Magnetic and Mössbauer spectroscopic studies of NiZn ferrite nanoparticles synthesized by a combustion method

The properties of nanocrystalline Ni_0.5Zn_0.5Fe₂O₄ synthesized by an auto-combustion method have been investigated by magnetic measurements and Mössbauer spectroscopy. The as-synthesized single phase nanosized ferrite powder is annealed at different temperatures in the range 673–1,273 K to obtain nanoparticles of different sizes. The powders are characterized by powder X-ray diffraction, vibrating sample magnetometer, transmission electron microscopy and Mössbauer spectroscopy. The as-synthesized powder with average particle size of ~9 nm is superparamagnetic. Magnetic transition temperature increases up to 665 K for the nanosized powder as compared to the transition temperature of 548 K for the bulk ferrite. This has been confirmed as due to the abnormal cation distribution, as evidenced from room temperature Mössbauer spectroscopic studies.     

Mössbauer study of a Fe3O4/PMMA nanocomposite synthesized by sonochemistry

Magnetite nanoparticles of 10 nm average size were synthesized by ultrasonic waves from the chemical reaction and precipitation of ferrous and ferric iron chloride (FeCl₃ · 6H₂O y FeCl₂ · 4H₂O) in a basic medium. The formation and the incorporation of the magnetite in PMMA were followed by XRD and Mössbauer Spectroscopy. These magnetite nanoparticles were subsequently incorporated into the polymer by ultrasonic waves in order to obtain the final sample of 5 % weight Fe₃O₄ into the polymethylmethacrylate (PMMA). Both samples Fe₃O₄ nanoparticles and 5 % Fe₃O₄/PMMA nanocomposite, were studied by Mössbauer spectroscopy in the temperature range of 300 K–77 K. In the case of room temperature, the Mössbauer spectrum of the Fe₃O₄ nanoparticles sample was fitted with two magnetic histograms, one corresponding to the tetrahedral sites (Fe^3?+?) and the other to the octahedral sites (Fe^3?+? and Fe^2?+?), while the 5 % Fe₃O₄/PMMA sample was fitted with two histograms as before and a singlet subspectrum related to a superparamagnetic behavior, caused by the dispersion of the nanoparticles into the polymer. The 77 K Mössabuer spectra for both samples were fitted with five magnetic subspectra similar to the bulk magnetite and for the 5 % Fe₃O₄/PMMA sample it was needed to add also a superparamagnetic singlet. Additionally, a study of the Verwey transition has been done and it was observed a different behavior compared with that of bulk magnetite.     

Study of NiFe2O4 nanoparticles using Mössbauer spectroscopy with a high velocity resolution

The nanocrystalline NiFe₂O₄ particles prepared by solution combustion synthesis technique using different fuels such as ethylene-diamine-tetra-acetic acid (NA sample) and urea (NB sample) were studied using magnetic measurement and ⁵⁷Fe Mössbauer spectroscopy with a high velocity resolution. The temperature dependence of magnetization is different for the two samples. Mössbauer spectra demonstrate the necessity to use more than two magnetic sextets, usually used to fit the NiFe₂O₄ nanoparticles spectra. Evaluation of the different local microenvironments for Fe in both tetrahedral (A) and octahedral (B) sites, caused by different Ni^2?+? occupation of octahedral sites, demonstrates at least five different local microenvironments for both A and B sites. Therefore, the Mössbauer spectra were fitted by using ten magnetic sextets which are related to the spread ⁵⁷Fe location in octahedral and tetrahedral sites.     

Mössbauer Studies of Nanosize CuFe2O4 Particles

⁵⁷Fe Mössbauer spectra of pulsed-laser deposited (PLD) films of CoFe₂O₄ of 0.3 µm thickness is investigated using transmission geometry is reported. Mössbauer parameters were determined for the tetrahedral (A) and octahedral (B) sites. The PLD processed films gave measurable spectra with no visible evidence of clustering or multiple phases present. Results on the films agreed with those of the bulk material. The films exhibited magnetic hyperfine and quadruple splittings similar to that of bulk CoFe₂O₄. This work demonstrates that measurable transmission Mössbauer spectra may be obtained for PLD deposited CoFe₂O₄ thick films.     

