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We report on the synthesis of spinel Co1-xZnxFe2O4 (x=0.0-0.56) ferrites by sol-gel auto-combustion method. X-ray diffraction 'XRD', magnetic measurements were used to study compositional-dependence of structural, magnetic properties, connection among them. Mössbauer spectroscopy was used to identify non-magnetic-phase, its effect on magnetic properties. Single-phased nano spinel-ferrite formation is confirmed by XRD. Increasing Zn-content leads to structural modifications such as decrease of lattice parameter, grain diameter DW-H, alteration of inversion parameter, disorder, tensile-strain, dislocation density, variation of A–O–B, A–O–A, B–O–B super-exchange-interaction and canting angles. Cationic distribution suggests that Fe3+,Co2+ ions reside on both A, B-sites, and with increasing Zn-content, B-site population of Fe3+, Zn2+ ions increases; while that of Co2+ ions decreases. Saturation magnetization shows noticeable dependence on canting angle suggests that the magnetization in the studied samples is described by Yafet-Kittel three-sub-lattice model. Coercivity Hc values are consistent with anisotropy, and its dependence on DW-H suggests that the studied samples are inoverlap-region between multiple-domains/single-domain. Reduced-remanence indicate the variation of inter-grain magnetostatic-interaction, isotropic-behavior of multi-domain particles. Observed broad peaks in magnetization derivative with field suggest large-number of dislocations, more-uniform particle-size. Switching-field-distribution proposes potential application of the studied x=0.0 sample in high density recording, and sample with x=0.56 in targeted drug delivery. Mössbauer measurements confirm three-magnetic-components corresponding to A,B-sites, Fe3+ ions in grain boundaries/surface, Fe has 3+ oxidation state, and growing paramagnetic-doublet, alone does not explain the trend of Ms, suggesting that it is a collective-effect of structural-modification, presence of paramagnetic-doublet. [ABSTRACT FROM AUTHOR]

In the present work, we report the preparation and study of tin (Sn) substituted polycrystalline HfO2, which is known for its fascinating ferroelectric properties. Hf1-xSnxO2 (x=0 to 0.1) are prepared by conventional solid state reaction method and characterized by x-ray diffraction (XRD), Raman spectroscopy, 119 Sn Mössbauer spectroscopy and dielectric / ferroelectric measurements. XRD of all the samples is analyzed considering P21/c (monoclinic) space-group, however less intense un-reacted SnO2 peaks were observed for x ≥ 3% substitution. Raman spectra of all the samples is observed to be characteristic of P21/c phase. The 119 Sn Mössbauer spectra show a broad absorption line and the obtained hyperfine parameters are more or less same for all the compositions studied, within the experimental error, indicating the presence of parent P21/c phase with Sn substitution. No switchable polarization is observed from bulk ferroelectric measurements, corroborating the observed XRD, Raman and Mössbauer results i.e., the presence of only P21/c (monoclinic) phase. The present results are discussed in the context of recent theory works in HfO2. [ABSTRACT FROM AUTHOR]

In this work, we studied atomic self-diffusion and structural phase transformation in a single phase iron mononitride (FeN) thin film deposited at an optimized substrate temperature (Ts) of 423 K. At this Ts, the FeN film exhibits a tetrahedral coordination between Fe and N atoms (ZnS-type structure with a lattice parameter of 4.28 Å). The structure of the FeN film was studied by combining x-ray diffraction with Fe and N K-edge x-ray absorption spectroscopy and conversion electron Mössbauer spectroscopy measurements. Self-diffusion of Fe and N was measured using secondary ion mass spectroscopy depth profiling in trilayer structures: [FeN(50 nm)/ 57 FeN(2 nm)/FeN(50 nm)] and [FeN(50 nm)/Fe 15 N(2 nm)/FeN(50 nm)] deposited on an amorphous quartz substrate using reactive magnetron sputtering. It was found that atomic self-diffusion is strongly associated with thermal stability. Before reaching the phase decomposition temperature, the self-diffusion of N was found to be slower than Fe. Upon phase decomposition, both Fe and N diffuse rapidly, and at this stage, the self-diffusion of N takes over Fe. Within the thermally stable state, slower N diffusion indicates that Fe–N bonds are stronger than Fe–Fe bonds in FeN. This behavior was predicted theoretically and has been evidenced in this work. [ABSTRACT FROM AUTHOR]

