Journal of Magnetism and Magnetic Materials 234 (2001) 255–260 Synthesis of Cu-modified Co 2 Z hexaferrite with planar structure by a citrate precursor method Xiaohui Wang a, *, Tianling Ren b , Longtu Li a , Zhilun Gui a , Shuiyuan Su a , Zhenxing Yue a , Ji Zhou a a State Key Lab of New Ceramics and Fine Processing, Department of Materials Science and Engineering, Tsinghua University, Beijing, 100084, People’s Republic of China b Institute of Microelectronics, Tsinghua University, Beijing, 100084, People’s Republic of China Received 12 December 2000; received in revised form 23 April 2001 Abstract Co 2 Z hexaferrite is a planar anisotropic iron oxide which can present high values of permeability at high frequency. In this paper, Cu-modified Co 2 Z hexaferrites powders were synthesized at a low temperature using a citrate precursor method. The formation of Z-type phases was characterized by X-ray diffraction and magnetization measurements. It is found that phase formation temperature and sintering temperature were influenced directly by the content of copper. The effects of Cu-substitution on the microstructure and high frequency properties of the ceramics have been investigated. r 2001 Elsevier Science B.V. All rights reserved. Keywords: Cu-substitution; Z-type hexaferrite; High frequency property; Low-temperature sintering; Citrate precursor method 1. Introduction Among the planar hexagonal ferrites discovered between 1952 and 1956 by Philips were Y ferrite (Ba 2 M 2 Fe 12 O 22 ), W ferrite (BaM 2 Fe 16 O 27 ) and Z ferrite (Ba 3 M 2 Fe 24 O 41 )[1,2]. The most important one of them is Co 2 Z (M=cobalt (II)), which has a much higher permeability and ferromagnetic resonance up to 1.5–3.4 GHz and a high thermal stability due to its high Curie point of 4001C [3]. This makes it very useful in high frequency inductor and uhf communication applications [4]. However, the formation temperature of Co 2 Z phase is higher than 12501C because of its complex structure, and it is difficult to be densified below 12701C using a classical ceramic method [5]. How to lower the phase formation temperature as well as sintering temperature of Co 2 Z ferrite remains a problem till now. To our knowledge, few investigations on the structure and magnetic behavior of Cu-modified Co 2 Z have been carried out. Considering the similar ion radii of Cu and Co and the low melting point of CuO, partial substitution of Co with Cu ions in Ba 3 Co 2 Fe 24 O 41 ferrites is expected to lower the sintering temperature just like the copper in the NiZn ferrite system [6,7]. In this work, Ba 3 Co 2x Cu x Fe 24 O 41 compounds were synthesized by a citrate precursor method. The advantage of this method is to improve the *Corresponding author. Tel.: +86-10-627-84579; fax: +86- 10-627-81346. E-mail address: wxh@tsinghua.edu.cn (X. Wang). 0304-8853/01/$ - see front matter r 2001 Elsevier Science B.V. All rights reserved. PII:S0304-8853(01)00376-6