X-ray diffraction and Mössbauer spectroscopy of high energy ball-milled α-Fe2O3/TiO2 composite powders

α–Fe₂O₃/TiO₂ Composite powders have been prepared by high energy ball-milling for different times. The composites were studied using Mössbauer Spectroscopy (MS) and X-ray diffraction (XRD). The patterns of XRD show broadening in the diffraction peaks, indicating a decrease in the particle size of the composites with milling time. Also, the XRD patterns show an evolving new structural phase correlated with an evolving Titanium ferrite species with milling time. Mössbauer Spectroscopy shows the evolving titanium ferrite species characterized by a quadrupole doublet at the expense of the α–Fe₂O₃ represented by the magnetic sextet. The doublet corresponding to the Ti-ferrite phase dominates the Mössbauer spectra at long milling time (greater than 100 h of milling).     

Magnetic and Mössbauer studies of fucan-coated magnetite nanoparticles for application on antitumoral activity

Fucan-coated magnetite (Fe₃O₄) nanoparticles were synthesized by the co-precipitation method and studied by Mössbauer spectroscopy and magnetic measurements. The sizes of the nanoparticles were 8–9 nm. Magnetization measurements and Mössbauer spectroscopy at 300 K revealed superparamagnetic behavior. The magnetic moment of the Fe₃O₄ is partly screened by the Fucan coating aggregation. When the magnetite nanoparticles are capped with oleic acid or fucan, reduced particle-particle interaction is observed by Mössbauer and TEM studies. The antitumoral activity of the fucan-coated nanoparticles were tested in Sarcoma 180, showing an effective reduction of the tumor size.     

Mössbauer studies on Al−Co ferrites

Mössbauer spectroscopy studies have been performed on the spinel CoAl_xFe_2?xO₄ (2<-x<-1.7) in the temperature range 77–750 K using either a liquid nitrogen bath cryostat or a furnace. The samples are magnetic at 77 K giving spectra that have magnetic sextets coexisting with a central line which increases in population with the Al-content indicating relaxation effects. The data shows that Al possesses no preference to either tetrahedral or octahedral sites of the ferrite over the whole range of concentration. The Mössbauer hyperfine interaction parameters and magnetic transition temperatures were determined. As expected the hyperfine field and Curie temperature decrease when the Al-content increases.     

Mössbauer spectra of iron-chromium sulphospinels with varying metal ratio

Samples of the sulphospinel FeCr₂S₄ with varying Fe/Cr ratio around the nominal composition have been investigated with Mössbauer spectroscopy. The spectra with the narrowest lines, as well as a γ-type peak in the specific heat-temperature curve at the low temperature transition previously described, were obtained for an overall composition with a small Fe deficit. The broadening often observed in Mössbauer spectra of FeCr₂S₄ samples is attributed to Fe²⁺ on octahedral sites in the spinel phase, resulting in an electric field gradient at the Fe²⁺ ions on the tetrahedral sites. The paramagnetic Mössbauer spectrum of Fe_1.06Cr_1.94S₄ is in accordance with this interpretation.     

Thermal decomposition of almandine garnet: Mössbauer study

The thermal decomposition of almandine garnet from Zoltye Vody, Ukraine, has been studied using⁵⁷Fe Mössbauer spectroscopy. Room temperature Mössbauer spectrum of the initial powdered sample is characterised by one doublet corresponding to Fe²⁺ in dodecahedral position 24c. In the room temperature spectra of all heated almandine samples, a doublet corresponding to γ-Fe₂O₃ nanoparticles appeared. Depending on experimental conditions (heating temperature and time), the additional spectral lines of α-Fe₂O₃ and ε-Fe₂O₃ were observed in Mössbauer spectra. It is obvious that the thermal transformation of almandine garnet in air is related to the primary formation of γ-Fe₂O₃ superparamagnetic nanoparticles. γ-Fe₂O₃ nanoparticles are transformed into ε-Fe₂O₃ and consequently into α-Fe₂O₃ at higher temperatures. The mechanism and kinetics of the individual structural transformations depend on experimental conditions — mainly on the heating temperature and size of the particles.     

Magnetic properties and local configurations of <Superscript>57</Superscript>Fe atoms in CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> powders and CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/PVA nanocomposites

The composition and magnetic properties of the powders extracted from CoFe₂O₄ aqueous suspensions and the CoFe₂O₄/PVA (PVA is polyvinyl alcohol) nanocomposites with a cobalt ferrite content of 10–30 wt % have been investigated using Mössbauer spectroscopy, transmission electron microscopy, and vibration magnetometry. The cationic formulas of the cobalt ferrites synthesized have been determined. The differences between samples synthesized at temperatures of 72.5 and 82.5°C have been revealed. The specific features of the observed changes in the agglomeration of CoFe₂O₄ particles after introducing into the PVA matrix have been studied. It has been shown that the iron ion distribution determined by Mössbauer spectroscopy in octahedral and tetrahedral lattice sites correlates with vibration magnetometry data.     

