Paramagnetic Doublet Research Articles

Study of interparticle interaction in conjugates of magnetic nanoparticles injected into mice

In this work the first fast stage of the biodegradation in vivo of magnetic ferrofluid was investigated. The appearance of a paramagnetic doublet was observed in Mossbauer spectra of mouse liver within 2 h after intravenous injection of the ferrofluid. It was shown that nanosized superparamagnetic particles were combined into groups in the initial magnetic beads of the ferrofluid and were connected inside each group by magnetic dipole interaction. It was found that the appearance of a paramagnetic doublet in the spectrum of mouse liver is caused by the decrease of the magneto-dipole interaction between the superparamagnetic nanoparticles.

Magnetic and Mössbauer studies of Fe and Co co-doped SnO2

1–5% Fe and 1% Co co-doped SnO2 samples were synthesized by sol-gel method. Their magnetization increased with increasing crystal size of rutile SnO2. Their Mossbauer spectra contain a broad sextet, magnetic relaxation components, and paramagnetic doublet peaks for less than 3% Fe doping. The sextet of α-Fe2O3 was observed instead of magnetic relaxation peaks for Fe doping of above 4%. The broad sextet and relaxation components may be related to the magnetic properties of Fe and Co co-doped SnO2.

STRUCTURAL, ELECTRONIC STRUCTURE, TRANSPORT AND MAGNETIC STUDIES OF NdFe1-xNixO3(x = 0.4, 0.5)

The structural, transport, electronic structure and magnetic properties of NdFe 1-x Ni x O 3(x = 0.4, 0.5) samples are studied. Both the samples are in single phase with orthorhombic Pbnm structure. The transport properties show the semiconducting nature of the system and no transition is seen on the application of magnetic field. The electronic structure studies verify the chemical states of the ions in the embedded system and the symmetry of the interacting ions. The magnetic properties show the transition from ferromagnetic to paramagnetic phase and which is studied through the Mossbauer studies. The paramagnetic doublet in the x = 0.5 system clearly shows the phase transition from ferromagnetic to paramagnetic.

Reclassification of CK chondrites confirmed by elemental analysis and Fe-Mössbauer spectroscopy

Twenty CK chondrites collected in the Antarctica Continent were characterized by inductively-coupled plasma mass spectrometry (ICP-MS), prompt gamma ray analysis (PGA), instrumental neutron activation analysis (INAA), X-ray diffractometry (XRD) and 57Fe-Mossbauer spectroscopy. As a result of elemental analysis, it was revealed that 18.2~26.4 mass% of iron was included in the each chondrite. Mossbauer spectrum of LEW86258, classified as a typical CK chondrite, was found to be composed of two paramagnetic doublets and two magnetic sextets. Mossbauer spectra were assigned to the absorption due to forsterite (Mg1.36Fe0.64SiO4) and magnetite (Fe3O4), as also confirmed by XRD. XRD study of LAP03834, reclassified from CK to R chondrite, revealed the presence of crystalline phase due to forsterite. These results indicate that LAP03834 and related chondrites, i.e., MET01149, LAP03923 and MAC02453, should be reclassified as R or LL chondrite.

Mössbauer study of the Ordinary-Chondrite meteorite Thylacine Hole–001

The Thylacine Hole–001 meteorite was recovered from the Nullarbor Desert (Australia) in 1977 and is an Ordinary Chondrite, Group H4/5br, which has undergone moderate to severe (B/C) weathering. We have characterised the Fe-bearing phases in Thylacine Hole–001 by 57Fe Mossbauer Spectroscopy at 300 K, 100 K, 50 K and 4 K. The spectrum at 300 K is dominated by the paramagnetic doublets of Olivine, Pyroxene and a Ferric component which is most likely nanoparticulate Goethite. Magnetically split sextets due to Maghemite or Magnetite are also present, consistent with the relatively advanced terrrestrial age of 28,500 yrs The nanoparticulate Goethite component shows a blocked, magnetically split sextet at low temperatures. We also observe the effects of magnetic ordering of the Olivine and Pyroxene below 50 K.

