Structural, magnetic, optical, and magneto-optical properties of CoFe2O4 thin films fabricated by a chemical approach
Graphical abstract
High quality homogeneous CoFe2O4 thin films have been prepared by cost effective chemical solution approach. After annealing at 500 °C or more, they show inverse spinel structure, saturation magnetization comparable with the bulk crystal value, and overall improvement in their crystalline properties. With increasing annealing temperature, the samples also show overall improvement in their optical and magneto-optical response.
Introduction
Development of electronic and optoelectronic technologies focuses on continuously smaller devices and their feature size, which can show excellent performance improvement and lower power consumption. Generally, this also implies necessary changes to the materials used, or their deposition process. In most cases, fabrication is attuned with high levels of integration that often include ferrite thin films or ferromagnetic composite devices [1,2]. Progress in miniaturization and integration of microwave devices is influenced by the ability to fabricate thin films with high tunability of their physical properties, especially for lower loss. The structure-property correlation of ferrite thin films depends on their composition, preparation conditions, particle size, and morphology. The magnetic properties of ferrite thin films are also strongly dependent on their nanostructure and deposition methods [3,4]. Data storage based on ferromagnetic thin films made a revolutionary impact on paperless technologies, so this area of research has been attracting potential interest due to its applications for even higher storage capacity. Cobalt ferrite has specifically attracted attention because of its strong magneto-crystalline anisotropy and high Curie temperature in several technological applications such as high-density recording media, spin filtering and multiferroics [[5], [6], [7]].
Nanoscale magnetic thin film growth and fabrication have been performed using various methods such as electrodeposition [8], non-aqueous solution [9], sol-gel [10,11], sputtering, molecular beam epitaxy, pulsed laser deposition [12], etc. Recent results in the synthesis of periodic nanoporous cobalt ferrite thin films have exhibited tunable room temperature ferromagnetism and their magnetic properties dependency on crystallite size of the ferrite. Very smooth thin films of nanoferrite materials have also become attractive for research and development because of their potential magneto-optical applications [13]. For many investigations using optical and magneto-optical effects, thin films are known to be homogeneous, continuous, and transparent below bandgap. They are also partially transparent, depending on their thickness, above the bandgap energy. High-quality ferrite thin films are essential for most of the magnetic devices that require low magnetic losses and tailored magnetic properties [14].
Magnetic properties of ferrite films are highly sensitive to crystalline disorder if compared with other metal films, such as permalloy ones. Soft magnetic thin films of cobalt ferrite are employed as high magnetostrictive materials for stress, pressure, and torsion sensors, catalysts or gas/humidity sensors [15], and microactuators [16]. The objective of this work is to synthesize and fabricate high-quality CoFe2O4 crystalline thin films with industry applicable properties using dip-coating into a chemical solution. Their structural, magnetic, optical, and magneto-optical properties have been analyzed by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Vibrating Sample Magnetometry (VSM), Ellipsometry, and Magneto-Optical Kerr Effect (MOKE) spectroscopy.
Section snippets
Experimental details
Used ingredients, Fe(NO3)3.9H2O (99.9%), Co(NO3)2.6H2O, ethylene glycol, and citric acid, were procured by Sigma Aldrich. Stoichiometric amounts of the metal salt precursors Fe(NO3)3.9H2O (2.02 g) and Co(NO3)2.6H2O (0.7275 g) were dissolved in 25 ml of ultrapure water from a Millipore Elix A3-MilliQ system (MilliQ, Germany) to get a clear yellowish-brown colored solution. An aqueous solution of citric acid (6.3 g in 100 ml) was added to the precursor solution under constant magnetic stirring
Methods
X-ray diffraction patterns were recorded under Co Kα irradiation (λ =1.789 Å, 35 kV, 25 mA) using a Bruker D8 Advance diffractometer (Bruker AXS) equipped with a fast position sensitive detector VÅNTEC 1. Measurements were carried out in reflection mode using Bragg-Brentano geometry in the angular range of 3–100°.
