Micro/nanosized ferrite and hexaferrite structures: The polyol processes for synthesis

In this research, controlled synthesis and properties of micro/nano-sized magnetic oxide powders via a polyol process are discussed. They are the original magnetic oxides that have been studied by many scholars because of their many applications. The most special forms are the diversity of FeO and Fe 2 O 3 , and the diversity of the Fe 3 O 4 matrix which are the most important original structures with formulas to be FeO.Fe 2 O 3 (Fe 3 O 4 ) and Fe 2 O 3 can be oxide systems of Fe x O y that are very common and different. On the basis of the original structures, we can synthesize the most special forms of ferrite and hexaferrite related to the four original structures, which are AB 2 O 4 - spinel-type SrFe 2 O 4 and BaFe 2 O 4 ferrites (M: metal elements, Sr, Ba; B: Fe), PbFe 11 AlO 19 -type MX 12 O 19 (M: metal elements, Sr, Ba; X: Fe) SrFe 12 O 19 and BaFe 12 O 19 by polyol processes and technologies. We understand that elements that form original structures are incorporated into Fe 3 O 4 to form ferrite and hexaferrite structures, typically such as SrFe 12 O 19 by liquid, solid-and gas-based phase chemical reactions via the polyol processes and heat treatment processes. In the future, we suggest that the original oxide structure and formula of natural minerals can be used as the new magnetic structures and compounds.

Citation: Long  are the so-called mixed magnetic oxides and ceramics.The unlimited potential applications of the various kinds of ferrites and hexaferrites are clearly confi rmed in electronics and telecommunications [1,2].Additionally, magnetic alloys can be formed by the technologies of sintering or heat treatment with the change of magnetic oxides into magnetic alloys with reducing agents at high temperatures (CaH 2 , H 2 , solid and common gas-reducing agents by sintering processes) [4].
Therefore, original magnetic properties need to be enhanced, changed, and retained in the structural modifi cations of the above various structures.In this research, we understand that the new, modifi ed, and easy-to-apply polyol processes, and heat treatment processes are effectively used for the controlled synthesis of the above original structures that are crucial to researchers.As a result, we present a typical experimental preparation of SrFe 12 O 19 hexaferrite in our investigations and experiences.

Processes
In a typical process, the magnetic oxide powders based on the so-called original structures were carefully prepared with a reducing agent, and heat treatment after chemical synthesis under control [4,5]

Results and discussions
In recent studies, we found out that Fe In this study, we aim to focus on the future perspectives of mixed ferrites and hexaferrites from the defi ned original crystal structures, typically such as oxide systems of FeO,  synthesis approach according to their potential applications for electronics and telecommunications, especially such as the various kinds of new ferrite and hexaferrite magnets.

NH 4
OH, and kinds of H 2 O, respectively.Sr-Fe-O oxide powder products after cleaning polymer were obtained and dried into micro/nanosized magnetic powders at 200-240 °C.The powder samples of ferrite and hexaferrite were heated at 950 °C in a furnace to obtain the fi nal powder with a metallic bright-black color.The as-prepared powders were measured by a vibrating sample magnetometer (VSM), Model10-VSM, MicroSense, and demagnetization fi eld in the range of -1500 to +1500 Oe.The structures of Sr-Fe-O and SrFe 12 O 19 samples were investigated by X-ray diffraction (XRD) (D2 Phaser/Bruker AXS diffractometer, Germany).
3 O 4 -type oxide exhibited original structures for the potential of producing other new structures due to their very porous structures of noncrystals or crystals that are very good for the integration of ion metal others or ion rare earth elements into the common porous matrix.It means that micro/nanosized ferrite and hexaferrite can be produced in a variety of porous Fe 3 O 4 -type matrices.We also found that there was a coexistence of the two crystalline phases of -Fe 2 O 3 (minor phase) and SrFe 12 O 19 (major phase).The as-prepared structure of SrFe 12 O 19 was assigned to the standard pattern to be PDF#33-1340 (Strontium iron oxide; CuKa1; Hexagonal; P63/mmc(194); Eight strong lines; Strongest line: (114)).However, the XRD data and results were not presented here.It is evidenced that the most typical magnetic parameters of micro/nanosized SrFe 12 O 19 oxides are calculated to be Ms about 33.35 (emu/g), Mr (remanent magnetization: M at H = 0) to be 18.64 (emu/g), and Hc (coercive fi eld: Field at which M/H changes sign) to be 5072.22(Oe) in the average values, respectively (Figure 1).The high value of BH max = 2313 MGOe (Maximum energy loss of the hysteresis loop) is measured.We show that superparamagnetism was transformed into ferrimagnetism when the Sr element was incorporated into the porous original structure of Fe 3 O 4 to form the original crystal structure of SrFe 12 O 19 at high temperatures.

