Abstract
Ba2Mg0.4Co1.6Fe12O22 was prepared in powder form by sonochemical co-precipitation and examined by X-ray diffraction, Mössbauer spectroscopy and magnetization measurements. Careful XRD data analyses revealed the Y-type hexaferrite structure as an almost pure phase with a very small amount of CoFe2O4 as an impurity phase (about 1.4%). No substantial changes were observed in the unit cell parameters of Ba2Mg0.4Co1.6Fe12O22 in comparison with the unsubstituted compound. The Mössbauer parameters for Ba2Mg0.4Co1.6Fe12O22 were close to those previously found (within the limits of uncertainty) for undoped Ba2Mg2Fe12O22. Isomer shifts (0.27–0.38 mm/s) typical for high-spin Fe3+ in various environments were evaluated and no ferrous Fe2+ form was observed. However, despite the indicated lack of changes in the iron oxidation state, the cationic substitution resulted in a significant increase in the magnetization and in a modification of the thermomagnetic curves. The magnetization values at 50 kOe were 34.5 emu/g at 4.2 K and 30.5 emu/g at 300 K. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves were measured in magnetic fields of 50 Oe, 100 Oe, 500 Oe and 1000 Oe, and revealed the presence of two magnetic phase transitions. Both transitions are shifted to higher temperatures compared to the undoped compound, while the ferrimagnetic arrangement at room temperature is transformed to a helical spin order at about 195 K, which is considered to be a prerequisite for the material to exhibit multiferroic properties.
Highlights
Multiferroic materials form a special category of magnetic materials characterized by the coexistence of long-range magnetic and ferroelectric orders, a property that has provoked keen interest from both fundamental and applied points of view [1,2,3,4]
In our previous studies [25,26], we showed that in a Ba2 Mg2 Fe12 O22 powder material synthesized by sonochemical co-precipitation, the magnetic phase transition from ferromagnetic-to-spiral spin order occurs at 196 K at a magnetic field of 100 Oe
The preliminary analysis of the diffraction pattern of the Ba2 Mg0.4 Co1.6 Fe12 O22 showed that, The preliminary analysis of the diffraction pattern of the Ba2Mg0.4Co1.6Fe12O22 showed that, besides the peaks corresponding to the Y-type hexaferrite phase, traces of a second phase with a besides the peaks corresponding to the Y-type hexaferrite phase, traces of a second phase with a spinel type structure were present
Summary
Multiferroic materials form a special category of magnetic materials characterized by the coexistence of long-range magnetic and ferroelectric orders, a property that has provoked keen interest from both fundamental and applied points of view [1,2,3,4]. One of the first magnetoelectric hexaferrites discovered was Ba2 Mg2 Fe12 O22 It possesses a somewhat relatively high spiral-magnetic transition temperature (~200 K), exhibits multiferroic properties at zero magnetic field, while one can manipulate the direction of the electric polarization using relatively weak magnetic fields (
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