We report on the synthesis of spinel Co1-xZnxFe2O4 (x=0.0-0.56) ferrites by sol-gel auto-combustion method. X-ray diffraction 'XRD', magnetic measurements were used to study compositional-dependence of structural, magnetic properties, connection among them. Mössbauer spectroscopy was used to identify non-magnetic-phase, its effect on magnetic properties. Single-phased nano spinel-ferrite formation is confirmed by XRD. Increasing Zn-content leads to structural modifications such as decrease of lattice parameter, grain diameter DW-H, alteration of inversion parameter, disorder, tensile-strain, dislocation density, variation of A–O–B, A–O–A, B–O–B super-exchange-interaction and canting angles. Cationic distribution suggests that Fe3+,Co2+ ions reside on both A, B-sites, and with increasing Zn-content, B-site population of Fe3+, Zn2+ ions increases; while that of Co2+ ions decreases. Saturation magnetization shows noticeable dependence on canting angle suggests that the magnetization in the studied samples is described by Yafet-Kittel three-sub-lattice model. Coercivity Hc values are consistent with anisotropy, and its dependence on DW-H suggests that the studied samples are inoverlap-region between multiple-domains/single-domain. Reduced-remanence indicate the variation of inter-grain magnetostatic-interaction, isotropic-behavior of multi-domain particles. Observed broad peaks in magnetization derivative with field suggest large-number of dislocations, more-uniform particle-size. Switching-field-distribution proposes potential application of the studied x=0.0 sample in high density recording, and sample with x=0.56 in targeted drug delivery. Mössbauer measurements confirm three-magnetic-components corresponding to A,B-sites, Fe3+ ions in grain boundaries/surface, Fe has 3+ oxidation state, and growing paramagnetic-doublet, alone does not explain the trend of Ms, suggesting that it is a collective-effect of structural-modification, presence of paramagnetic-doublet. [ABSTRACT FROM AUTHOR]

FexCo100−x nanoparticles with different stoichiometry ($x = 0$ –100) have been prepared by a facile synthesis process and compositions confirmed using X-ray fluorescence spectroscopy. X-ray diffraction measurements suggest alloy formation in the body-centered cubic (BCC) phase, with a progressive shift of peak positions to account for the stoichiometric changes. The evolution of nanoparticle morphology is from cubic for iron to hexagonal for cobalt, and the entire composition range has been examined. Magnetic behavior has been accessed by Mössbauer spectroscopy and vibrating sample magnetometric measurements, which suggests an increase of magnetization values of iron upon alloying with cobalt. A detailed account of the synthesis scheme has been presented, to achieve uniform alloy nanoparticles in the pristine state with minimum aggregation and surface oxidation, by carefully adjusting the reaction timescales. [ABSTRACT FROM AUTHOR]

This work reports honey green synthesis of MgxZn1-xFe2O4 (x = 0.0–1.0) spinel nano ferrite (grain diameter: 25.3 nm- 33.4 nm) by sol–gel auto-combustion method. Thermally treated samples at 550 °C for 3 h, were characterized by x-ray diffraction, 'XRD' scanning-electron-microscopy-energy-dispersive-x-ray-spectroscopy 'SEM-EDS', Mössbauer spectroscopy operating at 5 K with/without 5 T magnetic field. XRD confirms spinel phase formation, and presence of α-Fe2O3 (1.1–4.2%), while EDS confirms the uniform allocation of all the elements present in the studied samples. Agglomerated nano-particles are seen in SEM images. Increasing Mg-content: i) alters structural properties, ii) leads to modification of cationic population on A, B site, iii) affects A–O–A, B–O–B, A–O–B super-exchange interaction, and iv) shows linear decrease of Néel magnetic moment. Mössbauer results confirms 3+ state of Fe, and changes in local environment around Fe3+ ion induced modification of super-exchange interaction, reflected in internal hyperfine field. Finite canting angle suggests the applicability of Yafet-Kittel (Y-K) three sub-lattice model in describing magnetic behavior of the studied samples. Due to the presence of α-Fe2O3 in the studied samples, difference is observed in the inversion parameter, obtained from XRD, and Mössbauer data. [ABSTRACT FROM AUTHOR]

