Effect of Silanization on the Magnetic and Microwave Absorption Properties of SrFe 12 O 19 Nanostructure Particles MOSTAFA MEHDIPOUR, 1,4 MEHDAD FATHI , 1,5 SINA ARIAE, 2,6 and HOOMAN SHOKROLLAHI 3,7 1.—Magnetic Materials Research Lab, Department of Materials Engineering, Faculty of Mechanical Engineering, University of Tabriz, 5166616471 Tabriz, Iran. 2.—Department of Science and Environment, University of Roskilde, Copenhagen, Denmark. 3.—Electroceramics Group, Materials Science and Engineering Department, Shiraz University of Technology, Shiraz, Iran. 4.—e-mail: Mostafa_mehdipour67@yahoo.com. 5.—e-mail: mehrdadf.t91@gmail.com. 6.—e-mail: Sina.ariaee.mail@gmail.com. 7.—e-mail: shokrollahi@sutech.ac.ir Strontium ferrite nanostructure particles (SrFe 12 O 19 ), which have a ferri- magnetic nature, were synthesized by a co-precipitation process of chloride salts using a sodium hydroxide solution. The resulting precursors were heat- treated in a furnace at 1100°C for 4 h. After cooling in the furnace, the nanostructure particles were silanized using 3-methacryloxypropyltrimethoxy silane molecules. After applying the silane pretreatment to the surface of the nanoparticles, we studied the effects of the most influential silanizing parameters, including the silane concentration and hydrolyzing time, on the magnetic and microwave absorption properties of the samples. The hysteresis loops showed an optimum saturation magnetization of 0.065T for 1h hydrolyzing time at 1.25 wt.% silane concentration; however, no change was detected in the coercivity by varying the two factors. The powders with opti- mum magnetic properties were used to manufacture the samples in order to study the microwave absorption properties. Employing silanized nanostruc- tures resulted in a significant increase in the reflection loss (at the resonance frequency) from  16 dB up to  72 dB. Key words: Magnetic materials, nanostructures, organic compounds, magnetic properties INTRODUCTION Magnetic ceramics, or ferrites, are some of the most important magnetic materials, especially for high-frequency applications. Among these types of magnetic materials, Ba and Sr-ferrites with hexag- onal structures are the two main classes that exhibit hard-magnetic properties. These kinds of ferrites with hexagonal structure (also known as hexaferrites) first emerged in the 1950s. The stron- tium-based hexaferrites are created by a special stacking sequence of close-packed oxygen layers with strontium ions partially substituting for oxy- gen ions at specific places in the unit cell, and the small metallic ions occupying interstitial places. 1–3 Strontium hexaferrite (SrFe 12 O 19 or SrM) with a netoplumbine structure has the unit cell dimensions of a = b = 5.88 A ˚ and c = 23.20 A ˚ . As is required for permanent magnetics, SrM exhibits high coercivity. Other properties of SrM are the large saturation magnetization (72 emu/g), high Curie temperature (450°C), large gyromagnetic effect, and excellent chemical stability and corrosion resistance. 3–6 These ferrite materials are used in magnetic record- ing media, magnetic resonance imaging devices, microwave applications, etc. 7 In the applied fields of hexaferrites, narrow peak absorbtion is significant in some cases, particularly (Received November 8, 2018; accepted May 20, 2019) Mostafa Mehdipour and Mehdad Fathi have contributed equally to this work. Journal of ELECTRONIC MATERIALS https://doi.org/10.1007/s11664-019-07317-0 Ó 2019 The Minerals, Metals & Materials Society