Synthesis, structural and magnetic characterisation of the double perovskite A 2MnMoO 6 (A=Ba, Sr (original) (raw)
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Synthesis, Structural, and Magnetic Characterization of Mn 1− x Ni x Fe 2 O 4 Spinel Nanoferrites
… and Novel Magnetism, 2011
A study of the crystallographic structure and magnetic properties of the double perovskites Ba 2 MnMoO 6 and Sr 2 MnMoO 6 in polycrystalline form has been carried out by means of neutron powder diffraction (NPD) and magnetization measurements. The Rietveld analysis of room temperature data shows that the Mn 2+ and Mo 6+ ions are B-site ordered, i.e. the structure is a NaCl-type ordered double perovskite. Ba 2 MnMoO 6 crystallizes in the cubic space group Fm3m (a = 8.1680(1)) and Sr 2 MnMoO 6 crystallizes in the space group P4 2 /n (a = 7.9575(5), c = 7.9583(9)). Bond valence sum (BVS) calculation revealed that these compounds have the valency pair of {Mn 2+ (3d 5 ;t 3 2g e 2 g ), Mo 6+ (4d 0 )}. The magnetic measurements suggest that these compounds transform to an antiferromagnetic state below 10 K.
International Journal of Nanoparticles, 2016
Nanoferrite powders having composition Mn x Mg 1-x Fe 2 O 4 (x = 0.0, 0.2, 0.4, 0.6, 0.8) were synthesised by the chemical co-precipitation method and then sintered as the pellets. The X-ray diffraction (XRD), Alternating Gradient Force Magnetometer (AGFM) techniques and Curie temperature measurement were used to carry out this study. The XRD patterns confirm the nanosized dimension of the samples and showed that the samples are single phase cubic spinel nanoferrites. From the analysis of XRD data using Scherrer's formula, the average crystallite size (D XRD) of the particles was found to decrease from 81 to 55 nm with increasing manganese substitution. Substitution of Mn 2+ in MgFe 2 O 4 causes an increase in the lattice constant (a) from 8.35 to 8.43 Å. The magnetic parameters such as saturation magnetisation (M S), coercivity (H C) and remanence (M r) with increasing Mn 2+ concentration are studied at room temperature by an AGFM. Substitution of Mn 2+ for Mg 2+ increased M S from 21.2 to 74.7 emu g-1 and decreased H C from 23 to 10 Oe and decreased Curie temperature from 392 to 294°C.
A B S T R A C T Co-precipitated and 800 °C heat treated Ni-Cu-Zn nanoferrites with chemical formula Ni x Cu 0.1 Zn 0.9-x Fe 2 O 4 (x=0.5, 0.6, 0.7) were prepared because of their potential use as multilayer chip inductors in electromagnetic applications. Their structural, magnetic properties and phase formation were studied using X-ray diffractometer (XRD), field emission scanning electron microscope (FE–SEM), vibrating sample magnetometer (VSM), Mössbauer spectrometer, thermogravimetric analyzer (TGA) and differential scanning calorimeter (DSC). The XRD patterns confirm the cubic spinel structure of the ferrite phase belonging to Fd3m space group. Lattice parameters and cation distributions were obtained by Rietveld refinement of the XRD patterns. The lattice parameter decreases with increase in Ni 2+ ion concentration. Rietveld analysis indicates that Cu 2+ ions predominantly occupy the B-sites and Ni 2+ ions partly going into B-sites but predominantly into A-sites. An excellent agreement is observed between the experimental lattice parameters and lattice parameters theoretically calculated using this cation redistribution. The inversion parameter (λ) observed for Fe 3+ ions by Mössbauer spectroscopy is different from that of Rietveld analysis. Magnetization and Mössbauer spectro-scopic measurements indicate that the ferrite nanoparticles are mostly superparamagnetic. The cation redistribution is supposed to alter the magnetocrystalline anisotropy which in turn affects the magnetic parameters of the present ferrite samples. The reduced magnetization is attributed to core-shell interactions and possible canting of A-and B-shell magnetizations. TGA-DSC studies indicate that ferrite formation in the 800 °C heat treated samples is completed but grain growth increases as the particles are subject to the increased temperature.
Lanthanum calcium ferrite La 1−x Ca x FeO 3 (where x = 0.05, 0.10 and 0.15) were synthesized by co-precipitation method. The structural refinement confirmed that all samples formed with the orthorhombic (Pbmn) structure with small impurities (LaFeO 3 and Fe 2 O 3 ). Fourier transformed infrared spectroscopy (FT-IR) results indicated that the electronic imbalance caused by the partial substitution for La 3+ by Ca 2+ is compensated by an oxidation state of iron ions. Mössbauer spectra at room temperature (RT) show five 6-line sub-spectra corresponding to Fe 3+ (superposition of 3 spectra), Fe 4+ and Fe 5+ in all samples. Magnetic hysteresis loops of these samples showed a significant weak ferromagnetic component at RT.