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We report sol gel auto-combustion synthesized CoCrxFe2-xO4 (x = 0.0 − 1.0) spinel ferrites, and use x-ray diffraction 'XRD', magnetic measurements, and Mössbauer spectroscopy to study the effect of Cr-content on their structural properties, magnetic properties, and correlation between them. Formation of single-phase nono spinel ferrite (grain size: 18.1 – 46.6 nm), is confirmed by XRD. Results show that with increasing Cr-content, lattice parameter decreases, and Cr3+ ions remain more populated on B-site, whereas Co2+ ions remains almost equally populated on both A, B site, show lower disorder, and modification of A–O − A, B– O − B, A–O − B super-exchange interaction. For Cr-content ≥ 0.75, Mössbauer measurements show presence of a non-magnetic doublet, and isomer shift values confirm that Fe has 3 + oxidation state. Observed structural changes, lead to reduction of saturation magnetization, coercivity. [ABSTRACT FROM AUTHOR]

The present work reports the in-field 57Fe M ö ssbauer spectroscopy measurements on polycrystalline R3Fe5O12 (RIG, R=Y, Gd, Ho, Tm, & Yb) rare-earth iron garnets. The contrast between the effective hyperfine field (Heff) values of two Fe3+ sites (tetrahedral, d- and octahedral, a- sites) across magnetic compensation (TComp) facilitates to probe the Fe3+ sublattice spin reversal in RIG systems (R=Gd, Ho and Yb) exhibiting magnetic compensation. Further, the analysis of relative intensity of absorption lines in a sextet from the field dependent 57Fe M ö ssbauer spectroscopy measurements carried out in polycrystalline YbIG, below TComp, show the clear signatures of field induced perpendicular Fe3+ spin configuration when applied external field is 50 kOe. [ABSTRACT FROM AUTHOR]

In the present work, polycrystalline Y-type Ba0.5Sr1.5Co2−xZnxFe12O22 (X = 0, 0.5, 1 & 2) hexa-ferrites prepared by the sol-gel auto combustion method are investigated by x-ray diffraction (XRD), 57Fe Mössbauer spectroscopy (MS) and magnetization measurements. XRD data confirms the single-phase formation for x = 0 and 0.5; however, with further increase in Zn concentration secondary phases are observed. The in-field Mössbauer data measured at low temperature (5K) indicates that there is a re-distribution of Fe3+ ions in the studied samples, with the substituted Zn2+ preferentially going to 6CIV, 6CIV ∗ sites. [ABSTRACT FROM AUTHOR]

The present work reports the study of transcritical state of magnetic anisotropy in FexNi100-x films as a function of film thickness and composition. The transcritical state is a manifestation of weak perpendicular magnetic anisotropy resulting in peculiar hysteresis loop and stripe magnetic domains above a critical thickness of film. Signatures of transcritical state, corroborated by the formation of stripe domains, are observed in the magneto optical Kerr effect(MOKE) data and magnetic force microscopy (MFM) data of FexNi100-x films with ≈ 75 nm thickness for x = 7. The effect of thickness on the formation of transcritical state is studied for Fe9Ni91 films and it is observed that films with thickness ≥ 105 nm exhibit transcritical state. Further a quantitative analysis of magnetic texture is carried out by 57Fe conversion electron Mössbauer spectroscopy (CEMS) measurements for the thickness variation samples. The CEMS data show a systematic variation in the area ratio of second and third line intensity as a function of thickness corroborating the MOKE data. The films are studied as a function of thermal annealing and it is observed that the transcritical state still preserved for Fe9Ni91 films of higher thickness even after annealing at 300 ∘C. [ABSTRACT FROM AUTHOR]

