Magnetic and optical properties of Gd-Tl substituted M-type barium hexaferrites synthesized by co-precipitation technique

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Highlights

  • The synthesis performed via co-precipitation process with Gd-Tl substitution.

  • A magneto-plumbite structure was achieved.

  • Gd-Tl substitution influenced the band gap (2.47–1.74 eV) with decreasing trend.

  • The platelet-like shape with size 0.415–0.446 μm of hexaferrites was observed.

  • The sample x = 0.25 presented excellent magnetic characteristic such as Ms = 51.727 emu/g, Hc = 4.057 kOe and Mr = 28.061 emu/g.

Abstract

The substitution of numerous cations into hexagonal ferrite has been extensively used to endow novel properties and functionalities for various applications. In the present work Gd-Tl substituted barium hexaferrites prepared by co-precipitation process, having the composition Ba0.75Cu0.25(GdxTl0.5-x)Fe11.5O19 (x = 0.0, 0.25 and 0.50). The hexaferrite formation during calcination of sample x = 0.25 was confirmed by TGA/DSC which was processed at 1000 °C for 3 h. The analysis of X-ray diffraction depicts the existence of magneto-plumbite structure with the formation of a minor secondary α–Fe2O3 phase x ≤ 0.0 and BaFe2O4 phase x ≤ 0.50. UV–Vis spectra reveal the dropping down behavior in the optical energy band gap from 2.47 eV to 1.74 eV. The grains with hexagonal platelet-like shape having size of 0.415–0.446 μm of magnetic powder nanoparticles (MPs) are observed by SEM images. The energy dispersive spectrometer (EDS) analysis was employed for presence of ferrite elements within a single particle. Hysteresis loops signifies the magnetization (Ms) and remnant magnetization (Mr) first increases up to x = 0.25 then reduces with the substitution (x) increment; contrarily, the coercivity (Hc) exhibited initially decreased with maximum content of Tl at x = 0.0 then increases at x = 0.25 after that it decreases at x = 0.50. Maximum values such as Ms (51.727 emu/g), Mr (28.061 emu/g), and Hc (4.057 kOe) are attained for x = 0.25 at room temperature. The synthesized magnetic nanoparticles are found to be suitable for microwave absorbing materials, permanent magnets, catalyst, high density recording media and optoelectronic devices.

Introduction

The well-established magnetoplumbite barium hexaferrite (BaM) ceramic has achieved much attention due to the revolution in numerous technological applications. The revolution in 21st century in hexagonal ferrites has strongly increased which is directly associated with the discovery of unique magnetic materials. These are applicable in many areas, such as communication, electronics, low-loss microwave, organic electronics, permanent magnets, ferroelectric photovoltaics devices, microwave devices, magnetic fluids and magnetic algal separation materials in view of their excellent magnetic characteristics and low cost [[1], [2], [3], [4], [5]], etc. The high coercive field is the most interesting property of these existing hexaferrites. According to the technological perspective, the permanent magnets should have the high coercive field while the soft magnet have low coercive field for a magnetic recording applications [3]. The hexagonal unit cell of BaM was composed of ten layers of oxygen. The five interstitial sites in between these layers are occupied by Fe+3 ions; these five sites are named as one bipyramidal (2b), one tetrahedral (4f1) and octahedral (12k, 2a and 4f2). The upward spin direction possessed by (12k, 2a and 4f2) sites and the downward spin directions by 4f2 and 4f1 sites [7,8].

Until now the hexaferrites have been synthesized by several techniques, such as solid state reaction [6], sol-gel auto-combustion [7], hydrothermal [8], standard ceramic [9], co-precipitation [3] and various wet methods have been employed for the attainment of tunable magnetic properties. The adoption of co-precipitation technique for hexaferrites has a leading edge, like low cost, facile operation, less time for reaction, normal temperature and homogeneity in particles with narrow size [3]. For the applications point of view, tuning the coercive field is crucial in hexaferrites. The high magnetocrystalline anisotropy strongly depends on the high coercivity, which arises due to the well-built exchange coupling in-between the spins of Fe+3 at different sites of hexaferrites [10]. The magnetic or non-magnetic cations substitution by Fe+3 ions in hexaferrites create an effective influence on the magnetocrystalline anisotropy. The magnetic behavior such as remnant magnetization (Mr), coercivity (Hc) and saturation magnetization (Ms) could be optimized by cations substitution of trivalent or divalent ions. In general, magnetic, optical structural and mechanical properties of BaM are directly associated with site occupancy of each ion on the five interstitial positions of Fe+3 ions by a trivalent metal ions.

