Terahertz-infrared dielectric properties of lead-aluminum double-cation substituted single-crystalline barium hexaferrite
Asmaa Ahmed, Anatoly S. Prokhorov, Vladimir Anzin, Denis Vinnik, Sergei Ivanov, Adam Stash, Y. S. Chen, Alexander Bush, Boris Gorshunov, Liudmila Alyabyeva
Hexaferrite materials are highly demanded to develop and manufacture electronic devices operating at radio- and microwave frequencies. In the light of the prospects for their use in the forthcoming terahertz electronics, here, we present our results on the terahertz and infrared dielectric response of a typical representative of hexaferrites family, lead-substituted M-type barium hexaferrite doped with aluminum, Ba0.2Pb0.8AlxFe12-xO19, x(Al)=0.0, 3.0, and 3.3. We studied uniquely large and high-quality single crystals of the. Systematic and detailed investigations of the dependences of terahertz-infrared (frequencies 8 - 8000 cm-1) spectra of complex dielectric permittivity on the temperature, 4 - 300 K, and on the chemical composition, x(Al)=0.0, 1.2, 3.0, 3.3, were performed for polarizations of the electric field E-vector of the probing radiation normal and parallel to the crystallographic c-axis. A number of resonance absorption bands are discovered at infrared-terahertz frequencies and assigned to polar phonons and transitions between energy levels of the fine-structured ground state of Fe2+ (5E) ions. In contrast to undoped BaFe12O19, no softening of the lowest frequency A2u phonon is observed, indicating suppression of a displacive phase transition in substituted compounds. Basing on dielectric data and detailed X-ray experiments, we find that for all concentrations of Al3+ ions, x(Al)=0.0, 1.2, 3.0, and 3.3, they mainly occupy the 2a and 12k octahedral site positions and that the degree of substitution of iron in tetrahedral positions is not substantial. Along with fundamental findings, the obtained data on broad-band dielectric properties of Ba0.2Pb0.8AlxFe12-xO19 crystals provides the information that can be used for development and manufacture of electronic devices with operating frequencies lying in the terahertz spectral band.
Thin hexagonal barium hexaferrite particles synthesized using the microemulsion technique were studied. A water-in-oil reverse microemulsion system with cetyltrimethylammonium bromide (CTAB) as a cationic surfactant, n-butanol as a co-surfactant, n-hexanol as a continuous oil phase, and an aqueous phase were used. The microstructural and magnetic properties were investigated. The particles obtained were mono-domain with average particle size 280 nm. The magnetic properties of the powder were investigated at 4.2 K and at room temperature. The saturation magnetization was 48.86 emu/g and the coe…
Vanadium substituted SrM hexaferrites (SrFe12-xVxO19 with x = 0.2, 0.4) and Eu-substituted BaM hexaferrite (Ba0.8Eu0.2Fe12O19) were prepared by high energy ball milling and sintering at 1200° C. X-ray diffraction measurements revealed that the V-substituted SrM samples exhibited phase separation resulting in the coexistence of the pure SrM magnetic phase with nonmagnetic Sr3(VO4)2 vanadate and α-Fe2O3 iron oxide phase. Also, the Eu-substituted BaM hexaferrite revealed the formation of the pure BaM phase coexisting with α-Fe2O3 secondary phase, and Eu-garnet minor phase. Although the magnetic p…
High density magnetic recording requires high coercivity magnetic media and small particle size. Barium hexaferrite has been considered as a leading candidate material because of its chemical stability, fairly large crystal anisotropy and suitable magnetic characteristics. In this work, we present the preparation of the hexagonal ferrite BaFe12O19 and one of its derivative; the Zn-Sn substituted hexaferrite by the chemical co-precipitation method. The main advantage of this method on the conventional glass-ceramic one, resides in providing a small enough particle size for magnetic recording. W…
The intrinsic ferroelectricity and related dielectric properties of M-type Barium Hexaferrite (BaFe12O19) with excellent magnetic performance are reported in this paper. A classic electric polarization (P-E) hysteresis loop with full saturation, together with two nonlinear reversal current peaks in the I-V curve and huge change of dielectric constant in the vicinity of Curie temperature, have all demonstrated themselves as sufficient experimental evidences to verify the ferroelectricity of BaFe12O19 ceramics. It holds a large remnant polarization at 108 uC/cm2 and a suitable coercive field at …
The site preference and magnetic properties of Zn, Sn and Zn-Sn substituted M-type strontium hexaferrite (SrFe$_{12}$O$_{19}$) have been investigated using first-principles total energy calculations based on density functional theory. The site occupancy of substituted atoms were estimated by calculating the substitution energies of different configurations. The distribution of different configurations during the annealing process at high temperature was determined using the formation probabilities of configurations to calculate magnetic properties of substituted strontium hexaferrite. We found…
