Available online at www.sciencedirect.com Journal of the European Ceramic Society 30 (2010) 3167–3171 Magnetic properties and remanence analysis in permanently magnetic BaFe 12 O 19 foams Ugur Topal a,∗ , Halil I. Bakan b a TUB ˙ ITAK, UME (National Metrology Institute), P.K. 54, Gebze 41470 - Kocaeli, Turkey b TUB ˙ ITAK, MAM, Material Institute, P.K. 21, Gebze 41470 - Kocaeli, Turkey Received 2 April 2010; received in revised form 4 June 2010; accepted 16 June 2010 Available online 11 July 2010 Abstract In the present study, magnetic properties of barium ferrite foams were investigated. We especially examine the effects of porosity on interparticle interactions and remanence properties of these materials. It was observed that magnets become harder with porosity. On the other hand, saturation magnetization decreases slightly. Existence of porosities increases the strength of demagnetising-like interactions of neighboring particles. © 2010 Elsevier Ltd. All rights reserved. PACS: 61.43.Gt; 81.05.Rm; 75.50.Ww; 75.60.Ej Keywords: Porous materials; Permanent magnets; Exchange coupling; Remanence properties 1. Introduction M-type barium ferrite with hexagonal structure (BaFe 12 O 19 ) is a well known high-performance permanently magnetic mate- rial, due to its large magnetocrystalline anisotropy, high Curie temperature, relatively large magnetization, excellent chemical stability and corrosion resistivity. 1,2 These features make their applications possible in different areas such as permanent mag- nets, microwave devices and perpendicular magnetic recording media. Recently, we have achieved to fabricate hard magnetic barium ferrite having a foamy structure and preliminary results were published elsewhere. 3 These materials seem to find new application areas in industry mainly due to their light weights and possibility of filling the pores by other materials having different physical property, such as semiconducting, superconducting and polymeric materials. That is, hybrid structures can be formed. In the present study, we examine the magnetic properties of barium ferrite foams extensively. We especially focus on understanding the role of porosity on remanence properties. For this purpose, three samples were synthesized at same furnacing conditions but different pore dimensions and concentrations. ∗ Corresponding author. E-mail addresses: ugur.topal@ume.tubitak.gov.tr (U. Topal), Halil.Bakan@mam.gov.tr (H.I. Bakan). Investigation and understanding the strength of intergrain or interparticle exchange couplings has attracted much atten- tion in the field of magnetism in order to interpret magnetic parameters of the materials which show giant magnetoresis- tance, soft or hard magnetic properties, etc. 4–8 For instance, exchange couplings between grains tend to reduce the storage density of magnetic recording media, and hence the isolation of particle is needed. 4 On the other hand, exchange couplings are desired to obtain high-performance permanent magnets. 9,10 In this study, the influence of porosity on interparticle interactions or exchange couplings, which affect the remanence properties, were examined by the use of remanence relationship M D (H ) = M R (H max ) - 2M R (H ), derived by Wohlfarth and holds for noninteracting particles. 11 In this equation, M D (H) is demagnetization remanence and M R (H) is isothermal magnetization remanence. Deviation from this equation is explained by existence of particle interactions. For interacting particles, the equation above was modified by Kelly et al. 12 as δM(H ) = m D (H ) - (1 - 2m R (H )), which gives the sign and the relative strength of the interactions. Here m R (H) and m D (H) are the remanences normalized to the saturation remanence value M R (H max ). 0955-2219/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2010.06.008