Formation and superparamagnetic behaviors of LaFeO3 nanoparticles

Formation of LaFeO3 nanoparticles obtained from thermal decomposition of organometallic precursors was investigated as a function of the heat-treatment temperature. The precursors heat-treated below 300°C were amorphous, but above 350°C a single-phase of nanocrystalline LaFeO3 was formed. The LaFeO3 nanoparticles showed the superparamagnetic behavior in both magnetization and Mossbauer measurements. With increasing heat-treatment temperature, the crystallite size of LaFeO3 nanoparticles was gradually increased. The quadrupole splitting and isomer shift of paramagnetic doublet pattern were affected by the growth of LaFeO3 particles.

Magnetic properties of Fe and Co codoped SnO2 prepared by sol-gel method

SnO2 codoped with Fe and Co was prepared using the sol-gel method. Compared with SnO2 doped with only Fe or Co, the ferromagnetic saturation magnetization of the codoped SnO2 was enhanced because of the lattice distortion induced by codoping. Mössbauer spectra consist of two paramagnetic doublets and one broad sextet of high-spin Fe(III) species. The Mössbauer spectra revealed that the magnetic sextet with broad peaks is drastically modulated by doping with 0.5%–3% Co and 1% Fe codoped SnO2. Our experimental results suggest correlation between the enhancement of the saturation magnetization and the appearance of sextet peaks.

Characterization of the Carancas–Puno meteorite by energy dispersive X-ray fluorescence, X-ray diffractometry and transmission Mössbauer spectroscopy

We report the results of the study of a meteorite that impacted an inhabited zone on 15 September 2007 in the neighborhood of the town of Carancas, Puno Region, about 1,300 km south of Lima. The analysis carried out by energy dispersive X-ray fluorescence, X-ray diffractometry and transmission Mossbauer spectroscopy (at room temperature and at 4.2 K), reveal the presence in the meteorite sample of magnetic sites assigned to taenite (Fe,Ni) and troilite (Fe,S) phases, and of two paramagnetic doublets assigned to Fe2 + , one associated with olivine and the other to pyroxene. In accord with these results, this meteorite is classified as a type IV chondrite meteorite.

Physico-chemical investigation on mixed alkali metal ferrites prepared by solution combustion method – A comparative study

Mixed alkali metal nanoferrites of the compositions M 0.5− X /2 Zn X Mn 0.05 Fe 2.45− X /2 O 4 (M = Li, Na and K), where x varies from 0→0.5 in steps of 0.1, have been prepared by solution combustion method. Powder X-ray diffraction analysis for all the samples show the formation of single phase cubic spinel structure. The lattice parameter increases linearly with Zn content, which is attributed to ionic size differences of the cations involved. Both X-ray as well as experimental densities show upward trend with increasing ‘ x ’ due to increase in the molecular weight of the ferrite composition. Mössbauer spectra display the superimposition of paramagnetic doublet over ferrimagnetic sextet with increasing diamagnetic ‘Zn’ content. The key magnetic properties of the ferrite obtained, such as saturation magnetization and Curie temperature have also been studied. The combustion method used for the synthesis is a rapid approach for direct conversion of the stoichiometric reactant solutions into fine nanoparticles of ferrite product at a temperature (600 °C) much lower than that of the conventional ceramic method. Scanning electron micrographs confirm the formation of nanosized ferrites.

Mössbauer Spectroscopic Analysis of Nd<sub>2</sub>Fe<sub>14</sub>B/α-Fe Hard Magnetic Nanocomposites

Among novel magnetic intermetallics based on rare earth-transition compounds, the Nd2Fe14B/α-Fe isotropic nanocomposites have been obtained by recrystallization from an amorphous phase, prepared by melt spinning. For variable 5 wt.% Fe and 10 wt.% Fe contents we recorded transmission 57Fe Mössbauer spectra at the room temperature, hardened of the α-Fe phase by exchange interactions. The spectra have been analyzed in terms of ten Zeeman sextets and one paramagnetic doublet related to the Nd1.1Fe4B4 phase. One sextet corresponds to the α-Fe phase, whereas others are attributed to six non-equivalent Fe sites in the Nd2Fe14B structure, namely 16k1, 16k2, 8j1, 8j2, 4c, and 4e. The three remaining sextets belong to the Fe3B structure with three inequivalent Fe sites FeI(8g), FeII(8g) and FeIII(8g). All relevant parameters for both nanocomposites: the magnetic hyperfine field, the isomer shift and the quadrupole splitting are determined for each of these sites.

