Microstructural and Mössbauer properties of low temperature synthesized Ni-Cd-Al ferrite nanoparticles

We report the influence of Al3+ doping on the microstructural and Mössbauer properties of ferrite nanoparticles of basic composition Ni0.2Cd0.3Fe2.5 - xAlxO4 (0.0 ≤ x ≤ 0.5) prepared through simple sol-gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray, transmission electron microscopy (TEM), Fourier transformation infrared (FTIR), and Mössbauer spectroscopy techniques were used to investigate the structural, chemical, and Mössbauer properties of the grown nanoparticles. XRD results confirm that all the samples are single-phase cubic spinel in structure excluding the presence of any secondary phase corresponding to any structure. SEM micrographs show the synthesized nanoparticles are agglomerated but spherical in shape. The average crystallite size of the grown nanoparticles was calculated through Scherrer formula and confirmed by TEM and was found between 2 and 8 nm (± 1). FTIR results show the presence of two vibrational bands corresponding to tetrahedral and octahedral sites. Mössbauer spectroscopy shows that all the samples exhibit superparamagnetism, and the quadrupole interaction increases with the substitution of Al3+ ions

The influence of ruthenium on the magnetic properties of gamma-Fe2o3(maghemite)studied by Mossbauer spectrscopy.

Ruthenium-doped gamma-Fe2O3 has been synthesized and examined by x-ray powder diffraction, XANES, EXAFS and by Fe-57 Mossbauer spectroscopy. Ruthenium K-edge x-ray absorption spectroscopy shows that ruthenium adopts a fully occupied octahedral site in the spinel related gamma-Fe2O3 structure as Ru4+. The Fe-57 Mossbauer spectra recorded in the presence of a longitudinal magnetic field of 6 T confirmed the octahedral coordination of the tetravalent ions and canting angles for the Fe3+ ions were determined as 24degrees for those in octahedral sites and 33degrees for those in tetrahedral sites. The Fe-57 Mossbauer spectra recorded in situ from ruthenium-doped gamma-Fe2O3 showed parameters typical of maghemite up to 600 K but with a magnetic hyperfine field distribution suggesting an inhomogeneous distribution of ruthenium within particles of varied size around about 15 nm. At 700 K a phase transition from gamma-Fe2O3 to alpha-Fe2O3 was observed and further studies showed the ruthenium-doped alpha-Fe2O3 to have a Morin transition temperature of about 400 K

Tin- and titanium-doped y-Fe2O3

2.5% and 8% tin- and 8% titanium-doped gamma -Fe2O3 have been synthesized and examined by x-ray powder diffraction, EXAFS, electron microscopy and by Fe-57- and Sn-119-Mossbauer spectroscopy. The Sn- and Ti-K-edge EXAFS show that both tin and titanium adopt octahedral sites in the spinel related gamma -Fe2O3 structure. However, whereas tin substitutes for iron on one of the fully occupied sites, titanium adopts the octahedral site, which is only partially occupied. The Fe-57-Mossbauer spectra recorded in the presence of a longitudinal magnetic field of 2-8 T confirm that the tetravalent ions adopt the octahedral sites. The canting angles for both sublattices in gamma -Fe2O3 were determined from the in-field Mossbauer spectra. The Sn-119-Mossbauer spectra showed that the maximum hyperfine field sensed by the Sn4+ ions in gamma -Fe2O3 is about 2/3 of that observed in tin-doped Fe3O4 (magnetite)

Grain size effect on the phase transformation temperature of nanostructured CuFe2O4

We report a large decrease in tetragonal to cubic phase transformation temperature when grain size of bulk CuFe2O4 is reduced by mechanical ball milling. The change in phase transformation temperature was inferred from in situ high temperature conductivity and x-ray diffraction measurements. The decrease in conductivity with grain size suggests that ball milling has not induced any oxygen vacancy while the role of cation distribution in the observed decrease in phase transformation temperature is ruled out from in-field Fe-57 Mossbauer and extended x-ray absorption fine structure measurements. The reduction in the phase transformation temperature is attributed to the stability of structures with higher crystal symmetry at lower grain sizes due to negative pressure effect. (C) 2011 American Institute of Physics. doi: 10.1063/1.3493244