In the present work polycrystalline composites consisting of soft and hard ferrimagnetic phases with compositional formula (NiFe2O4)100-x – (BaFe12O19)x (x = 0,20,40,50,60,80,100) have been synthesized by sol-gel method. Thus formed materials were calcined at 1000 °C for 2 h and sintered in a microwave furnace at 1200 °C for 30 min. These composites were characterised structurally by X-ray diffraction studies and morphological studies were done using scanning electron microscopy (SEM). Analysis of XRD data confirmed hexagonal structure with P63/mmc space group for Barium hexaferrite (BFO) and cubic structure with Fd-3 m (227) space group for Nickel ferrite (NFO). Mössbauer spectroscopy measurements were also done for the selected samples and the data is analysed to extract the hyperfine parameters of both the soft magnetic and hard magnetic phases and the results are used to corroborate the observed magnetic properties. [ABSTRACT FROM AUTHOR]

The present work reports the structural, electrical and magnetic properties of W6+ and Mo6+ substituted four-layer Aurivillius compound, Bi5FeTi3O15 (BFTO). The oxidation states of the dopants and other elements of BFTO are studied from x-ray photo-electron and 57Fe Mössbauer spectroscopy. The substitution resulted in a net increase of magnetic cation (Fe3+) from 25% to about 37.5% in BFTO. However, the magnetization measurements indicate the lack of magnetic ordering even down to 2 K. Further, the high temperature (300-1070 K) dielectric study of these compounds reveal the ferroelectric transition temperature decreases with the increase of magnetic cations in BFTO because of hexavalent W6+ and Mo6+ substitution at Ti4+ site. [ABSTRACT FROM AUTHOR]

Fe/Al multilayer thin films with an overall atomic concentration ratio of Fe:Al=1:2 have been prepared by ion-beam sputtering. Phase formation and microstructural evolution with thermal annealing have been studied by x-ray reflectivity, cross-sectional transmission electron microscopy, dc magnetization, and conversion electron Mössbauer spectroscopy. These studies show that although the starting composition is Al rich, the intermixing of Fe and Al at the interfaces leads to the formation of a magnetic Fe3Al-like region at the interface. Thus, the magnetic contribution in the as-deposited multilayer structure (MLS) is not only from pure Fe but also from an Fe3Al-like region formed at the interface. On annealing the MLS, a stable nonmagnetic MLS consisting of intermetallic B2 Fe50Al50 separated by thin Al layers is formed. Further annealing only induces better ordering of Fe50Al50 and does not destroy the MLS. [ABSTRACT FROM AUTHOR]

The present work reports preparation of polycrystalline G d F e 1 − x M n x O 3 (x = 0.0 to 0.5) samples with solid-state reaction method and characterization using x-ray diffraction, 57 Fe Mössbauer spectroscopy, magnetization measurements, leakage current density and soft x-ray absorption spectroscopy measurements. Although F e 3 + and M n 3 + have similar ionic radii, noticeable variations in lattice parameters are seen which are attributed to local distortions introduced by Jahn-Teller active M n 3 + doping. Antiferromagnetic transition temperature corresponding to F e 3 + ordering ( T N , F e ) and G d 3 + ordering ( T N , G d ) is found to decrease with Mn doping, which could be due to weakening of Fe-Fe interaction and Gd-Gd interactions respectively. The Mn substitution at Fe site in G d F e O 3 is found to induce F e 3 + spin reorientation transition ( T S R T ) at a critical concentration and T S R T is found to increase with the Mn doping. Temperature dependent 57 Fe Mössbauer measurements have been carried out to study the local distortions by estimating quadrupole shift, the evolution of magnetism and also the spin reorientation transition in G d F e O 3 with Mn doping. Leakage current density is found to increase with Mn doping in G d F e O 3 , initially very fast and almost saturating for higher concentrations of Mn doping due to the formation of multiple oxidation states of dopant Mn at lower concentrations as evidenced from soft x-ray absorption spectroscopy measurements. [ABSTRACT FROM AUTHOR]

The present work reports the preparation of polycrystalline multiferroic G d F e O 3 (GdFO) and characterization with x-ray diffraction (XRD), magnetization, temperature dependent Raman spectroscopy, temperature and magnetic field dependent F 57 e Mössbauer spectroscopy measurements. The sample is found to be phase pure from Rietveld refinement of XRD pattern. The Mössbauer spectra measured in the presence of external magnetic field show the signatures of field induced spin reorientation transition, which are corroborated by magnetization measurements. From the temperature dependent variation of internal hyperfine field, Neel transition temperature ( T N , F e ) of 672.5 ± 0.2 K and critical exponent ( β ) of 0.333 ± 0.003 is obtained. Temperature dependent (300–760 K) Raman spectroscopy measurements show the signatures of spin-phonon coupling and local structural re-arrangement across T N , F e . [ABSTRACT FROM AUTHOR]

