Grouping trends of magnetic permeability components in their parallel evolution with microstructure in Ni 0.3 Zn 0.7 Fe 2 O 4 Idza Riati Ibrahim n , Mansor Hashim, Rodziah Nazlan, Ismayadi Ismail, Wan Norailiana Wan Ab Rahman, Nor Hapishah Abdullah, Fadzidah Mohd Idris, Mohd Shamsul Ezzad Shafie, Muhammad Misbah Muhamad Zulkimi Materials Synthesis and Characterization Laboratory, Institute of Advanced Technology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia article info Article history: Received 1 August 2013 Received in revised form 4 December 2013 Accepted 7 December 2013 Available online 21 December 2013 Keywords: Ni–Zn ferrite Complex permeability Microstructure Magnetic properties Sintering abstract Ni–Zn ferrite, Ni 0.3 Zn 0.7 Fe 2 O 4 , with a wide variation of grain sizes has been prepared via high energy ball milling through two different sintering routes: multi-sample sintering and single-sample sintering. The parallel relationships between evolving microstructural properties and AC magnetic response para- meters were investigated using a FEI Nova NanoSEM 50 series and an Agilent Model HP4291B Impedance/Material Analyzer respectively. SEM micrographs showed larger grain size as the sintering temperature increased, consequently increasing the number of multi-domain grains. The AC magnetic response parameters belong to three groups with strongly, moderately and weakly ferromagnetic behavior respectively. Single-sample sintering and multi-sample sintering evolution yield quite similar permeability-grain size relationship trends. The permeability from both sintering routes is influenced by several factors which are degree of crystallinity, dominant magnetization process (ease of domain walls movement in multi-domain grains or spin rotation in single-domain grains) and large enough grain size which surpasses the critical grain size for transition from single-domain to multi-domain grains. & 2013 Elsevier B.V. All rights reserved. 1. Introduction Ni–Zn ferrites are useful for many applications in electromag- netic devices in the radio frequency region due to its important characteristics such as high magnetic permeability, high resistivity, mechanical toughness and chemical stability. The variation of characteristics and performance of ferrites are strongly exhibited through their microstructural variation [1–6]. One of the most crucial magnetic properties for many ferrite applications is the frequency dependence of the complex permeability. In the past, microstructural dependence of magnetic properties for polycrys- talline Ni–Zn ferrites having micron grain size has been widely studied. Various magnetic properties show strong grain size dependence on correlating grain size and permeability of ferrites [6]. The effect of grain size on the initial permeability is more complex in nickel–zinc ferrites. When the average grain size becomes greater than about 15 μm and the percentage of grains with included pores becomes about 50%, the initial permeability reaches a maximum and then begins to decrease [6–8]. The presence of pores in the interior of the grains limits the movement of domain walls. Pores and other imperfections would appear to pin domain walls especially inside of the grain, therefore reducing the permeability value [6–8]. Nowadays, research on magnetic materials with the nano/submicron scale has been a field of intense study, due to the novel properties shown by particles located in the transition region between the isolated atoms and bulk solids [9]. Their novel properties make them attractive, both from the scientific knowledge of understanding their properties and the technological importance of enhancing the performance of the present materials. However a systematic development of microstructures having grain sizes from several nanometers up to microns, with the parallel evolving magnetic properties closely observed, has yet to be undertaken. Hence, in this paper, we report the results of an attempt to experimentally track and explain the relationship between magnetic permeability and microstructure as they evolved in parallel from unusually low sintering tempera- ture to somewhat high sintering temperature. The results raise the possibility that ferrites could be engineered into desired applica- tions with a particular magnetic response by an appropriate choice of microstructural parameters. 2. Materials and method Briefly, the entire experimental work covered two sintering routes, A and B. Route-A samples went through a multi-sample Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jmmm Journal of Magnetism and Magnetic Materials 0304-8853/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jmmm.2013.12.024 n Corresponding author. Tel.: þ60 126726643. E-mail address: idza411@gmail.com (I.R. Ibrahim). Journal of Magnetism and Magnetic Materials 355 (2014) 265–275