Abstract
Magnetically hard-soft (100-x) SrFe12O19–x wt % La0.7Sr0.3MnO3 nanocomposites were synthesized via a one-pot auto-combustion technique using nitrate salts followed by heat treatment in air at 950 °C. X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM) were used to characterize the structural and magnetic properties of the samples. XRD spectra revealed the formation of a mixture of ferrite and magnetite phases without any trace of secondary phases in the composite. Microstructural images show the proximity grain growth of both phases. The room temperature hysteresis loops of the samples showed the presence of exchange-coupling between the hard and soft phases of the composite. Although saturation magnetization reduced by 41%, the squareness ratio and coercivity of the nanocomposite improved significantly up to 6.6% and 81.7%, respectively, at x = 40 wt % soft phase content in the nanocomposite. The enhancement in squareness ratio and coercivity could be attributed to the effective exchange-coupling interaction, while the reduction in saturation magnetization could be explained on the basis of atomic intermixing between phases in the system. Overall, these composite particles exhibited magnetically single-phase behavior. The adopted synthesis method is low cost and rapid and results in pure crystalline nanocomposite powder. This simple method is a promising way to tailor and enhance the magnetic properties of oxide-based hard-soft magnetic nanocomposites.
Highlights
Composites with magnetically hard and soft phases can improve magnetic properties because of the presence of high exchange-coupling of both phases
This study reports the preparation of hard-soft SrFe12 O19 (Ms~59.66 emu/g and high coercive field field (Hc)~3.6 kOe)-La0.7 Sr0.3 MnO3 (Ms~52.42 emu/g and Hc~0.052 kOe) exchange-coupled nanocomposites using the auto-combustion synthesis technique
It is understandable that the La0.7 Sr0.3 MnO3 (LSMO) and SrFe12 O19 (SFO) phases are compatible because these two phases can coexist without forming secondary phases
Summary
Composites with magnetically hard and soft phases can improve magnetic properties because of the presence of high exchange-coupling of both phases. Following the success of the observed phenomenon of exchange-coupling in the metallic hard-soft systems, efforts have been directed to studying the exchange-coupling phenomenon in oxide-based hard-soft composite magnets. Many studies on exchange-coupled hard-soft composites have been reported, where ferrites are used as a magnetically soft-phase, such as SrFe10 Al2 O19 /NiZnFe2 O4 [6], SrFe12 O19 /γ-Fe2 O3 [7], CoFe2 O4 /Fe3 O4 [8], BaFe12 O19 /Ni0.8 Zn0.2 Fe2 O4 [9], Fe3 O4 /BaCa2 Fe16 O27 [10], SrFe12 O19 /CoFe2 O4 [11], SrFe10 Al2 O19 /Co0.8 Ni0.2 Fe2 O4 [12], and SrFe12 O19 /La0.7 Sr0.3 MnO3 [13]. Is a unique combination of combustion and the chemical gelation processes This method exploits the advantages of cheap precursors, simple preparation, and atomic-level diffusion and results in ultrafine, homogeneous, crystalline powder [21,22,23,24]. The exchange-coupled nanocomposite was successfully prepared via an auto-combustion technique as they exhibit smooth hysteresis loops with high Mr/Ms and coercivity values
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