We report on the magnetic and Mössbauer properties of polycrystalline HoFe 1- x Cr x O 3 (0≤ x ≤1) compounds. Magnetization data reveals the continuous tailoring of magnetic transition due to weakening of Ho 3+ -Fe 3+ and Fe 3+ -Fe 3+ interactions in the entire temperature range by replacing the Fe 3+ ions with Cr 3+ ions. The observed decrease in Néel temperature (T N ) and increase in spin re-orientation transition temperature (T SR ) with the replacement of Fe 3+ with Cr 3+ is ascribed to the weakening of Fe(Cr)-O-Fe(Cr) antiferromagnetic exchange interaction. In addition, we also attribute such a change in T N to the enhancement of ferromagnetic interaction of adjacent Cr 3+ moments through t - e hybridization as a result of the structural distortion. The decrease in isomer shift (IS) suggests enhancement of the interaction between nuclear charge with the 3 s electrons as a result of decrease in radial part of 3 d wave function with Cr addition. In this paper we also discuss about the variation of quadrupole splitting (QS) and hyperfine fields (H hf ) with Cr addition in HoFe 1- x Cr x O 3 (0≤ x ≤1) compounds. [ABSTRACT FROM AUTHOR]

Temperature dependence of magnetization, anisotropy, and hyperfine interaction parameters of NiFe2–xYbxO4 ( $x = 0$ , 0.05, and 0.075) was investigated, and the results are presented. All the compounds were prepared by solid-state reaction formed in cubic inverse spinel phase with the space group $Fd\overline 3 m$ . Increments in the lattice constant were observed upon partial substitution of Fe3+ by Yb3+. Decreased magnetic moment and increased magnetic anisotropy with Yb3+ substitution were observed through magnetization measurements, carried out at 5, 100, 200 and 300 K. Analyses of Mössbauer spectra recorded at 5 K and 300 K, revealed decreased hyperfine fields and magnetic moments at the B-site (and hence net moment) with increasing Yb3+ content. In addition all the compounds exhibited Neel-type, collinear ferrimagnetic structure. [ABSTRACT FROM PUBLISHER]

CuCoZnFeO nanoparticles were prepared by a co-precipitation method and the size was varied by varying annealing temperatures. The cation distribution, estimated using Mössbauer spectroscopy, shows that it is the same for all samples, irrespective of the size. The variation of Curie temperature and saturation magnetization as a function of particle size, studied using d.c. magnetization, clearly indicates that these are a result of finite size scaling effects. The superparamagnetic size limit is estimated to be 8 nm. [ABSTRACT FROM AUTHOR]

The nanoparticles of spinel ferrites having composition NiCaFeO were synthesized by an advanced sol-gel method and subsequently coated with intrinsically conducting polypyrrole (PPy) by chemical oxidative polymerization of the corresponding monomer (pyrrole) using ammonium peroxodisulphate as oxidant. The X-ray diffraction and TEM measurements were obtained to understand the crystalline structure, size and morphology of evolution of the samples. The dc electrical investigation revealed that at room temperature the surface conductivity increased from 2.8×10 S cm to 1.5×10 S cm on polymerization. Mössbauer investigations revealed that the polymerization causes migration of Fe ions from A to B site, resulting to the enhancement of the observed hyperfine field. In agreement with this, the dc magnetization measurements performed on VSM revealed an enhancement in saturation magnetization in the M- H curves on polymerization. The value of blocking temperature ( T) is found to have credibly increased from 110 K to 130 K, which confirms the increase in crystallite size after polymerization. [ABSTRACT FROM AUTHOR]

Spinel nanoferrites of composition Ni0.4Ca0.6Fe2O4 have been synthesized by sol-gel method and subsequently coated with intrinsically conducting polymers such as polyaniline and polypyrrole separately, using chemical oxidative polymerization technique. The characterization of the composites has been performed by X-ray diffraction and atomic force microscopy images. The room temperature DC electrical conductivity measurements are performed in order to understand the coating effectiveness and the nature of electrical conductivity of the composites. The Mössbauer spectroscopic studies reveal that the ferrimagnetic as well as super-paramagnetic states co-exist at room temperature (300 K) for all the samples which is found in good agreement with the DC magnetization measurement results, wherein the coercivity is observed in the M-H curves for all the samples at room temperature. [ABSTRACT FROM AUTHOR]