Mössbauer spectra of MnFe2−2x Al2x O4 (0≼x≼0.4) ferrites

The effect of non-magnetic Al3+ ion doping on the magnetic properties of MnFe2−2x Al2x O4 (0≼x≼0.4) spinel ferrites was studied using Mossbauer spectroscopy measurements at room temperature. From the Mossbauer study, it is observed that the resolved hyperfine sextets are due to the distribution of Fe ions on the two sublattices of the spinel ferrites. The value of the isomer shift obtained from the fitting of the Mossbauer spectra indicates that Fe ions are in +3 state. A paramagnetic doublet is observed at degree of inversion x=0.4, superimposed on the hyperfine sextets, indicating that the super-exchange interaction A–B decreases due to the dilution of sublattice by Al3+ ions. The hyperfine magnetic field decreases at both interstitial sites of tetrahedral (A) and octahedral (B) with the increase in Al concentration.

Nano particles of iron oxides in SiO2 glass prepared by ion implantation

Quartz (SiO2) glass was implanted with 5 × 1016 57Fe ions/cm2 at a substrate temperature of 500 °C, and annealed at temperatures between 700 and 950 °C. The implanted and annealed plates were characterized by conversion electron Mossbauer spectroscopy (CEMS), and measured by a Kerr effect magnetometer or a vibration sample magnetometer. Kerr effect measurement of as-implanted SiO2 glass showed ferromagnetism at room temperature. CEM spectrum of the as-implanted glass consisted of magnetic relaxation peaks of finely dispersed metallic Fe species, and paramagnetic doublets of Fe3+ and Fe2+ species. The sample heated at 700 °C contained large grains of metallic Fe and a lot of oxidation products of Fe2+ species. After oxidation at temperatures higher than 800 °C, the samples showed also ferromagnetism, which was attributed mainly to ferromagnetic e-Fe2O3 precipitated in SiO2 matrix. Small amounts of α-Fe2O3 were produced at 950 °C. The results suggest that ion implantation and oxidation make a transparent ferromagnetic glass possible.

SYNTHETIC CUBANITE CuFe2S3: PRESSURE-INDUCED TRANSFORMATION TO ISOCUBANITE

Cubanite, the orthorhombic polymorph of CuFe 2 S 3 , is very sensitive to temperature, pressure and compositional variations. This sensitivity has prevented its successful synthesis in a controlled laboratory environment. We report here the first successful synthesis of cubanite and its high-pressure Mossbauer spectroscopic and electrical properties up to 7 GPa. We also compare the Mossbauer spectroscopic and electrical resistivity results on our synthetic cubanite with the behavior of naturally occurring cubanite under identical conditions. The magnetic hyperfine field, a sensitive Mossbauer parameter of the synthetic sample, corresponds to that of orthorhombic cubanite. We report here the pressure-induced transformation of the magnetic sextet (cubanite) to a paramagnetic doublet (isocubanite) at ~4 GPa at room temperature. This transformation has been confirmed independently by our electrical resistivity measurements up to 7 GPa. The present results could be useful in estimating the metamorphic pressure conditions of cubanite-bearing carbonaceous chondrites.

ChemInform Abstract: Local Structure, Tg, and IR Transparency of Potassium Titanate Glasses and the Local Structure of Calcium Titanate Ceramics.

The Mossbauer spectrum of xK2O·(95−x)TiO2·5Fe2O3 glasses (x=35–60), consisting of a paramagnetic doublet peak due to tetrahedral Fe3+, suggests that the Fe3+ is substituted for the tetrahedral Ti4+. The isomer shift (δ=0.20–0.23 mm s−1) and the quadrupole splitting (Δ=0.72–0.81 mm s−1) decrease linearly with the increasing K2O content. The glass transition temperature (Tg) decreases similarly as the Δ does, supporting the “Tg−Δ rule” discovered by Nishida et al., i.e., the Tg of oxide glasses is expressed by Tg=aΔ+b. (The slope “a” is 680 °C mm−1 s.) The IR absorption spectra show two peaks at 880 and 640 cm−1 corresponding to the Ti(Fe)O4 and TiO6 units, respectively. The relative absorption intensity of the Ti(Fe)O4 units becomes higher when the K2O content increases. The potassium titanate glasses (plate) show IR transparency, having the transmission edge of 5.4 μm. The Mossbauer spectrum of xCaO·(95−x)TiO2·5Fe2O3 ceramics (x=5–50) consists of two doublet peaks due to Fe3+ and Fe2+. Both the δ and Δ of...

