Sami H. Mahmood

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...

On the static and time-dependent magnetic properties of Fe3O4 fine particles: effect of oxidation

Abstract In this work, the results of static and time-dependent magnetization measurements on three systems of Fe 3 O 4 fine particles are reported. Measurements of the static magnetization were carried out in the temperature range 293 K ≤ T ≤ 423 K , and of the remanent magnetization in the temperature range 5 K ≤ T ≤ 300 K over the period of time 30 s ≤ t ≤ 300 s . The remanent magnetization was found to obey the relation M = C − S 1 n t . Annealing the sample at 250°C was found to increase its magnetic anisotropy constant. The results were analyzed within the context of Neels theory of magnetic clusters.

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.

Mössbauer and X-ray diffraction studies of heat-treated Fe3O4 fine particles

Abstract Samples of Fe3O4 fine particles heated at different temperatures have been studied using Mossbauer spectroscopy and X-ray diffraction. The fresh sample and that heated at 160°C both show superparamagnetic behavior. However, the Mossbauer spectra of samples heated at higher temperatures are all magnetically split. The Mossbauer data with and without the application of ∼ 0.4 T magnetic field perpendicular to the direction of propagation of the γ-rays indicate a gradual conversion of Fe3O4 to γ-Fe2O3 and then to α-Fe2O3 with increasing heating temperature, and a complete conversion to α-Fe2O3 in the sample heated at 550°C. The observed increase in the Bhf with heating temperature is attributed to particle growth. Also, X-ray data indicate particle growth with increasing heating temperature, and partial transformation to α-Fe2O3 in the sample heated at 350°C, and a total conversion in the sample heated at 550°C.

Mössbauer spectroscopy of Al substituted Fe in holmium iron garnet

A Mössbauer spectroscopy study was made on Ho3Fe5-xAlxO12 (x=0.0, 0.05, 0.7). X‐ray diffraction patterns indicate that the samples with x=0.0 and 0.05 have the garnet structure, while the sample with x=0.7 has an additional noncubic structural phase. The room temperature spectrum for samples with x=0.0 and 0.05 consists of two magnetic components corresponding to the octahedral and tetrahedral sites with hyperfine magnetic fields (Bhf) of 50 T and 40 T, respectively. For x=0.7 we observe a new magnetic component with Bhf= 45 T, a reduction in the intensity and broadening of the tetrahedral component, and the evolution of a nonmagnetic central component. These variations are evidently due to the addition of aluminium to the system. At liquid nitrogen temperature the samples with x=0.0 and 0.05 are nearly identical. It was also observed that the increase in Bhf for the octahedral site is smaller than that for the tetrahedral site as the temperature is lowered to 80 K.

Mössbauer spectroscopy of Fe3O4 ultrafine particles

Abstract Mossbauer spectroscopy is used to study a system of Fe3O4 ultra-fine particles at temperatures down to 5 K. The effective magnetic anisotropy constant, K, for the system is calculated using the method based on the superparamagnetic relaxation phenomenon, and that based on collective magnetic excitation model, and the results are 2.6 × 105 and 2.0 × 105 J/m3, respectively. These values are larger than those obtained by others for systems with larger mean diameters, implying a significant size dependence of K.

Mössbauer studies of the ternary substitutional alloys FeAl1-xVx, FeAl1-xMnx

Abstract The Mossbauer spectra at room temperature and at 86 K for the alloy systems FeAl1-xVx and FeAl1-xMnx consisted each of a single unsplit absorption line. This means that both systems keep the CsCl (B2) structure as χ increases and that they remain paramagnetic. The isomer shifts (IS) of the absorption line was found to decrease linearly as χ increases. The variation of the IS with temperature was found to be 5.6 × 10-4 mm/s K for both systems, and independent of χ. The IS for the binary alloys were also deduced: IS(FeAl)=0.29 mm/s, IS(FeV)= -0.16 mm/s and IS(FeMn)= -0.05 mm/s.

Mössbauer and structural studies of Fe0.7−xVxAl0.3 alloys

Abstract We report the Mossbauer and structural studies of the alloy system Fe 0.7− x V x Al 0.3 where x =0, 0.02, 0.06, 0.1, 0.2, and 0.3. X-ray diffraction indicates that all the samples studied have single phase with body center cubic structure. The lattice parameter ( a ) increases with increasing the vanadium concentration. Room temperature Mossbauer studies show magnetic ordering for small values of x and paramagnetic behavior for large values of x . The Mossbauer spectra were fitted by a distribution of magnetic hyperfine fields for small values of x and two singlets were added for large values of x . The relation between the hyperfine field and the isomer shift in the hyperfine field distribution is linear. The average hyperfine field and isomer shift were found to decrease with increasing V concentration. The results are interpreted in terms of local environmental effects on the hyperfine interactions.

Oxidation state of the upper mantle beneath the northwestern part of the Arabian lithosphere

Abstract The Fe3+ contents of spinels from upper mantle lherzolite xenoliths occurring in the Pleistocene alkali basalts of northeast Jordan have been determined using 57Fe Mossbauer spectroscopy at room temperature. The determined Fe3+ fractions were used to calculate oxygen fugacity. The calculated ƒ O 2 -T-P conditions are consistent with derivation of the lherzolite samples from a relatively oxidized source region dominated by CO2 and/or H2O fluid species. Calculated ƒ O 2 s range from 0.5 above to 1.1 log-units below the fayalite-magnetite-quartz (FMQ) buffer. Estimated Fe 3+ Fe total - ratios from microprobe analyses are 2–7% more than those determined from Mossbauer spectroscopy and can shift the computed oxygen fugacity by 0.1 to 0.6 log-units. Pressure and/or temperature does not contribute significantly in the calculated Δƒ O 2 . The average Δƒ O 2 (relative to FMQ) is −0.29 ± 0.4 log-units. This is higher than that reported for western Europe (−0.89 ± 0.58), British Columbia (−1.05 ± 0.3), and eastern Australia (−1.78 ± 0.66).