The effect of Mg-Al additive composition on microstructure, magnetic properties, and microwave absorption on BaFe 122x Mg x Al x O 19 (x = 0–0.5) material synthesized from natural iron sand Martha Rianna a , Marhaposan Situmorang a , Candra Kurniawan b , Anggito P. Tetuko b , Eko Arief Setiadi b , Masno Ginting b,⇑ , Perdamean Sebayang b,⇑ a Department of Physics, Universitas Sumatera Utara, Medan 20155, Indonesia b Research Center for Physics, Indonesian Institute of Sciences (LIPI), Tangerang Selatan, Banten 15314, Indonesia article info Article history: Received 12 April 2019 Received in revised form 2 August 2019 Accepted 31 August 2019 Available online 31 August 2019 Keywords: Barium hexaferrite Co-precipitation Magnetic properties Microwave absorber abstract The syntheses of BaFe 122x Mg x Al x O 19 have been successfully carried out at x = 0–0.5 using the co- precipitation method and the precursors of BaCl 2 , MgCl 2 , Al 2 Cl 3 and natural iron sand from Kata Beach, Sumatera Barat-Indonesia. The characterizations were carried out using XRD, FE-SEM, VSM, and VNA. The effect of Mg-Al addition to the barium hexaferrite microstructure resulted in the decreasing of mag- netic properties and the decreasing of microwave absorption. The results of the study obtained was a BaFe 12 O 19 with particle sizes ranging between 28.1 nm and 44.2 nm. The optimum condition was obtained at x = 0.1 with a crystal diameter of 44.2 nm, a magnetic saturation of 44.75 emu g 1 and a magnetic coercivity of 2358 Oe. The maximum reflection loss value is 63.85 dB at a frequency of 10.90 GHz and the micro-wave absorption is 99.99%. Ó 2019 Published by Elsevier B.V. 1. Introduction Barium hexaferrite (BaFe 12 O 19 ), which exhibits a hexagonal structure, has a high coercivity (6700 Oe) [1], a saturation magne- tization of 72 emu g 1 [2], a Curie temperature of 502 °C and wide resonance frequency ranges (S-band, X-band and K-band) [3,4]. The magnetic properties of BaFe 12 O 19 are influenced by the substi- tution of Fe 3+ and Ba 2+ ions. The substitution of M-hexaferrites (M = metal), in microwave technology is needed because the reso- nant frequency of ferromagnetic material able to absorb the micro- wave as a function of frequency and can be controlled by a certain level of ion substitution [5,6]. BaFe 12 O 19 can be substituted with tetravalent, divalent, non-magnetic and magnetic cations, such as: Co, Zn, Ti, Al, Mg, Mn, Ti, Ni [7–14]. The additions of Mg and Al for the doping of barium hexaferrite synthesis are needed to change the hard magnetic to soft magnetic properties and to increase the microwave absorption [12,13]. The synthesis of BaFe 12x Mg x O 19 [14,15] with the addition of Mg obtained an optimum condition of microwave absorption at x=1 with the reflection loss of 24.68 dB at 9.04 GHz. The BaFe 12x Al x O 19 synthesis has been conducted by previous researchers using the addition of Al where an optimum condition was obtained for microwave absorption at x = 2 with a reflection loss of 43 dB at 15.70 GHz [16–21]. Verma et al. [22] reported that BaFe 12 O 19 substitution using the addition of x = 0.1, was the optimum condition (Hc = 2.5 kOe). In addition, Hozeri et al. [23] reported that the magnetic properties decreased due to the addi- tion of doping in barium hexaferrite at x = 0–0.5. Natural iron sand is a potential resource in Indonesia and can be used as a magnet-ferrite raw material. Setiadi et al. (2016) [24] have reported the synthesis of Fe 3 O 4 from the natural iron sands of Sungai Buaya in Deli Serdang, Sumatera Utara-Indonesia using the co-precipitation method. Fe 3 O 4 from natural iron sand offfered several advantages, such as: soft magnetic properties, low prices, and has the ability to increase the micro-wave absorption [25,26]. In this study, Mg-Al will be added and its effect on the microstructure will be discussed, as well as its effect on the mag- netic properties, and the microwave absorption of BaFe 122x Mg x - Al x O 19 x = 0–0.5 material synthesized from natural iron sand at a constant calcination temperature of 1050 °C. This results is expected to be one of the innovation and can be applied in the defense and military industries. https://doi.org/10.1016/j.matlet.2019.126612 0167-577X/Ó 2019 Published by Elsevier B.V. ⇑ Corresponding authors. E-mail addresses: masno.ginting@gmail.com, masno.ginting@lipi.go.id (M. Gint- ing), perdamean.sebayang@lipi.go.id (P. Sebayang). Materials Letters 256 (2019) 126612 Contents lists available at ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/mlblue