Mechanical strength and local structure of 'new' Hagi porcelain investigated by 57Fe-Mössbauer spectroscopy

A relationship between the local structure and mechanical strength of 'new' Hagi porcelain 'A' and 'B' prepared by sintering two types of iron containing aluminosilicate soils under oxidizing and reducing atmospheres were investigated by means of 57Fe-Mössbauer spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), as well as three point bending test. The largest mechanical strength (σ) value of 64.3±3.1 MPa was estimated from the three-point bending test of reductively sintered Hagi porcelain 'A'. The Mössbauer spectrum was composed of two paramagnetic doublets due to tetrahedral FeII FeIII with the isomer shift (δ) values of 1.13±0.02 and 0.31±0.01 mm s−1. On the other hand, a paramagnetic doublet and a magnetic sextet with the δ values of 0.30±0.01 and 0.35±0.02 mm s−1 were observed from the Mössbauer spectra of other samples. It can be concluded that the mechanically strengthened Hagi porcelain was successfully fabricated by choosing soil 'A' and by sintering under a reducing atmosphere.

Controlled propulsion in viscous fluids of magnetically actuated colloidal doublets

We study the propulsion of a micron-size paramagnetic colloidal doublet dispersed in water and driven above a surface by an external precessing magnetic field. The applied field forces the doublet to precess around an axis parallel to the plane of motion and the rotation of the colloidal assembly is rectified into translation due to a periodic asymmetry in dissipation close to the bounding plate. These recent experimental findings [P. Tierno, R. Golestanian, I. Pagonabarraga, and F. Sagués, Phys. Rev. Lett. 101, 218304 (2008)] are complemented here with a theoretical analysis of the system and extended to more complex magnetic modulations such as elliptical driving fields. Experimental results show a good agreement with numerical simulations with the aim to find the best conditions toward the optimization of propulsion speed and swimming efficiency.

Characterization of nanosized spinel ferrite powders synthesized by coprecipitation and autocombustion method

Abstract Magnetic nanoparticles of magnetite (Fe3O4) and NiCuZn-doped magnetite (Ni0.35Cu0.15Zn0.5Fe2O4) were prepared by coprecipitation and by sol–gel combustion methods accordingly. The average size, d, of magnetite nanoparticles (d = 12 nm) and the NiCuZn ferrite nanoparticles ignited at about 250 °C (d = 30 nm) was estimated from X-ray diffraction patterns. The Mossbauer spectroscopy revealed the existence of the paramagnetic doublet in both samples. For magnetite, coercive force of about 400 Oe was found at 5 K. Likewise, the coercive field of the NiCuZn-doped magnetite nanoparticles decreases with Fe2+ substitution at low temperature (260 Oe). This behavior can be explained taking into account the fact that the magnetocrystalline anisotropy constant of Fe3O4 is higher than that of NiCuZn ferrite.

High efficiency of natural lamellar remanent magnetisation in single grains of ilmeno-hematite calculated using Mössbauer spectroscopy

