Ibrahim Bsoul

Magnetic study of M-type doped barium hexaferrite nanocrystalline particles

Co-Ti and Ru-Ti substituted barium ferrite nanocrystalline particles BaFe12−2xCoxTixO19 with (0≤x≤1) and BaFe12−2xRuxTixO19 with (0≤x≤0.6) were prepared by ball milling method, and their magnetic properties and their temperature dependencies were studied. The zero-field-cooled (ZFC) and field-cooled (FC) processes were recorded at low magnetic fields and the ZFC curves displayed a broad peak at a temperature TM. In all samples under investigation, a clear irreversibility between the ZFC and FC curves was observed below room temperature, and this irreversibility disappeared above room temperature. These results were discussed within the framework of random particle assembly model and associated with the magnetic domain wall motion. The resistivity data showed some kind of a transition from insulator to perfect insulator around TM. At 2 K, the saturation magnetization slightly decreased and the coercivity dropped dramatically with increasing the Co-Ti concentration x. With Ru-Ti substitution, the saturation...

Effects of Heat Treatment on the Phase Evolution, Structural, and Magnetic Properties of Mo-Zn Doped M-Type Hexaferrites

In this article we report on the structural and magnetic properties of BaFe12-4xMoxZn3xO19 hexaferrites with Mo-Zn substitution for Fe ions. The starting materials were commensurate with the BaM stoichiometry, and the Mo:Zn ratio was 1:3. The powder precursors were prepared by high energy ball milling, and subsequently sintered at temperatures from 1100 to 1300° C. The structural analyses indicated that all samples sintered at 1100° C were dominated by a major M-type hexaferrite phase. The relative abundance of the BaMoO4 and Zn-spinel secondary phases increased with increasing the concentration of the substituents, resulting in a decrease of the saturation magnetization from about 67 emu/g (for x = 0.0) to 55 emu/g (for x = 0.3). The coercivity also decreased from 3275 Oe (for x = 0.0) to 900 Oe (for x = 0.3), demonstrating the ability to tune the coercivity to the range useful for magnetic recording by the substitution process. The saturation magnetization improved significantly with sintering at T > 1100° C, and the coercivity decreased significantly, signaling the transformation of the samples to soft magnetic materials. These magnetic changes were due to the high-temperature reaction of the spinel phase with the BaM phase to produce the W-type hexaferrite phase on the one hand, and to the growth of the particles on the other hand. The magnetic phases were further investigated using Mössbauer spectroscopy and thermomagnetic measurements. Our study indicated that the sample with x = 0.2 has the highest saturation magnetization (74 emu/g at sintering temperature of 1300° C) and a tunable coercivity between 2100 Oe and 450 Oe.

Effects of molybdenum concentration and valence state on the structural and magnetic properties of BaFe 11.6 Mo x Zn 0.4− x O 19 hexaferrites

Barium hexaferrites BaFe11.6MoxZn0.4−xO19 (x= 0.1, 0.2, 0.4) were prepared by precipitation of the precursors using wet chemical mixture method and then sintering the dried powders at 1100 °C. The properties of the prepared samples were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer, and Mössbauer spectroscopy. XRD patterns revealed that all prepared samples had BaFe12O19 hexaferrite structure as a majority phase. SEM images demonstated that the samples consisted mainly of hexagonal platelet-like grains with diameters ranging from 100 to 500 nm. Mössbauer spectra revealed that Zn2+ ions occupy 4f1 sites leading to the splitting of the 12k component. However Mo6+ ions occupy 2b sites while Mo4+ prefer 4f1 and 12k sites. For the sample with x = 0.4,Mo6+ and Mo4+ ions were found to have preference for 2b and 12k sites, respectively, and to induce the development of Fe2+ ions in the hexaferrite, leading to noticeable changes in the magnetic properties of the system. The observed magnetic properties were found to be consistent with the preferential site occupation of metal ions, and the hyperfine fields derived from Mössbauer spectra of these samples.

Modification of the Magnetic Properties of Co2Y Hexaferrites by Divalent and Trivalent Metal Substitutions

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, and M-type and BaCrO4 minority phases were observed in the XRD pattern of the sample. The small increase in saturation magnetization from about 34 emu/g up to 37.5 emu/g was therefore attributed to the development of the M-type phase. On the other hand, XRD pattern of the Cr2Y sample indicated the dominance of the M-type phase in this sample. The high coercivity (1445 Oe) of this sample is evidence of the transformation of the material from a typically soft magnetic material (Y-type) to a hard magnet (M-type). The Ga-substitution for Fe in Co2Y did not affect the saturation magnetization significantly, but the coercivity was reduced. However, the sample Ba2CoMgFe11GaO22 exhibited a significant reduction of the saturation magnetization down to a value 26.6 emu/g, which could be due to the attenuation of the super-exchange interactions induced by the Mg2+ substitution.