Fe 3 O 4 ,
Fe 2 O 3 , SrFe 12 O 19 , and BaFe 12 O 19 by the polyol processes and technologies with heat treatment on industrial synthesis approach.At present, no evidence is available for the formation of hexaferrites through the chemical reaction in common solutions and solvents (i.e., H 2 O, ethanol, methanol, and various industrial glycols) as that will be the new research trend for synthesis [6].The authors, N.V.Long and N.T.N.Hang have used the original equation of controlled synthesis of porous Fe 3 O 4 crystal oxides (the Elmore reaction [7], an important and meaningful reaction, i.e.FeCl 2 + 2FeCl 3 + 8NaOH → Fe 3 O 4 + 8NaCl + 4H 2 O for small scale synthesis in the laboratory, and the ideas of industrial synthesis approach at large scale; NaOH, KOH, and NH 4 OH are also important in experimental; NaBH 4 , KBH 4 , and other agents are suitable catalysts for the formation according to time and reaction temperature) as a discovery of black box equation for the synthesis of nano/microsized ferrites and hexaferrites that are formed in heat treatment.The original systems of nano/microsized ferrites and hexaferrites are formed by heat treatment.It means that the mixed oxides such as Mn-Fe-O, Co-Fe-O, Ni-Fe-O, Mg-Fe-O, Zn-Fe-O, and others based on the original Fe 3 O 4 -type forms are effectively formed in the highest crystallization of MFe 2 O 4 (M: Mn 2+ , Co 2+ , Ni 2+ , Mg 2+ , Zn 2+ etc) by sintering or heat processes [3-8].To improve the ferrimagnetism of MFe 2 O 4 , the Co element is added in the experiments to form the modifi ed and mixed oxide structures with the formula of M x X y Fe 2 O 4 (M: Mn 2+ , Ni 2+ , Mg 2+ , Zn 2+ and others; X: Co 2+ ; x + y = 1; x = y = 0.5).Rare earth can be incorporated into Fe 3 O 4 -type matrix for the formation of RFeO 3 and ABO 3 (original structure of perovskite; R: Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; typically as HoFeO 3 ; A: Bi; B: Fe; typically as CaTiO 3 -type BiFeO 3 ).Thus, the same polyol process for the synthesis of hexaferrite with the original formula of MFe 12 O 19 (M: Ba, Sr; BaFe 12 O 19 ; SrFe 12 O 19 ; Sr x Ba y Fe 12 O 19 ; x + y = 1; x = y = 0.5) in our research open a new way of controlled synthesis for the new kinds of mixed ferrites and hexaferrites, by industrial
Based on their crystal structures, original ferrite and hexaferrite structures are meaningful for the further investigation of new, modifi ed, and mixed ferrites and hexaferrites.The polyol process can lead to polyol technology (N.V. Long and N.T.N.Hang's new ideas of "original equation for synthesis", and "original structures and formulas of materials for research") for the controlled synthesis of new magnetic mixed nanomaterials in the future.In this study, the Fe 3 O 4 matrix (a special form of ferrite) is very important in order to synthesize the structure of MFe 2 O 4 (M: metal; micro/ nanosized ferrites; Fe: major element), and MFe 12 O 19 (M: Sr, Ba; micro/nanosized hexaferrites; Fe: major element).