Growing barium hexaferrite (BaFe12O19) thin films

Growing barium hexaferrite (BaFe12O19) thin films using chemical solution deposition Sri Budiawanti and Bambang Soegijono Citation: AIP Conference Proceedings 1729, 020020 (2016); doi: 10.1063/1.4946923 View online: http://dx.doi.org/10.1063/1.4946923 View Table of Contents: http://scitation.aip.org/content/aip/proceeding/aipcp/1729?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Spin-phonon coupling in BaFe12O19 M-type hexaferrite J. Appl. Phys. 116, 244110 (2014); 10.1063/1.4904062 Al doped Ba hexaferrite (BaAlxFe12-xO19) thin films on Pt using metallo-organic decomposition J. Appl. Phys. 111, 07A514 (2012); 10.1063/1.3676604 Tunneling stabilized magnetic force microscopy of BaFe12O19 with a thin film tip Appl. Phys. Lett. 61, 357 (1992); 10.1063/1.107942 The deposition of BaFe12O19 by metalorganic chemical vapor deposition J. Appl. Phys. 71, 6013 (1992); 10.1063/1.350456 Pulsed laser deposition of epitaxial BaFe12O19 thin films J. Appl. Phys. 71, 5107 (1992); 10.1063/1.350614

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Growing Barium Hexaferrite (BaFe12O19) Thin Films Using Chemical Solution Deposition Sri Budiawanti1, 2, a) and Bambang Soegijono3 1

Graduate Program of Materials Science, Department of Physics, FMIPA, Universitas Indonesia, Kampus UI Depok, Indonesia 2 Faculty of Teacher Training and Education, Sebelas Maret University 3 Multiferroic Laboratory, Department of Physics, FMIPA, Universitas Indonesia, Kampus UI Depok, Indonesia a)

Corresponding author: [email protected]

Abstract. Barium hexaferrite (BaFe12O19, or simply known as BaM) thin films has been recognized as a potential candidate for microwave-based devices, magnetic recording media and data storage. To grow BaM thin films, chemical solution deposition is conducted using the aqueous solution of metal nitrates, which involves spin coatings on Si substrates. Furthermore, Thermal Gravimeter Analysis (TGA), X-Ray Diffractometer (XRD), Scanning Electron Microscopy (SEM) and Vibrating Sample Magnetometer (VSM) are applied to evaluate the decomposition behavior, structure, morphology, and magnetic properties of BaM thin films. Additionally, the effects of number of layers variation are also investigated. Finally, magnetic properties analysis indicates the isotropic nature of the films.

INTRODUCTION Barium hexaferrite (BaFe12O19-BaM) is known as a permanent magnetic material. Thin films of barium have been widely used in microwave devices, magnetic recording media and data storage, due to its excellent chemical stability, high mechanical durability, low conduction loss, high saturation magnetization, high coercivity and large uniaxial anisotropy [1-4]. In particular, BaM films are possible to be integrated with piezoelectric films to produce a magnetoelectric coupling between a magnetostrictive and piezoelectric phases [4-6]. Furthermore, synthetic BaM films are possible to be produced by using different techniques, e.g. chemical solution deposition [1-3, 5, 6], radio frequency magnetron sputtering method [7], pulsed laser deposition (PLD) [8], topotactic reactive diffusion process [9] and spray pyrolytic [10]. Among these techniques, chemical solution deposition offers an advantage due to its low capital investment costs, chemical composition control, a good homogeneity and thickness uniformity over a large area, and the ability to use various substrates [11]. The main objective of this research is to grow hexagonal barium ferrite thin films on silicone (Si) substrates. The effect of number of layers variation on the phase formation, morphology, and magnetic properties of the thin films are also the focus of this investigation.

EXPERIMENTAL PROCEDURES Sols are prepared by dissolving barium nitrate Ba(NO3)2 and iron nitrate Fe(NO3)3.9H2O in a mixture of water, glycol and 2-methoxyethanol under stirring at 75 ºC for 3 hours. The concentration of Ba(NO3)2 is set at 0.05 mol/L, while polyvinyl pyrrolidone (PVP, 2 wt.%) is added to the solution to adjust its viscosity. The sols being prepared are stored for 24 hours at an ambient temperature, and then applied as a precursor for the deposition of thin films. The films is later deposited on Si (0 0 1) single crystalline substrates by using a spin coater MTI technology at 3000 rpm for 20 seconds. Prior to the spinning, the substrates are ultrasonically cleaned with distilled water followed by acetone. Next, the deposited films are dried at 80 ºC for 15 minutes. In particular, the deposition and drying processses are repeated for several times. After that, the deposited films are heated in a furnace at 550 ºC for 3 hours

International Symposium on Current Progress in Mathematics and Sciences 2015 (ISCPMS 2015) AIP Conf. Proc. 1729, 020020-1–020020-4; doi: 10.1063/1.4946923 Published by AIP Publishing. 978-0-7354-1376-4/$30.00

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to decompose organic additives (polyvinyl pyrrolidone, ethylene glycol and 2-methoxyethanol) between the successive coatings. Besides, a varied number of layers is deposited and heat-treated at 1000 ºC for 3 hours in the open air. Thermal Gravimeter Analysis (TGA) is then applied to examine the decomposition behavior of dried gel. To investigate the structural properties of films, an X-Ray diffractometer (XRD, Bruker D8 Advance with λ Cu = 1,547 Å) is used. The morphology of the film surface is also determined by using a Field Emission Scanning Electron Microscope (FESEM, FE Inspect F50). Then, a Vibrating Sample Magnetometer (VSM,OxfordV SM1.2H) is applied to analyze the magnetic properties.