Mössbauer studies and magnetic properties of spinel lead ferrite

In the present communication, we have reported the synthesis of nanocrystalline lead ferrite (PbFe₂O₄) by citrate mediated autocombustion method. X-ray diffraction pattern reveals the single phase formation in cubic (spinel) structure. The particle size and the surface morphology of the samples are characterized by TEM and SEM analysis. Magnetic studies are carried out using vibrating sample magnetometer (VSM) shows a very high coercive field for the material. Mössbauer studies were performed to investigate the local symmetry i.e. Fe is in octahedral/tetrahedral site and the charge states of Fe ions.     

Study of CuFe2O4–SnO2 nanocomposites by Mössbauer spectroscopy with high velocity resolution

High velocity resolution Mössbauer spectroscopy was used to study of (CuFe₂O₄)_1???x (SnO₂) _x nanocomposites (x?= 0, 1, 5, 10, 20 wt.%). Mössbauer spectra were measured at room temperature with registration in 4,096 channels and further presentation in 1,024 channels. Mössbauer spectra of CuFe₂O₄ and (CuFe₂O₄)_0.99 + (SnO₂)_0.01 were better fitted using three sextets while spectra of (CuFe₂O₄)_0.95 + (SnO₂)_0.05 and (CuFe₂O₄)_0.80 + (SnO₂)_0.20 were better fitted using four sextets and one doublet. In contrast, spectrum of (CuFe₂O₄)_0.80 + (SnO₂)_0.20 was better fitted using five sextets and one doublet. Mössbauer hyperfine parameters were related to octahedral and tetrahedral sites in copper ferrites. The presence of two different tetrahedral sites in studied ferrites and two different octahedral sites in (CuFe₂O₄)_0.80 + (SnO₂)_0.20 was supposed.     

Hyperfine field and relaxation effect in Li−Zn−Ti ferrites

⁵⁷Fe Mössbauer effect studies were made on titanium substituted Li?Zn ferrite with composition Li_0.45+0.5tZn_0.1 Ti_t Fe_2.45–1.5tO₄ (t=0.0 to 1.2) at 300K. The Mössbauer spectra for t≤0.4 show two well defined Zeeman sextets corresponding to the Fe³⁺ ions at tetrahedral (A) and octahedral (B) sites. The spectra for t=0.6, 0.8 and 0.9 show relaxation but can still be resolved into 2 sextets. The spectra for t=1.0, 1.2 show strong ferrimagnetic relaxation with the spectra for t=1.2 exhibiting an additional central doublet. The effect of Ti⁴⁺ substitution on the Isomer shift (I.S), Quadrupole splitting (Q.S.) and nuclear magnetic fields of Li?Zn ferrites have been reported in this paper. The I.S. was found to be independent of substitution level t, while the quadrupole splitting was observed to be negligible. The variation of hyperfine field with t has been explained on the basis of superexchange interaction and cation distribution.     

Synthesis and characterization of uncoated and gold-coated magnetite nanoparticles

We report on the synthesis and characterization of uncoated and gold coated magnetite nanoparticles. Structural characterizations, carried out using X-ray diffraction, confirm the formation of magnetite phase with a mean size of ~7 and ~8 nm for the uncoated and gold covered magnetite nanoparticles, respectively. The value of the gold coated Fe₃O₄ nanoparticles is consistent with the mean physical size determined from transmission electron microscopy images. Mössbauer spectra at room temperature are consistent with the thermal relaxation of magnetic moments mediated by particle-particle interactions. The 77 K Mössbauer spectra are modeled with four sextets. Those sextets are assigned to the signal of iron ions occupying the tetrahedral and octahedral sites in the core and shell parts of the particle. The room-temperature saturation magnetization value determined for the uncoated Fe₃O₄ nanoparticles is roughly ~60 emu/g and suggests the occurrence of surface effects such as magnetic disorder or the partial surface oxidation. These surface effects are reduced in the gold-coated Fe₃O₄ nanoparticles. Zero-field–cooled and field-cooled curves of both samples show irreversibilities which are consistent with a superparamagnetic behavior of interacting nanoparticles.     