Nano nickel-zinc-indium ferrite (NZIFO) (Ni0.58Zn0.42InxFe2-xO4) particles with varied quantities of indium (x = 0, 0.1, 0.2) have been chemically synthesized through a reverse micelle reaction and investigated by X-ray diffraction, transmission electron microscopy and by magnetic and Mossbauer spectral studies. The dependence of Mossbauer parameters, viz, isomer shift, quadrupole splitting, linewidth and hyperfine magnetic field on In3+ concentration have been discussed. Mossbauer results are also supported by magnetization data. With these interesting ferromagnetic properties indium substituted nano nickel-zinc ferrites have potential applications in magnetic storage data. The dependence of Mossbauer parameters on nano NZIFO particles at 5 K and 300 K has been studied. The values of Bloch exponent (α) are in well accordance with that reported for bulk materials. [ABSTRACT FROM AUTHOR]

Fe-doped polycrystalline samples La0.67Ca0.33Fe x Mn1 − x O3 ( x = 0%, 5%, 7.5%, 10% and 15%) are studied employing 57Fe Mössbauer effect measurements. The room temperature Mössbauer measurements of all the samples indicate the presence of Fe + 3 state and it is observed that the quadrupole splitting remains constant up to 10% Fe doping and increases with 15% Fe doping. Resistivity data shows increasing insulating behaviour with Fe doping and insulating region follows Efros–Shlovskii variable range hoping model. [ABSTRACT FROM AUTHOR]

Abstract: The present work reports the preparation and room temperature Raman study of polycrystalline magnetoelectric BiFeO3 (BFO) material. All the 13 Raman modes predicted by group theory (Γ Raman,R3c=4A 1+9E) for R3c structure of BFO are observed in the present work. To distinguish A 1 and E modes, Raman measurements have been carried out in parallel and crossed polarization configurations. In addition to other modes, intense sharp peaks corresponding to A 1-1, A 1-2, and A 1-3 modes at 135.15±1.38, 167.08±0.34 and 218.11±0.45cm−1, respectively, are clearly observed in the polycrystalline BFO sample. The results of Raman spectra matches well with the recently reported single crystal and epitaxially grown thin film of BFO. Further, X-ray diffraction (XRD), differential scanning calorimetry (DSC), Mossbauer spectroscopy, vibrating sample magnetometer are used to characterize the sample. The XRD result shows BFO as a major phase along with about 1% impurity phase. Mossbauer spectrum show sextet at room temperature indicating the magnetic ordering. The observed isomer shift indicates the presence of Fe in trivalent oxidation state. DSC is used to find the Neel temperature (T N). The observed hyperfine parameters and T N match well with the literature. The room temperature magnetization measurement indicates the anti-ferromagnetic nature of the BFO sample. [Copyright &y& Elsevier]

Abstract: In the present study, 57FePt films are prepared with reactive ion beam sputtering using mixture of argon and nitrogen gases. Energy-dispersive X-ray reflectivity is used to estimate the thickness of the as-deposited films. Structural and magnetic properties of the as-deposited and annealed films are studied using grazing incidence X-ray diffraction (GIXRD), magneto-optical Kerr effect (MOKE) and conversion electron Mossbauer spectroscopy (CEMS). Significant difference in structural and magnetic properties i.e., formation of ordered L10 phase and perpendicular magnetic anisotropy are observed for the films prepared with mixture of nitrogen and argon as compared to the film prepared with argon only. From the GIXRD, peaks corresponding to the ordered face-centred tetragonal FePt phase are observed for the films prepared with mixture gas. The results of CEMS clearly show the perpendicular magnetic anisotropy (PMA) for the films prepared with mixture of nitrogen and argon. The observed enhanced chemical ordering and the development of PMA in the films prepared with mixture gas is due to the role played by the defects created as a consequence of nitrogen escape in the films with high temperature annealing. [Copyright &y& Elsevier]