Study of the Structural and Magnetic Properties of Co-Substituted Ba2Mg2Fe12O22 Hexaferrites Synthesized by Sonochemical Co-Precipitation

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.

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

“…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.…”

Phase Transitions in Magneto-Electric Hexaferrites

“…ZFC and FC magnetization as a function of the temperature for Ba 2 Mg 0.4 Co 1.6 Fe 12 O 22 in a magnetic field of (a) 50 Oe, (b) 100 Oe, (c) 500 Oe, and (d) 1 kOe. Reprinted with permission from ref . Copyright 2019 MDPI.…”

“…Rhee et al 27 investigated the ZFC magnetization changes for Ba 2 Co 2 Fe 12 O 22 in a magnetic field of 100 Oe; they observed the magnetic phase transition from a helimagnetic spin ordering to a ferromagnetic one to take place at 215 K and determined the T N to be 615 K. The Neél temperature is higher than that for Ba 2 Mg 2 Fe 12 O 22 and Ba 2 Zn 2 Fe 12 O 22 due to the presence of the magnetic Co 2+ cation leading to stronger superexchange interactions Co 2+ − O 2− −Fe 3+ (Co 2+ ). Lim et al 53 studied the ZFC magnetization of Ba 2 Mg 0.5 Co 1.5 Fe 12 O 22 in the 50−740 K temperature interval and a magnetic field of 100 Oe and detected a magnetic phase transition from a helimagnetic spin ordering to a ferromagnetic one at 206 K. Our studies 42 on the influence of the partial substitution of nonmagnetic Mg 2+ cations with magnetic Co 2+ cations in Ba 2 Mg 0.4 Co 1.6 Fe 12 O 22 showed that the phase transition temperature is rather sensitive to the applied magnetic field strength, namely, it decreases from 225 K (at 50 Oe) to 135 K (at 1 kOe). We also observed a different behavior of the ZFC curves for magnetic field strengths exceeding 500 Oe.…”

“…Lim et al . studied the ZFC magnetization of Ba 2 Mg 0.5 Co 1.5 Fe 12 O 22 in the 50–740 K temperature interval and a magnetic field of 100 Oe and detected a magnetic phase transition from a helimagnetic spin ordering to a ferromagnetic one at 206 K. Our studies on the influence of the partial substitution of nonmagnetic Mg 2+ cations with magnetic Co 2+ cations in Ba 2 Mg 0.4 Co 1.6 Fe 12 O 22 showed that the phase transition temperature is rather sensitive to the applied magnetic field strength, namely, it decreases from 225 K (at 50 Oe) to 135 K (at 1 kOe). We also observed a different behavior of the ZFC curves for magnetic field strengths exceeding 500 Oe.…”

Real-Time Observation of Magnetic Domain Structure Changes with Increasing Temperature for Z-Type Hexagonal Ferrite

“…Using various divalent cations (Ba, Sr, and Co) and tuning the stoichiometry, hexagonal ferrites of several sorts (M, Y, Z, W, X, and U) can be produced [ 1 , 7 ]. Magnetoelectric (ME)/multiferroic phenomena are one of the most exciting discoveries of hexagonal ferrites [ 7 , 8 , 9 ]. Previous studies have revealed that magnetically induced ferroelectricity can be manifested by complex internal arrangements of magnetic moments in hexagonal ferrites, in which ferromagnetic properties are intrinsically coupled to their atomic structures [ 1 , 7 , 8 , 10 , 11 , 12 , 13 , 14 ].…”