The effect of heat treatment temperature on the microstructure and magnetic properties of Ba 2 Co 2 Fe 12 O 22 (Co 2 Y) prepared by sol–gel method Nimai Chand Pramanik a, ⁎ , Tatsuo Fujii b , Makoto Nakanishi b , Jun Takada b , Sang II Seok a a Advanced Materials Division, Korea Research Institute of Chemical Technology, P.O. Box. 107, Daejeon 305-600, South Korea b Department of Applied Chemistry, Faculty of Engineering, Okayama University, Okayama 700-8530, Japan Received 16 August 2005; accepted 26 January 2006 Available online 17 February 2006 Abstract Ferroxplana type hexagonal ferrite with composition Ba 2 Co 2 Fe 12 O 22 (Co 2 Y) was prepared by polymeric sol–gel method from the aqueous solution of their corresponding metal salts. All the samples were characterized by using X-ray diffraction and scanning electron microscopic technique. The formation and the microstructure of the Ba 2 Co 2 Fe 12 O 22 was studied as a function of heat treatment temperature and it was observed that well defined hexagonal plate-like fine particles with particle sizes between 130 and 400 nm were formed at relatively lower temperature (900 °C) as compared to conventional solid state reaction method (1100 °C). Magnetic properties of the samples were also studied as a function of heat treatment temperature and it showed large saturation magnetization (M s ) ranging from 30.9 to 47.6emu/g and a wide range of coercivity (130∼1566 Oe) depending on the heat treatment temperature. The very high saturation magnetization at relatively lower temperature (say 800°C) arises due to the presence of several high magnetic impurities, such as BaFe 12 O 19 and CoFe 2 O 4 . The saturation magnetization increases with increasing heat treatment temperature above 900°C, while the coercivity showed a reversed order. © 2006 Elsevier B.V. All rights reserved. Keywords: Hexagonal ferrite; Sol–gel synthesis; X-ray diffraction; Magnetic properties 1. Introduction Hexagonal ferrite materials with planar structure have received much attention due to their variety of applications in electronic and telecommunication technology [1–3]. These ma- terials exhibited very high specific resistance and remarkable flexibility in tailoring the magnetic properties, which make these materials the ideal choice for various applications [4]. It is indeed to mention here that due to rapid progress of modern information and telecommunication technology, the operational frequencies of the devices is moving very fast from megahertz (MHz) to very high frequency (GHz) region. To meet the demand of the electronic industries, several soft magnetic ma- terials have been studied [1] and it was found that Ba 3 Co 2 Fe 24 O 41 (Co 2 Z) and Ba 2 Co 2 Fe 12 O 22 (Co 2 Y) hexagonal ferrite materials with planar magnetic structure have much higher cut-off frequency than that of the conventional spinel ferrites and exhibited excellent magnetic properties in very high frequency (VHF) and ultra high frequency (UHF) region [5– 7]. Very few works have been reported so far for the preparation of Z-type and Y-type hexaferrites by solid state reaction method [8,9] due to complexity in their structures and high sintering temperature, although the Co 2 Y hexaferrites exhibited relative- ly simpler structure and stronger magnetic planer anisotropy. To our knowledge, very few investigations have been carried out so far for the preparation of Co 2 Y hexaferrite fine powders by wet chemical method [10]. But, the formation and crystallization process of Co 2 Y as a function of temperature was not described any where. In addition, recently sol–gel method has been found to be a very suitable method for the preparation of multi- component oxide materials at relatively lower temperatures. The major advantages of the method are not only to reduce the product formation temperature but also have good control over its homogeneity and their microstructures. Therefore, in this report, we describe the preparation of novel Co 2 Y type hexaferrite (Ba 2 Co 2 Fe 12 O 22 ) by sol–gel method and study of Materials Letters 60 (2006) 2718 – 2722 www.elsevier.com/locate/matlet ⁎ Corresponding author. Tel.: +82 42 860 7326; fax: +82 42 861 4245. E-mail address: ncpramanik@rediffmail.com (N. Chand Pramanik). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.01.077