A B S T R A C T Polycrystalline nanoferrites with chemical formula Mg x Zn 1−x Fe 2 O 4 (x=0.5, 0.6, 0.7) have been synthesized by co-precipitation technique and then subsequently heated to 800 °C in order to investigate structural, thermal and magnetic properties. The samples are characterized by using XRD, FTIR, TGA-DSC, SQUID and Mössbauer spectroscopy techniques. The synergic effect of heat treatment with substitution of Mg 2+ , results in random variation of lattice parameter (a) and crystallite size (D). FTIR studies revealed the formation of cubic spinel structure. The broadening at octahedral bands for compositions x=0.6 and 0.7 attributes to distribution of ferrite particles of different sizes in these samples. The characteristic feature of hysteresis loops reflects the nature of ferrite particles in the state of superparamagnetism. The saturation magnetization at room temperature has been reported for composition x=0.7 is 44.03 emu/g. The variation of coercivity is due to variation in magnetic anisotropy which is predominately affected by the exchange interactions arising from the nature of nanoparticles. The blocking temperatures are in the range of 10–30 K and their variation is in the line of change in magnetocrystalline anisotropy but not due to variation in crystallite sizes. The Zeeman splitting at tetrahedral (A) and octahedral (B) sites for composition x=0.6 is expected due to increase in size of core of the nanoparticles/or increasing of magnetocrystalline anisotropy. The range of isomer shift values and quadruple splitting values are evident for the presence of Fe 3+ ions and the absence of Fe 2+ ions in the present systems. The present ferrite nanoparticles in the superparamagnetic state are the potential candidates for biomedical applications like cancer treatment through hyperthermia. The results are interpreted in terms of cation redistribution presuming exchange coupling energy variation on magnetocrystalline anisotropy.
Advances in Applied Ceramics, 2012
Ceramics materials of the class of spinel nanoferrites of Mn 12x Ni x Fe 2 O 4 (x50?00, 0?025, 0?50, 0?75 and 1?00) of 13-25 nm particle sizes have been investigated for their electrical and dielectric characteristics. The dc electrical resistivity was measured and found to decrease with an increase in x to follow the Verwey mechanism because of the increase in electron hopping between the Fe 2z tetrahedral site (A site) and the Fe 3z octahedral site (B site). In addition, the resistivity of ferrites was observed to decrease with an increase in temperature, confirming their semiconductor characteristics. The dielectric constant and the dielectric loss factor were found to decrease as the frequency increased, following the Maxwell-Wagner interfacial type of polarisation. The study of the electrical properties of the prepared ferrites suggests their usefulness in important applications in electronic devices in reducing power losses due to an increase in conductivity caused by the increment in Ni concentrations in various electronic circuitries, such as those in computers and transformer coils.
Journal of Superconductivity and Novel Magnetism, 2012
Mn 0.5 Co 0.5 Fe 2 O 4 nanosized ferrites have been made directly from MnFe 2 O 4 and CoFe 2 O 4 ferrites and from metal oxides by using high-energy ball milling. Singlephase formation and microstructure of the as-milled samples and samples annealed at 100, 200, 300, 400 and 500 • C under argon atmosphere were studied using powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The average grain sizes were estimated from XRD measurements and found to be between 7 and 11 nm. The microstrain for each sample was relieved by annealing due to crystallite growth. Room temperature magnetic properties were investigated by zero-field 57 Fe Mössbauer spectroscopy and vibrating sample magnetometer (VSM). Saturation magnetizations of the samples were estimated using the empirical law of approach to saturation. The variation of coercive field, saturation magnetization, maximum magnetization and remanent magnetization for each sample was found to depend on the annealing temperature. The coercive fields are observed to increase with increased annealing temperature (from about 300 Oe for the as-milled samples to about 1000 Oe for samples annealed at 500 • C) which we attribute to increases in grain sizes.
Structural and magnetic properties of MgxSrxMnxCo1-3xFe2O4 nanoparticle ferrites
2013
A series of MgxSrxMnxCo1-3xFe2O4 nanoferrites (with x =0, 0.1, 0.2, 0.3, 1/3) were synthesized by glycol-thermal technique. X-ray diffraction (XRD) patterns of the as-prepared samples show single-phase cubic spinel structure. The average crystallite sizes, lattice parameters, XRD densities and porosities were estimated from XRD data. The average crystallite sizes were found in range of 7.5 to 9 nm. Mössbauer spectroscopy measurements were performed in order to investigate the magnetic order of the materials and the distribution of Fe ions in the tetrahedral and octahedral sites. Room temperature magnetic measurements of the series were studied using a vibrating sample magnetometer. The results show that the values of the coercive fields and saturation magnetizations which increase with increase in Co content from 15 Oe and 56.51 emu/g for x=0.3 to 114 Oe and 76.61 emu/g for x= 0.1 respectively. Significant correlations between magnetizations and coercive fields are observed. A signi...
Journal of Magnetics, 2014
Ni 0.6 Zn 0.4 Fe 2 O 4 prepared using solid state reaction and sol-gel methods were compared for their structural and magnetic properties. Due to the much higher annealing temperature used in solid state reaction, the crystalline size was much larger than that of the nanoparticles prepared by sol-gel. The saturation magnetization of sol-gel nanoparticles was higher, and the coercivity was about 2 times larger, compared to the solid state reaction sample. By analyzing the integration intensity of x-ray diffraction peaks (220) and (222), we proposed that the difference in the saturation magnetization might be due to the inversion of cation distribution caused by the different preparation techniques used.