Ferrimagnetic Ordering In Nanostructured Zinc Ferrite

Recent investigations of nanocrystalline ZnFe2O4 have suggested that the cation distribution in this material is partially inverted and this gives rise to scope for potential technological applications [1. T. Sato, K. Haneda, M. Seki and T. Iijima. Appl. Phys. A. 50 (1990), p. 13. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (96)1]. In view of this a considerable amount of research has been done to investigate the effect of grain size on the cation distribution and magnetic properties of nanocrystalline ZnFe2O4. All these studies agree in one aspect that ZnFe2O4 is magnetically ordered with high ordering temperature and large magnetic moment. But they differ in predicting the type of magnetic ordering [2, 3, 4, 5 and 6]. In order to confirm the type of magnetic ordering and to study the effect of grain boundary and surface spins on the magnetic properties of nanostructured ZnFe2O4, we have carried out Mössbauer and magnetisation studies on nanostructured ZnFe2O4 with various grain sizes prepared by ball milling technique

Magnetic properties of nanostructured ferrimagnetic zinc ferrite

Nanostructured ZnFe2O4 ferrites with different grain sizes were prepared by high energy ball milling for various milling times. Both the average grain size and the root mean square strain were estimated from the x-ray diffraction line broadening. The lattice parameter initially decreases slightly with milling and it increases with further milling. The magnetization is found to increase as the grain size decreases and its large value is attributed to the cation inversion associated with grain size reduction. The Fe-57 Mossbauer spectra were recorded at 300 K and 77 K for the samples with grain sizes of 22 and 11 nm. There is no evidence for the presence of the Fe2+ charge state. At 77 K the Mossbauer spectra consist of a magnetically ordered component along with a doublet due to the superparamagnetic behaviour of small crystalline grains with the superparamagnetic component decreasing with grain size reduction. At 4.2 K the sample with 11 nm grain size displays a magnetically blocked state as revealed by the Mossbauer spectrum. The Mossbauer spectrum of this sample recorded at 10 K in an external magnetic field of 6 T applied parallel to the direction of gamma rays clearly shows ferrimagnetic ordering of the sample. Also, the sample exhibits spin canting with a large canting angle, maybe due to a spin-glass-like surface layer or grain boundary anisotropies in the material

Synthesis, structure and properties of a semivalent iron oxoborate, Fe₂OBO₃

Transition metal oxoborates are of interest for magnetic and optical properties. Crystals of many MII2MIIIO2BO3 and MIIMIIIOBO3 materials can be grown from borate fluxes. In the FeII–FeIII–B–O system, flux growth results in Fe3O2BO3 crystals, but solid state reaction at higher temperatures has yielded Fe2OBO3 as a polycrystalline powder. This has been characterised by synchrotron and neutron diffraction, electron microscopy, Mossbauer spectroscopy, and conductivity and magnetic measurements. Two notable transitions occur, a broad semiconductor– semiconductor change accompanied by a structural transition at 317 K, and L-type ferrimagnetic order below a Curie temperature of 155 K. An average (Fe2+)0.5(Fe3+)0.5 valence is observed at the two crystallographically distinct sites in Fe2OBO3, indicating that charge ordering occurs

Neel temperature enhancement in nanostructured nickel zinc ferrite

The Neel temperature of Ni0.5Zn0.5Fe2O4 spinel ferrite increases significantly from 538 K in the bulk state to 592 K when the grain size is reduced to 16 nm by milling in a high-energy ball mill. This has been attributed to an increase in the AB superexchange interaction strength due to a possible enhancement in the magnetic ion concentration in the A-site on milling, as is evident from extended x-ray absorption fine structure and in-field Mossbauer measurements. (c) 2005 American Institute of Physics