Due to the limited rare-earth elements resources, ferrite magnets need to be improved drastically. Ideally, for a true hard magnet, the coercive field should be larger than the saturation magnetization, which is not yet realized for ferrites. Thus, an alternative can be found in making very fine grain ferrite magnets, but it is usually impossible to get small grains and dense material together. In this paper, it is shown that the spark plasma sintering method is able to produce approximately 80% of dense material with crystallites smaller than 100 nm. The as-prepared bulk sintered anisotropic …
We use first-principles total-energy calculations based on density functional theory to study the site occupancy and magnetic properties of Al-substituted $M$-type strontium hexaferrite SrFe$_{12-x}$Al$_{x}$O$_{19}$ with $x=0.5$ and $x=1.0$. We find that the non-magnetic Al$^{3+}$ ions preferentially replace Fe$^{3+}$ ions at two of the majority spin sites, $2a$ and $12k$, eliminating their positive contribution to the total magnetization causing the saturation magnetization $M_s$ to be reduced as Al concentration $x$ is increased. Our formation probability analysis further provides the explan…
In this article, common experimental techniques and preparation conditions adopted for the synthesis of M-type hexaferrites and their influence on the magnetic properties are briefly reviewed. The effects of various strategies of cationic substitutions on the properties of the hexaferrites are addressed. Further, our synthesis and findings on Co-Ti substituted hexaferrites are presented. It was found that Co-Ti substitution results in improving the saturation magnetization, and reducing the coercivity down to values favorable for high density magnetic recording. Also, evidence of inter-particl…
Simultaneous occurrence of big ferroelectricity and strong ferromagnetism has been observed in Barium Hexaferrite ceramics. Barium hexaferrite (BaFe12O19) powders with hexagonal crystal structure have been successfully synthesized by polymer precursor method using barium acetate and ferric acetylacetonate as the precursor. The powders were pressed into pellets, which were sintered into ceramics at 1100^{\circ}C~1300^{\circ}C for 1 hour. The structure and morphology have been determined by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Large spontaneous polariz…
We present a corroborative study of structural characterization of lithium substituted barium vanadate glasses using Raman and Electron Paramagnetic Resonance (EPR) spectroscopy. Investigation of the thermal and physical properties of these glasses showed a gradual increase in the concentration of non-bridging oxygen. Raman and EPR analysis gave an insight into the changing structure of the glasses. Both the spectroscopic techniques confirmed that vanadium is present in the glasses as distorted VO6 octahedra. From the analysis of both spectroscopic techniques, it is proposed that the lithium i…
The present study is concerned with the fabrication and characterization of Me2Y substituted hexaferrites, Ba2Me2Fe12-xTxO22 (Me = Co2+, Mg2+, and Cr2+, and T = Fe3+, and Ga3+). The samples were prepared by the conventional ball milling technique and sintering at 1200° C. The effect of the choices of Me and T ions on the structural and magnetic properties of the hexaferrites were investigated. XRD patterns, magnetic parameters, and Mössbauer spectra of the Co2Y were consistent with a single phase Y-type hexaferrite. However, the CoCr-Y sample was found to be dominated by the Y-type hexaferrite…
Ba{[Gax,Tax]Ti(1-2x)}O3 ceramics with x equal to 0, 0.0025, 0.005, 0.01, 0.025 and 0.05 have been prepared by conventional solid-state reaction. Structural and dielectric characterization have been performed to investigate the effect of dipole-pair substitution concentration on the macroscopic dielectric properties. Ba{[Gax,Tax]Ti(1-2x)}O3 evolves from a classic ferroelectric to a diffuse phase transition (DPT) as x increases. Ba{[Gax,Tax]Ti(1-2x)}O3 for x > or = 0.01 possesses diffuseness parameters comparable to Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) and recently reported (Ba0.97Pr0.03)(Ti0.9425Ce…
Temperature Dependent Magnetic and Structural Properties of Al Substituted Nanostructured Ferrites with Large Coercive Fields
University of Genoa（热那亚大学）；Uppsala University（乌普萨拉大学）；Lomonosov Moscow State University（莫斯科罗蒙诺索夫国立大学）；Le Mans Université（勒芒大学）；Nuclear Physics Institute of the CAS（捷克科学院核物理研究所）；CNR-SPIN（国家研究中心自旋物理研究所）；Università Ca’ Foscari Venezia（威尼斯卡福斯卡里大学）
The effects of non-stoichiometric lattice structure and secondary phase α-Fe2O3 on modifying the magnetic, electrical, and magneto-electric properties of Eu doped BaFe12O19 hexaferrite
Pondicherry University（本地治里大学）；UGC – DAE Consortium for Scientific Research Mumbai Centre, Bhabha Atomic Research Centre（UGC-DAE科学研究联合体孟买中心，巴哈原子研究中心）
