Study of Y-type hexaferrite Ba0.5Sr1.5ZnNiFe12O22 powders

Abstract

We report results from a study on the influence of the substitution of Zn 2+ cations in the Y-type Ba0.5Sr1.5Zn2Fe12O22 hexaferrite, known for strong magnetoelectric coupling, with magnetic cations, such as Ni 2+ , on its structural and magnetic properties. Polycrystalline samples of Ba0.5Sr1.5ZnNiFe12O22 were synthesized by citric acid solgel auto-combustion. The saturation magnetization value of 54.7 emu/g at 4.2 K was reduced to 37.2 emu/g at 300 K. The temperature dependence of the magnetization at magnetic fields of 50 Oe, 100 Oe and 500 Oe were used to determine the magnetic phase transition temperature. We demonstrate that the helical spin state, believed to cause the magnetoelectric effect, can be achieved by varying the magnetic field strength within a given temperature range.

Effect of cation substitutions in Y-type Ba0.5Sr1.5Me2Fe12O22 hexaferrites on the magnetic phase transitions

“…Another maximum at 40 K is also seen -it arises from the magnetic phase transformation from a spiral magnetic order to a conical spin order at low temperatures. Such a maximum was not observed in our earlier study on the Ba0.5Sr1.5ZnNiFe12O22 powder [9]; this indicates that replacing the Zn 2+ ionic species with the smaller Mg 2+ cations [19] leads to important changes in the paths of magnetic interactions leading to a conical spin structure arising at low temperatures. The ZFC and FC curves showing a stable magnetisation growth at temperatures approaching 300 K means that the temperature of transformation to a paramagnetic state exceeds this temperature, so that this transition could not be registered in the experiments reported here.…”

“…The synthesis of Y-type hexaferrites is commonly accompanied by the formation of different oxides, usually spinels, mainly because the temperature range for synthesising the Y-phase is rather narrow. However, in what concerns the magnetic phase transitions, our previous studies [9,12,13] on other Y-hexaferrite compositions have shown that the trace amount of spinel ferrites in the material studied does not affect the magnetic-phase transition temperatures. In figure 2, we display the initial magnetisation and the hysteresis curves of the Ba0.5Sr1.5NiMgFe12O22 powder at 300 K and 4.2 K. As seen, the magnetisation curves for both temperatures do not reach saturation at the highest magnetic field used of 50 kOe, the highest magnetisation values being 32 emu/g and 24 emu/g respectively at 4.2 K and 300 K. The magnetisation values determined are typical for Y-type hexaferrites.…”

“…The studies on the magnetic properties and magnetoelectric effect have been mainly focused on the Ba0.5Sr1.5Zn2Fe12O22 hexaferrite and on the effect of substituting Zn with other cations. The results of our previous works [8,9] on replacing the non-magnetic Zn 2+ with the magnetic Ni 2+ cations in Ba0.5Sr1.5Zn2-xNixFe12O22 demonstrated that a half substitution of Zn 2+ with Ni 2+ displaces the helical spin magnetic order to higher temperatures. Also, the electrical polarisation caused by a weak magnetic field in Ba2Mg2Fe12O22 has to do with the Mg 2+ cations reducing the magnetic anisotropy [10].…”

Phase Transitions in Magneto-Electric Hexaferrites

“…The average thickness of the Ba 2 Mg 2 Fe 12 O 22 particles was 380 nm. A similar microstructure was observed for Ba 0.5 Sr 1.5 Zn 2 Fe 12 O 22 . , …”

“…The precursors produced by these co-precipitation methods are synthesized at 1170 °C. We described in detail such a procedure for the synthesis of different Y-type hexaferrites. − We also reported , a comparative investigation on this synthesis method’s effect on the microstructural and magnetic parameters of Ba 2 Mg 2 Fe 12 O 22 powder materials and found that the ultrasonically assisted co-precipitation produced particles with a practically perfect hexagonal shape compared with the particles obtained by sol–gel autocombustion (Figure b). The average thickness of the Ba 2 Mg 2 Fe 12 O 22 particles was 380 nm.…”