Rocks from large remanent magnetic anomalies on Earth have been found to contain exsolved rhombohedral oxides, which also have been proposed as earth analogues for the rocks creating the observed large remanent anomalies on Mars. Theoretical considerations and previous case studies of natural rocks have shown that the natural magnetisation is carried by lamellar magnetism due to uncompensated moments at the interface between antiferromagnetic hematite and paramagnetic ilmenite. Here, single grains (≈ 250 µm) of titanohematite with ferri-ilmenite exsolution lamellae from Mesoproterozoic metamorphic rock samples in southwest Sweden and the Adirondack Mountains, USA, are studied using room-temperature Mossbauer spectroscopy to identify possible characteristic magnetic signatures of lamellar magnetism. Mossbauer spectra of synthetic samples of titanohematite (Fe0.95Ti0.05O3 and Fe0.9Ti0.1O3) were collected for comparison and showed a dominant six-line magnetic spectrum due to Fe3+ in titanohematite with a weak sextet due to Fe2+–Fe3+ charge transfer. Mossbauer spectra of the natural ilmeno-hematite grains are similar to those for synthetic titanohematite, but contain additionally two paramagnetic doublets corresponding to Fe2+ and Fe3+ in ilmenite. However, several grains also contain an additional weak, broad magnetic component that we assign to iron in contact layers according to the lamellar magnetism model. Similar to the previous Mossbauer results for natural hemo-ilmenite, there is no evidence for superparamagnetic behaviour of the nanoscale titanohematite lamellae contained within coarser ferri-ilmenite lamellae, and no evidence for single-domain or superparamagnetic magnetite. The compositions of titanohematite and ferri-ilmenite in the individual ilmeno-hematite grains calculated from the Mossbauer area ratios show that compositions are closer to end-member values than the compositions inferred from electron microprobe and transmission electron microscopy on the same grains, consistent with observations that lamella thicknesses are as small as a few nm. Bulk compositions of ilmeno-hematite grains calculated from the Mossbauer data confirm that the Swedish samples are significantly more ilmenite-rich than the Adirondack samples, and agree with an estimation of bulk composition through point counting of electron backscatter images. The Mossbauer data allow a quantitative estimation of contact layer abundance, which is used to determine the efficiency of lamellar natural remanent magnetisation acquisition. Because minerals with a high natural remanent magnetisation efficiency are expected to create larger remanent magnetic anomalies, contact layer abundance determination by Mossbauer spectroscopy provides a valuable new tool for mineral-based magnetic anomaly interpretation on Earth and other planetary bodies.

Structural and magnetic properties of Fe–Ni mecanosynthesized alloys

Fe100 − xNix samples with x = 22.5, 30.0 and 40.0 at.% Ni were prepared by mechanical alloying (MA) with milling times of 10, 24, 48 and 72 h, a ball mass to powder mass (BM/PM) ratio of 20:1 and rotation velocity of 280 rev/min. Then the samples were sintered at 1,000°C and characterized by X-ray diffraction (XRD) and transmission Mossbauer spectrometry (TMS). From the refinement of the X ray patterns we found in this composition range two crystalline phases, one body centered cubic (BCC), one face centered cubic (FCC) and some samples show FeO and Fe3O4 phases. The obtained grain size of the samples shows their nanostructured character. Mossbauer spectra were fitted using a model with two hyperfine magnetic field distributions (HMFDs), and a narrow singlet. One hyperfine field distribution corresponds to the ferromagnetic BCC grains, the other to the ferromagnetic FCC grains (Taenite), and the narrow singlet to the paramagnetic FCC grains (antitaenite). Some samples shows a paramagnetic doublet which corresponds to FeO and two sextets corresponding to the ferrimagnetic Fe3O4 phase. In this fit model we used a texture correction in order to take into account the interaction between the particles with flake shape and the Mossbauer \(\upgamma\)-rays.

Ferromagnetic and antiferromagnetic behaviour in Ba(Fe0.5Ta0.5)O3 ceramics

Ba(Fe0.5Ta0.5)O3 ceramics with a cubic crystal structure in space group (2 2 1) were prepared by a solid-state reaction process, and the magnetic characteristics were evaluated systematically. Ba(Fe0.5Ta0.5)O3 was antiferromagnetic with a slight ferromagnetic moment below 20 K, and above this temperature a weak ferromagnetic nature was revealed. To clarify the origin of the magnetic behaviour, the crystal structure and the magnetic characteristics of Al-substituted Ba(Fe0.5Ta0.5)O3 ceramics were investigated, and the weakened ferromagnetic ordering was revealed compared with the pure Ba(Fe0.5Ta0.5)O3 ceramics. The 57Fe Mössbauer spectra at room temperature showed that iron was the centre paramagnetic doublet in both pure Ba(Fe0.5Ta0.5)O3 and Al-substituted Ba(Fe0.5Ta0.5)O3 ceramics, and the reduction in Fe2+ was detected in Al-substituted Ba(Fe0.5Ta0.5)O3 ceramics. These analytical results suggested that oxygen vacancies appeared to play an important role in the room temperature ferromagnetism in Ba(Fe0.5Ta0.5)O3 ceramics. Although the antiferromagnetism has been reported previously, the weak ferromagnetic nature at room temperature had never been observed before.