Synthesis and magnetic properties of zinc ferrite from mechanochemical and thermal treatments of Zn /Fe 3 O 4 mixtures P.M. Botta a, *, P.G. Bercoff b , E.F. Aglietti c , H.R. Bertorello b , J.M. Porto Lo ´pez a a Instituto de Investigaciones en Ciencia y Tecnologı ´a de Materiales, INTEMA, Av. J.B. Justo 4302, B7608FDQ Mar del Plata, Argentina b Grupo de Ciencia de Materiales, FaMAF (UNC), M. Allende s/n, Ciudad Universitaria (5000) Co ´rdoba, Argentina c Centro de Tecnologı ´a de Recursos Minerales y Cera ´mica, CETMIC, Camino P. Centenario y 506, 1897 M.B. Gonnet, Argentina Received 1 October 2002; received in revised form 8 May 2003 Abstract The preparation of ZnFe 2 O 4 from mechanochemically activated reactive mixtures Zn  /Fe 3 O 4 is studied. The physicochemical and structural evolution of the system is analyzed by X-ray diffraction, vibrating sample magnetometry, differential thermal analysis and scanning electron microscopy. The activated mixtures reacted towards the formation of ZnFe 2 O 4 at lower temperatures than the non-activated ones. In addition, thermal treatments as a function of time revealed a non-expected magnetic behavior of some mixtures. In order to interpret this observation, a qualitative diffusional reaction model is proposed. # 2003 Elsevier B.V. All rights reserved. Keywords: Magnetic materials; Ferrites; Mechanochemistry; Mechanical activation 1. Introduction Soft magnetic ferrites with spinel structure are mate- rials with a large variety of applications in electronic and telecommunication industries [1,2]. Spinel ferrites ex- hibit a wide range of magnetic properties, according to the variable cation distribution in the crystalline struc- ture and the processing conditions employed [1,3]. In the last decade, high-energy ball-milling or me- chanochemical activation has become an increasingly useful technique for synthesizing all kinds of materials [4  /6]. Depending on the system and the activation conditions, this processing method may produce a solid-state reaction during the treatment at room temperature [7,8] or induce significant structural changes that can reduce the temperature needed to carry out certain reactions [9,10]. The products obtained by this technique often present a defective crystalline structure and many of them are metastable phases. Conventionally prepared franklinite (ZnFe 2 O 4 ) is a normal spinel with tetrahedral sites occupied by Zn 2 ions and octahedral sites occupied by Fe 3 ions. The conventional route to synthesize franklinite involves a long thermal treatment of a mixture of ZnO and Fe 2 O 3 at 1200 K. The obtained material has structural and microstructural features that are critical for its final properties; besides, it is difficult to control them due to the severe processing conditions. Therefore, the devel- opment of alternative processing routes is a very important aspect in the synthesis of this ferrite. The mechanochemical activation of reactive mixtures appears as a method to carry out the solid-state reaction in much more convenient conditions than those required by the traditional technique. In this work, a new route for synthesizing ZnFe 2 O 4 starting from Zn  /Fe 3 O 4 mixtures is proposed, analyzing the effects of the mechanical and thermal treatments on the reaction evolution and the nature and magnetic properties of the obtained products. * Corresponding author. Tel.:  /54-223-481-6600; fax:  /54-223- 481-0046. E-mail address: pbotta@fi.mdp.edu.ar (P.M. Botta). Materials and Engineering A360 (2003) 146  /152 www.elsevier.com/locate/msea 0921-5093/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0921-5093(03)00412-X