SEM micrographs of the annealed thin films were obtained with a Quanta 650 FEG (Thermo Fisher Scientific) scanning electron microscope, operated in the field emission mode under low
Results and discussion
XRD patterns of CoFe2O4 thin films, annealed at temperatures 300 °C, 400 °C, and 500 °C are shown in Fig. 1. The diffraction pattern for the sample annealed at 300 °C exhibits an incomplete crystalline phase as the critical temperature required to fully decompose the precursors incorporated in prepared layers is above 300 °C. However, improvement in the crystalline structure with the increase of annealing temperature is shown from case (a) to case (c) in Fig. 1. The annealed CoFe2O4 films are
Conclusion
Homogeneous high-quality nanocrystalline thin films of CoFe2O4 were fabricated using a cost-effective chemical solution approach based on sol-gel and dip-coating. The films annealed above 500 °C exhibited crystalline phase with inverse spinel structure. The prepared films were ferrimagnetic and increased their saturation magnetization with annealing temperature. In the case of the inverse spinel structure, the alignment is ferrimagnetic (canted spins) at room temperature. The optical
Acknowledgments
The authors acknowledge support from the Postdoc II project opportunity for young researchers Reg. No. CZ.1.07/2.3.00/30.0055, the ERDF in the IT4Innovations national supercomputing center - path to exascale project (CZ. 02.1.01/0.0/0.0/16_013/0001791) within the OPRDE, the MATFUN project (CZ. 02.1.01/0.0/0.0/15_003/0000487), the GAČR18-22102S and the Student Grant Competition of the Czech Ministry of Education, Youth and Sports, SP2018/43 and SP2018/96. The authors acknowledge Prof. Vladimír
References (34)
- et al.
Mater. Res. Bull.
(1995) - et al.
J. Magn. Magn. Mater.
(2002) - et al.
Ceram. Int.
(2009) - et al.
Colloids Surfaces A: Physicochem. Eng. Aspects
(2012) - et al.
Chem. Eng. J.
(2007) - et al.
J. Mag. Mag. Mater.
(1993) - et al.
Phys. Procedia
(2015) - et al.
IEEE
(2005) - et al.
Langmuir
(2013) - et al.
J. Mater. Chem.
(2011)
J. Nanometer
IEEE Trans. Magn.
J. Mater. Chem. C
J. Mater. Sci.
Nano Res.
J. Am. Chem. Soc.
J. Inorg. Organomet. Polym. Mater.
Cited by (19)
Improved photocatalytic performance in Ce<sup>3+</sup> doped CoFe<inf>2</inf>O<inf>4</inf> nanoparticles by modifying structural, optical, and magnetic properties
2024, Materials Science in Semiconductor ProcessingEffect of annealing temperature on phase transitions and photo-Fenton catalytic activity of CoFe<inf>2</inf>O<inf>4</inf> nanopowder
2023, Journal of Physics and Chemistry of SolidsStructural, morphological, and optical properties of Co- substituted Zn<inf>2</inf>SiO<inf>4</inf> nanopowders prepared by a hydrothermal-assisted sol-gel process
2022, Materials Chemistry and PhysicsCitation Excerpt :Transition metal-based materials have attracted much attention thanks to their interesting optical, electrical, structural, and electronic properties [1–5].
Accurate band gap determination of chemically synthesized cobalt ferrite nanoparticles using diffuse reflectance spectroscopy
2021, Advanced Powder TechnologyAn efficient and magnetically recoverable g-C<inf>3</inf>N<inf>4</inf>/ZnS/CoFe<inf>2</inf>O<inf>4</inf> nanocomposite for sustainable photodegradation of organic dye under UV–visible light illumination
2021, Environmental ResearchCitation Excerpt :Cobalt ferrite (CoFe2O4) is an inverse spinel oxide that comprises, large curie temperature, high adsorption capacity, better chemical stability, low toxicity, and moderate magnetization. The CoFe2O4 NPs play a key role in various applications such as cancer treatment (Colombo et al., 2012), supercapacitor (Sankar et al., 2015), photocatalysis (Jing et al., 2016), high-density recording media (Illa et al., 2019), and gas sensors (Khandekar et al., 2014) also. Recently, Kula Kamal Senapati et al. (2012) reported a magnetically separable CoFe2O4/ZnS nanohybrid for the UV-light-driven photodegradation MO dye.