Structural and magnetic properties of Cu-V substituted M-type barium hexaferrites

In search of magnetic materials with improved magnetic characteristics for practical applications, M-type barium hexaferrites with Fe3+ ions partially substituted by a mixture of Cu and V ions were prepared by ball milling and sintering at 1200° C. The structural analyses of the prepared BaFe12-2xCuxVxO19 samples (x = 0.1, 0.2, 0.3, 0.4) revealed the presence of BaM phase, in addition to α-Fe2O3, Ba3V2O8, and BaFe2O4 nonmagnetic phases which evolved as x increased. Scanning electron microscopy (SEM) imaging demonstrated the presence of different phases in the substituted samples, and a general trend of particle-size growth with increasing x. Energy dispersive spectroscopy was used to examine the local stoichiometry of the samples, and confirmed the different phases identified by XRD analysis. The saturation magnetization was found to be high for low substitution level (72 emu/g for the sample with x = 0.1 sintered for 2 h, and 65 emu/g for the sample sintered for 10 h), while it decreased significantly with increasing the substitution level. The coercivity (Hc) for the samples sintered for 2 h was found to decrease sharply with increasing x, even at low substitution levels (x < 0.2), where it decreased from about 3.5 kOe for the un-substituted sample down to about 1.6 kOe for the sample with x = 0.1, and down to below 0.3 kOe at higher substitution levels. The coercivity of the sample with x = 0.1 sintered for 10 h reduced further, down to about 677 Oe, demonstrating properties demanded for magnetic recording applications. Further, washing with HCl was found to remove some of the nonmagnetic phases, and increase the yield of the BaM phase.

Hopkinson peak and superparamagnetic effects in BaFe12-xGaxO19 nanoparticles

In this article, the thermomagnetic properties of a system of Ga-substituted barium hexaferrite nanoparticles (BaFe12-x Gax O19 ) prepared by ball milling were investigated. The thermomagnetic curves for the samples with x ranging from 0.0 to 1.0 exhibited sharp peaks with high magnetization just below T C (Hopkinson peaks). The height of the peak for our samples was similar or larger than previously observed or calculated values. Theoretical treatment of the experimental data demonstrated that the peaks are due to the effect of superparamagnetic relaxations of the magnetic particle. This effect was confirmed by hysteresis measurements at, and just below the temperature at which the peak occurred. Consequently, the particle diameters were calculated from the experimental data using a theoretical model based on the superparamagnetic behavior of a system of uniaxial, randomly oriented, single domain, non-interacting particles. The calculated diameters of 11 – 26 nm are less than the physical diameters determined from TEM measurements. The factors responsible for the low calculated values are discussed.

Structural and magnetic properties of Vanadium Doped M- Type Barium Hexaferrite (BaFe12-xVxO19)

Precursor powders of barium hexaferrite doped with vanadium, BaFe12-xVxO19 with (x = 0.1, 0.2, 0.3, 0.4, 0.5), were prepared using the ball milling technique and then sintered at different temperatures for 2 h. The structural properties of the prepared samples were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), while the magnetic properties were examined by the vibrating sample magnetometry (VSM). XRD and SEM studies of the samples sintered at 1100° C indicated the presence of Ba3V2O8 and α-Fe2O3 non-magnetic oxide phases in addition to BaM hexaferrite phase. The fractions of the nonmagnetic oxide phases were found to increase with increasing x, and sintering the samples at temperatures higher than 1100° C was found to reduce the amounts of these non-magnetic phases only slightly. However, the addition of barium in excess of the stoichiometric ratio was found to remove the α-Fe2O3 oxide, and improve the saturation magnetization of the samples significantly. In addition, washing these samples with HCl was found to improve the saturation magnetization further. The effect of sintering the samples at higher temperatures was also found to reduce the coercivity due to growth of the particle size. However, the coercivity of all samples remained high enough for potential permanent magnet and magnetic recording applications.

Tuning the Magnetic Properties of M-type Hexaferrites

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-particle interactions in the particulate samples was observed.

Structural and Magnetic Properties of Ba3[Cu0.8−xZnxMn0.2]2Fe24O41 Z-Type Hexaferrites

We report on the synthesis and characterization of Ba3[Cu0.8−xZnxMn0.2]2Fe24O41 (x = 0.0, 0.2, 0.4, 0.6, and 0.8) barium hexaferrites. The samples were prepared by high-energy ball-milling technique and double-sintering approach. The effects of Zn substitution for Cu on the structural and magnetic properties of the prepared samples were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). XRD patterns of the samples revealed the presence of a major Z-type hexaferrite phase, together with secondary M-type and Y-type phases. The magnetic results indicated that the saturation magnetization increased slightly with increasing the Zn content, while the coercivity and magnetocrystalline anisotropy field exhibited a decreasing tendency with the increase of Zn content. The thermomagnetic curves revealed the complex magnetic structure of the prepared samples and confirmed that the Curie temperature of the magnetic phases decreased with increasing x as a result of the reduction of the strength of the superexchange interactions.