RESULTS AND DISCUSSION Figure 1 exhibits films with a varied number the results of TGA over the dried gel. The TGA curves of dried gel are recorded by using a thermogravimetric analyzer within a range of 30 ºC to 800 ºC. During the heat treatment, several other processes such as dehydration, oxidation of the residual organic groups, decomposition and sintering are conducted [12]. Within a range of 33.4 ºC to 183.6 ºC, the weight loss of the dried gel is discovered at approximately 47.97% due to water evaporation a decreased solubility. In the range of 183.6 ºC to 158.9 ºC the weight loss is observed at 20.05%, due to the combustion of the carbon-based content during heat treatment. In addition, a 5.46% weight loss is also observed at range of 358.9 ºC to 589.2 ºC. These weight losses may have occurred due to the decomposition of precursor and released gases, e.g. nitrogen monoxide, nitrogen dioxide, and oxygen. In fact, the TGA curve becomes smoother when the temperature exceeds 700 ºC, which might be indicating the transformation of amorphous phase to the crystalline phase of BaM. The XRD patterns of the layers are exhibited in Fig. 2. For the 3 layers thin films, no well defined BaM peaks are observed in the XRD patterns, except the α-Fe2O3 peak. The XRD pattern of 3 layers film also indicates the amorphous phase. As the number of layer further increases, for instance 5 layers, the BaM phase begins to emerge. With the increasing number of layer, α-Fe2O3 appears in the amorphous matrix. At the 5 and 9 layers films, the αFe2O3 phase still exists. When the number of layers increases, the reflections due to BaFe12O19 are gradually intensified, and the formation of BaFe12O19 phase predominates over α-Fe2O3 phases. It might be indicating that an increase number of layers for Si substrates increases the weight percentage of the compound materials of BaFe12O19. The peaks of BaFe12O19 are displayed in the XRD patterns, therefore reveals that the grains of BaM films are randomly oriented. Then, the unit cell parameters for the films are determined (a = 5.889 Å; b = 5.889 Å; c = 23.243 Å).

FIGURE 1. TGA curve of the BaM dried gel

FIGURE 2. XRD patterns of BaM thin films at a varied number of layers


(a)

(b)

FIGURE 3. FESEM micrographs of the BaM film deposited on Si with a varied number of layers, (a) 5 layers (b) 9 layers

FIGURE 4. Magnetic hysteresis loops in the parallel and perpendicular directions of a 9-layers BaM films

FIGURE 5. Magnetic hysteresis loops of BaM thin films at a varied number of layers

Next, the surface morphology of all films is studied by using FESEM. Figure 3 exhibits FESEM micrographs of the BaM films deposited on Si with a varied number of layers. The rotational speed is maintained at a constant 3000 rpm. In fact, the growth of grains might be caused by a diffusion process in the annealing process as well as in the addition of number of layers. The images show that the films are clearly composed of a relatively uniform distribution throughout the substrates surface. Figure 4 exhibits the hysteresis loop (MH curves) of the thin layers prepared by chemical solution deposition method. Data is taken from alongside the parallel and perpendicular directions of magnetic fields. In particular, a maximum magnetic field applied is found to be 1 T, while coercive fields in the areas of parallel and perpendicular directions indicate the same figure. The Hc parallel is about 0.461 T, while the perpendicular is about 0.453 T. Moreover, the value of Hc are almost equal at either parallel or perpendicular directions, which demonstrating no magnetic anisotropy at the BaM films is deposited by using chemical solution deposition on a Si substrate. This might be caused by a random crystal orientation possessed by the deposited films Fig. 2. In Fig. 6, the magnetic hysteresis loops of Ba-M thin films at a varied number of layers are illustrated. For the 9 layers film, Hc is about 0.461 T, while for the 5 layers film, Hc is about 0.476 T. We also observe an increasing remanent magnetization and decreasing intrinsic coersive with increasing number of layer.

CONCLUSIONS This research has successfully grown barium hexaferrite thin films directly on a silicon substrate by using chemical solution deposition technique. Study on the effect of number of layers showed that an increase number of layers shall gradually intensify the reflections, due to BaFe12O19, but the α-Fe2O3 phase still exists. SEM study showed that films were composed of uniformly distributed grains throughout the substrates. Furthermore, the grains


of BaM films deposited on a Si substrate are found to be randomly oriented. Finally, magnetic properties analysis verified the isotropic nature of the films.

ACKNOWLEDGMENTS This research is financially supported by Graduate research grant 2015 through letter of decree no.1717/UN2.RI2/HKP.05.00/2015 Universitas Indonesia.

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