RESEARCH Microwave absorption properties of nanostructure composite particles based on SrFe 12 O 19 Mehdad Fathi 1 & Mostafa Mehdipour 1 & Hooman Shokrollahi 2 Received: 29 November 2018 /Revised: 24 May 2019 /Accepted: 14 October 2019 # Australian Ceramic Society 2020 Abstract This paper studies the magnetic and absorption properties of ferrites based on SrFe 12 O 19 , which were synthesized by the co- precipitation method. The microstructural, structural, loss, and magnetic properties were measured by X-ray diffractometry, field emission scanning electron spectroscopy, network analysis, and vibrating-sample magnetometry, respectively. For the SrFe 12 O 19 / ZnFe 2 O 4 , the hysteresis loops showed a decreasing in coercivity from 2.8 kOe to 0.03 kOe by increasing ratio of soft/hard (S/h) and decreasing in saturation magnetization from 0.7 kg to 0.01 kg by increasing it. These effects were also observed for nanostructure composite particles of SrFe 12 O 19 /NiFe 2 O 4 except for increasing of saturation magnetization by increasing the S/h. The effects of kind and amount of soft phase on microwave absorption properties were also estimated in the X-band (8 GHz to 12 GHz). The maximum reflection loss of the nanostructure composite particles reached to -30 dB at 9.8 GHz for SrFe 12 O 19 / NiFe 2 O 4 , making it suitable for application in radar-absorbing materials. Keywords Nanostructure composite particles . Co-precipitation . Magnetic properties . Microwave Introduction Among recently years, there is a going up for interest in mi- crowave absorbing materials because of their civil applica- tions such as stealth defense system, microwave interference protection, and microwave darkroom. Freshly improvements in microwave absorber technology have been coming from materials that can effectively descend the reflection of electro- magnetic signals on a side and have perfect physical proper- ties and lower production price on the other side [1–3]. A lot of studies has been carried out to produce new mi- crowave absorbing materials with high magnetic and electric loss. Ferrites are good microwave absorbing materials because of their high specific resistance, large electrical resistivity, no- ticeable flexibility, mixing the magnetic properties and ease of production, low cost, low density, and high magnetic loss. Among these materials, Sr-based ferrites are of great interest due to their typical ferromagnetic characteristic and potential application in microwave absorption. Some ferrite particles, including composite of SrFe 12 O 19 /NiFe 2 O 4 and SrFe 12 O 19 / ZnFe 2 O 4 , have been prepared in this work [4–7]. For synthesizing of ferrites, different kinds of methods have been utilized. From these methods, we can relate to co- precipitation method. This process is started by adding a mixture solution containing chloride of cathion (Fe, Sr, and Zn) dropsies into a NaOH/Na 2 CO 3 solution [8–10]. Carbonate or nitrate of cathions can also be utilized instead of chloride of cathions to synthesis hexaferrites [ 11, 12]. To continue, heat treatment makes the process growing, and hexaferrite particles can crystallize completely with hexagonal pyramidal or plate-like shape after cooling in the furnace [ 13, 14]. Similar works were obtained by Tyagi et al. for SrFe 11.2 Zn .8 O 19 [ 15] and SrFe 11 Ni .5 Zn .5 O 19 [ 16]. As relation to the articles in this field, this investigation deals with the synthesis of nanostructure composite particles of SrFe 12 O 19 /ZnFe 2 O 4 and SrFe 12 O 19 /NiFe 2 O 4 by a co- precipitation method. This method is a low-cost technique suitable for mass production compared with other methods [17]. The microwave absorption properties for nanostructure composite particles were studied by reflection loss plots from VNA measurement, and effects of kind and amount of soft phase have been studied. * Mostafa Mehdipour mostafa_mehdipour67@yahoo.com 1 Magnetic Materials Research Lab, Department of Materials Engineering, Faculty of Mechanical Engineering, University of Tabriz, Tabriz, Iran 2 Electroceramics Group, Materials Science and Engineering Department, Shiraz University of Technology, Shiraz, Iran Journal of the Australian Ceramic Society https://doi.org/10.1007/s41779-019-00414-7