmoud.naseri55@gmail.com (M. Naseri), m.naseri@malayeru.ac.ir (R. Ghasemi). Journal of Magnetism and Magnetic Materials 406 (2016) 200–206