Application of 57Fe Mössbauer spectroscopy as a tool for mining exploration of bornite (Cu5FeS4) copper ore

Nuclear resonance methods, including Mössbauer spectroscopy,are considered as unique techniques suitable for remote on-line mineralogical analysis. The employment of these methods provides potentially significant commercial benefits for mining industry. As applied to copper sulfide ores, Mössbauer spectroscopy method is suitable for the analysis noted. Bornite (formally Cu₅FeS₄) is a significant part of copper ore and identification of its properties is important for economic exploitation of commercial copper ore deposits. A series of natural bornite samples was studied by ⁵⁷Fe Mössbauer spectroscopy. Two aspects were considered: reexamination of ⁵⁷Fe Mössbauer properties of natural bornite samples and their stability irrespective of origin and potential use of miniaturized Mössbauer spectrometers MIMOS II for in-situ bornite identification. The results obtained show a number of potential benefits of introducing the available portative Mössbauer equipment into the mining industry for express mineralogical analysis. In addition, results of some preliminary ^63,65Cu nuclear quadrupole resonance (NQR) studies of bornite are reported and their merits with Mössbauer techniques for bornite detection discussed.     

Magnetic Study of Nanocrystalline Ferrites and the Effect of Swift Heavy Ion Irradiation

100 MeV Si⁺⁷ irradiation induced modifications in the structural and magnetic properties of Mg_0.95Mn_0.05Fe₂O₄ nanoparticles have been studied by using X-ray diffraction, Mössbauer spectroscopy and a SQUID magnetometer. The X-ray diffraction patterns indicate the presence of single-phase cubic spinel structure of the samples. The particle size was estimated from the broadened (311) X-ray diffraction peak using the well-known Scherrer equation. The milling process reduced the average particle size to the nanometer range. After irradiation a slight increase in the particle size was observed. With the room temperature Mössbauer spectroscopy, superparamagnetic relaxation effects were observed in the pristine as well as in the irradiated samples. No appreciable changes were observed in the room temperature Mössbauer spectra after ion irradiation. Mössbauer spectroscopy performed on a 12 h milled pristine sample (6 nm) confirmed the transition to a magnetically ordered state for temperatures less than 140 K. All the samples showed well-defined magnetic ordering at 5 K, whereas, at room temperature they were in a superparamagnetic state. From the magnetization studies performed on the irradiated samples, it was concluded that the saturation magnetization was enhanced. This was explained on the basis of SHI irradiation induced modifications in surface states of the nanoparticles.     

Mechanosynthesis of spinel ferrite nanoparticles followed by Mössbauer spectroscopy

The single-step synthesis of nanosized MgFe₂O₄ and NiFe₂O₄ via mechanochemical processing of binary oxide precursors is followed by ⁵⁷Fe Mössbauer spectroscopy. Quantitative information is provided on both ionic and spin configurations in mechanosynthesized spinels. The response of the mechanosynthesized ferrite nanoparticles to changes in temperature is also studied.     

Magnetic properties of γ-Fe2O3 nanoparticles encapsulated in surface-treated polymer spheres

Mössbauer and magnetic characterization of polymer-dispersed γ-Fe₂O₃ nanoparticles treated under different chemical processes are reported in this work. X-ray powder diffraction analysis provides a mean particle size of D ~ 8.0 nm. Whereas Mössbauer spectroscopy data suggest the presence of only Fe^3?+? ions, magnetization measurements indicate the occurrence of a freezing phenomenon in agreement with the thermal evolution of Mössbauer spectra. A core–shell model was used to determine a magnetically disordered layer (shell) of d ~ 1.0 nm covering a region of collinear magnetic moments (core). The chemical treatments with H₂O₂ and Na₂S₂O₈ modify notoriously the magnetic response of the polymer-dispersed nanoparticles.     

Magnetic nanoparticles coated with polysaccharide polymers for potential biomedical applications

This study reports a two-steps route for obtaining magnetic nanoparticles–polysaccharide hybrid materials consisting of Fe₃O₄, NiFe₂O₄ and CuFe₂O₄ nanoparticles synthesis by coprecipitation method in the presence of a soft template followed by coating of ferrite nanoparticles of 8–10-nm size range with polysaccharide type polymers—sodium alginate or chitosan. Magnetic oxide nanoparticles and the corresponding hybrid materials were characterized by X-ray diffraction (XRD), Mössbauer spectroscopy, atomic absorption spectroscopy (AAS), FTIR spectroscopy, scanning and transmission electron microscopy (SEM and TEM) and specific surface area measurements. The vibrating sample magnetometry confirms the superparamagnetic properties of the synthesized ferrites and hybrids. Using this route, the percent of magnetic nanoparticles retained in chitosan-based hybrid materials is nearly double in comparison with that of sodium alginate–based materials. The biological activity tests on Escherichia coli ATCC 25922, Pseudomonas aeroginosa ATCC 27853, Staphylococcus aureus ATCC 25923 and Candida scotti microorganisms show the non-toxic properties of prepared hybrid materials.