Sol–gel hydrothermal synthesis of strontium hexaferrite nanoparticles and the relation between their crystal structure and high coercivity properties

Abstract

Hard magnetic strontium hexaferrite SrFe 12 O 19 nanoparticles were synthesized by the sol–gel hydrothermal method. The factors affecting the synthesized process, such as the mole proportion of the reactants, pH, temperature, the hydrothermal conditions and the calcination process, have been investigated. The crystal structures of these materials were refined by Rietveld method. The obtained materials have single crystal phase, equal nano-size, plate shape and high anisotropy. The high magnetic coercivity of 6.3 kOe with the magnetization at 11.1 kOe of 66 emu g −1 at room temperature was observed for the strontium hexaferrite nanoparticles. For other nanoparticles (SrLn x Fe 12-x O 19 and SrFe 12 O 19/CoFe 2 O 4) synthesized on the basis of SrFe 12 O 19 the complex completion of the crystal structure distortion and the interaction between magnetic phases were observed.

Influence of pH Adjustment Parameter for Sol–Gel Modification on Structural, Microstructure, and Magnetic Properties of Nanocrystalline Strontium Ferrite

“…In order to achieve highly homogeneous SrFe 12 O 19 nanoparticles consisting of a single-domain structure at low sintering or calcination temperature, various methods have been introduced so that a wide grain size distribution with anomolous grain growth promoted during sintering could be avoided. The methods include co-precipitation [9, 10], salt-melt method [11], hydrothermal [12, 13], microemulsion [14], and sol–gel process [1, 4, 15]. Among these methods, sol–gel route is a low-cost, simple, and reliable method to control the stoichiometry and to produce nanocrystalline ferrite.…”

“…Besides, metal salts can be dissolved in many kinds of organic solvents, thus forming metal complexes by chelating the metal ions with organic ligands [17]. There are several sol–gel modification processes have been reported, such as pH adjustment [1, 18], basic agent [3], surfactant [1], carboxylic acid [2], and starting metal salts [3], to reduce the final calcination temperature, crystallite size [2], and high anisotropy of SrFe 12 O 19 nanoparticles [12]. In sol–gel methods, the ability to form hydroxides and/or oxides strongly depends on the pH of the solution and the charge/radius ratio of the metal cation [17].…”

Effect of Sonication Output Power on the Crystal Structure and Magnetism of SrFe12O19 Nanoparticles

“…The hexagonal ferrite type-M is denoted by the formula MFe 12 O 19 , where M is a divalent metal ion, typically Sr 2+ , Ba 2+ , or Pb 2+ [2]. Since its discovery in 1950 [3], the hexagonal ferrite type-M SrFe 12 O 19 has played an important role in hard magnetic materials and has been studied for decades due to its good chemical stability, ferrimagnetic behavior, high Curie temperature, high saturation magnetization, high coercivity, high magneto-crystalline anisotropy (MCA), and it is inexpensive compared to similar compounds [4][5][6]. As it has magnetization values of about 60 Am 2 /kg and coercivity of 4.37 × 10 5 A/m, it is widely used in magnetic recording material, data storage devices [7], magneto-optical recordings, microwave devices [8], permanent magnets, and electromagnetic devices [9].…”

“…As it has magnetization values of about 60 Am 2 /kg and coercivity of 4.37 × 10 5 A/m, it is widely used in magnetic recording material, data storage devices [7], magneto-optical recordings, microwave devices [8], permanent magnets, and electromagnetic devices [9]. A number of recent studies have considered SrFe 12 O 19 nanoparticles (NPs) in a composite as a promising candidate material for biomedical applications, primarily because of their biocompatibility, an example of which is the treatment for cancer known as magnetic hyperthermia, where heat generated by magnetic nanoparticles in a radio frequency magnetic field is used to destroy malignant cells [10].…”

Synthesis of M-type SrFe12O19 by mechanosynthesis assisted by spark plasma sintering

“…This process produces large particles and consumes extensive energy. Nanostructured hexaferrites can be produced by different methods such as sol-gel [6,7], hydrothermal [8], coprecipitation [9], spraydrying and microemulsion [10], conventional route [11] among others [12,13]. A particular method is mechanosynthesis; typically this method promotes formation of ferrites by mechanical activation of carbonate strontium and iron oxide [13,14].…”