Structure and Magnetic Properties of SrFe12O19/CoFe2O4 Nanocomposite Ferrite

Abstract

Nanocomposite particles SrFe12O19/ CoFe2O4 were synthesized by sol-gel method. The nanocomposites are formed at the calcining temperature around 850 oC in 5 hours. The phase composition, surface morphology and magnetic properties of the nanocomposites were investigated using XRD, SEM and VSM, respectively. The results show that the magnetic properties of nanocomposite particles are strongly influenced by the molar ratios of the hard and soft phases and particle size distributions. The samples with the mass ratio of Rm= SrFe12O19/ NiFe2O4 = 1/3 and 1/5 are characterized with a “bee waist” type hysteresis loop. While all the samples RV show an excellent smooth hysteresis loop and a single – phase magnetization behavior. The coercivity decreases significantly and the magnetization drastically increases with decreasing of volume ratio RV.
 Keywords: nanocomposite, sol- gel method, exchange coupling. 

Optimizing the magnetic properties of hard and soft materials for producing exchange spring permanent magnets

“…The stability of the SFO and spinel ferrite mixture upon calcination has been previously reported in the literature. [19,21,23] However, in these cases a calcination treatment was needed to fully crystallize the starting nanopowders. In our case, since the selected ZFO contains Fe 2+ , the calcination under oxygen will lead to the oxidation of the ferrite and to the formation of crystallographic phases with lower MS, such as maghemite or hematite.…”

“…Nevertheless, to the best of our knowledge, no cubic ferrites with MS larger than 95 Am 2 kg -1 have been explored to this purpose, to date. [15,20,22,23,26,27] An interesting example of combination of SFO with a metal oxide was reported by Jenus et al [26] The authors showed that the application of the spark plasma sintering technique to a mixture of SFO and cobalt ferrite magnetic nanoparticles (MNPs) prepared by hydrothermal synthesis, led to an increase of BHmax of ca. 20 %, up to 26.1 kJm -3 with respect pure SFO.…”

“…Large efforts have been spent in increasing the BHmax of SFO by combination with hard or soft spinel cubic ferrite (MFe2O4 M=Co, Fe, Mn) or metal alloys (FeCo). [19][20][21][22][23][24][25] In view of the possible production at the industrial scale, the use of metal oxides is particularly promising due to their stability against corrosion and mechanical processing. In principle, the fundamental requisite of a large enough magnetization to enhance the remanence of the composite is satisfied by several spinel ferrite, such as magnetite, nickel-zinc doped magnetite or zinc ferrite.…”

“…Among the hard materials investigated so far, strontium hexaferrite (SFO) has received large attention owing to its chemical stability, large availability, low production cost and good magnetic properties (saturation magnetization M S = 70-72 Am 2 kg −1 , coercivity H C = 400 kA m −1 and BH max close to 40 kJ m −3 ), characteristics that make it a leading candidate in the PM market. Large efforts have been spent on increasing the BH max of SFO by combination with hard or soft spinel cubic ferrite (MFe 2 O 4 M=Co, Fe, Mn) or metal alloys (FeCo) [19][20][21][22][23][24][25]. In view of the possible production at the industrial scale, the use of metal oxides is particularly promising due to their stability against corrosion and mechanical processing.…”

“…In principle, the fundamental requisite of a large enough magnetization to enhance the remanence of the composite is satisfied by several spinel ferrites, such as magnetite, nickel-zinc-doped magnetite or zinc ferrite. Nevertheless, to the best of our knowledge, no cubic ferrites with M S larger than 95 Am 2 kg −1 have been explored for this purpose to date [15,20,22,23,26,27]. An interesting example of combination of SFO with a metal oxide was reported by Jenus et al [26].…”