Several metal cations substitution in BaM has been published significantly. For example, Hojjati et al. [11] reported Al substitution in BaM to investigate Al+3 ions impact on magnetic values. The enhancement was observed in coercivity up to x = 1.5 then decreased while Ms exposed decline trend. Trukhanov et al. [6] prepared Ga+3 doped barium hexaferrites and reported the variations in magnetic parameters with decreasing behavior of Ga+3 concentration. Ihsan et al. [12] substituted Cr-Ga in BaM via sol-gel technique and described the enrichment in magnetic parameters with the influence of Cr-Ga contents. Turchenko et al. [13] studied the outcome of In+3 and Ga+3 replacement on dual ferroic properties of BaM. Tsuzuki et al. [14] prepared Al+3, Ga+3 and In+3 substituted in BaM by glass-ceramic route and depicted the decline behavior of magnetic properties. Litsardakis et al. [15], explored Gd-Co substitution in BaM and observed that Hc increased up to x = 0.2, then decreased, while Ms and Mr decreased with respect to substitution. Majid et al. [3] substituted Gd-Nd in barium hexaferrite via co-precipitation technique. It revealed that falling down trend of Ms and Hc was achieved. Ishtiaq et al. [16] used co-precipitation route to prepare Gd substitution in Ba-Co based M-type hexaferrites and obtained the lower values of Hc and higher values of Ms. Nazia et al. [17] explored the influence of Gd-Zn substitution on structural and dielectric behavior of Ca-Ba based M-type hexaferrites. Yujie et al. [18] used Gd–Co substitution into M-type hexaferrites system via standard ceramic technique. The reported Ms and Mr values were reduced from 0.00 to 0.32 of Gd-Co content (x) while Hc values first increased from 0.00 to 0.24 and then decreased (x) ≥ 0.24. To date, the above mentioned researches have been accomplished to explore the influence of different substituents on magnetic behavior and structure of BaM to make them robust. Although a tremendous work has been reported on BaM ferrites, the simultaneous investigation of the variation in magnetic properties of BaM with Tl+3 and Gd+3 ions substitution has not been reported earlier.

This investigation reveals the influence of the substitution of trivalent Tl+3 and Gd+3 cations on the structural, optical, morphological and magnetic behavior of Ba-Cu based M-type hexaferrites. In this view, novel BaM nanocomposites having composition Ba0.75Cu0.25(GdxTl0.5-x)Fe11.5O19 (x = 0.0, 0.25 and 0.50) have been synthesized by a co-precipitation technique.

Section snippets

Materials

The reagents utilized during co-precipitation for the formation of Gd-Tl substituted Ba-Cu based M-type hexaferrites were of analytical grade. Barium nitrate dehydrate (Ba(NO3)2.2H2O), iron (III) chloride (FeCl3.6H2O), CuCl2.2H2O (99%, Merck), Gd2O3 (99%, Aldrich), Tl(NO3)3 and NaOH (33%, Aldrich) were served as the initial chemicals. The deionized water was used to prepare solutions.

Synthesis of hexaferrites

Ba-Cu M-type hexaferrites with nominal composition Ba0.75Cu0.25(GdxTl0.5-x)Fe11.5O19 (x = 0.0, 0.25, 0.50) were

TGA/DSC analysis

To explore the formation of hexagonal phase for substituted Ba-Cu based hexaferrite powder, the TGA/DSC analysis was used to determine the decomposition phenomena. Fig. 1 shows the TGA/DSC curves within the temperature regime of 25–1200 °C for the dried precursor with nominal composition Ba0.75Cu0.25(Gd0.25Tl0.25)Fe11.5O19 (x = 0.25) in air atmosphere. Accordingly, the increment in temperature resulting in the weight loss was observed in different stages in the TGA curve. As it can be seen in

Conclusions

Ba-Cu based M-type hexaferrites with Gd-Tl substitution have been prepared by co-precipitation method. Gd-Tl substituted barium hexaferrite with general formulae Ba0.75Cu0.25(GdxTl0.5-x)Fe11.5O19 (x = 0.0, 0.25, 0.50), have been found stable at with calcination temperatures of 1000 °C for about 3 hours, as verified by TGA/DSC analysis. The development of pure hexagonal ferrite phase has been confirmed by XRD and FTIR studies. XRD analysis present that M-type as major phase for all MPs while the

Acknowledgements

This work was supported in part by the Science and Technology Commission of Shanghai Municipality (Grant Nos. 15DZ2260303 and 16DZ2260602) and National Key Research and Development Program of China (Grant No. 2017YFB0701900).

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