Frequency-dependent Magnetic Susceptibility Research Articles

Cyanido-Bridged {LnIIIWV} Heterobinuclear Complexes: Synthesis and Magneto-Structural Study

A new series of cyanido-bridged {LnIIIWV} heterobinuclear complexes of formula [LnIII(pyim)2(i-PrOH)(H2O)2(μ-CN)WV(CN)7]·2H2O [Ln = Gd (1), Tb (2), Dy (3), Ho (4), and Er (5); pyim = 2-(1H-imidazol-2-yl)-pyridine) and i-PrOH = isopropyl alcohol] were synthesized by one-pot reaction between (NH3Bu)3[W(CN)8] and [Ln(pyim)2]2+ complexes (generated in situ by mixing the corresponding LnIII ions and the pyim ligand). Compounds 1-5 are isomorphous and crystallize in the monoclinic system P21/n space group. Their crystal structure consists of binuclear units in which the octacyanotungstate(V) anion coordinates to the corresponding LnIII ion through a single cyanide ligand. The tungsten(V) and lanthanide(III) ions are eight-coordinated, in distorted square antiprism (WV) and distorted trigonal dodecahedron (LnIII) geometries, respectively. The direct-current (dc) magnetic properties for 1-5 reveal the occurrence of weak antiferromagnetic interactions between WV and LnIII cation, with 8S7/2, 7F6, 6H15/2, 5I8, and 4I15/2 as ground terms for GdIII, TbIII, DyIII HoIII, and ErIII, respectively [JWLn = -1.19(1) (1), -1.02(2) (2), -1.10(2) (3), -1.30(2) (4), and -1.50(3) cm-1 (5), the spin Hamiltonian being defined as H = -JWLn SW·SLn]. The fit of the χMT data of 2-4 points out a positive value for the energy gap between the ML components (Δ). This feature is corroborated by their Q-band electron paramagnetic resonance spectra at low temperature, which clearly show MJ = 0 (2 and 4) and ±1/2 (3 and 5). Incipient frequency-dependent alternating-current magnetic susceptibility signals are observed for 3 and 5 under applied dc fields supporting the presence of slow magnetic relaxation behavior, the blocking temperatures being below 2.0 K. This new series of {LnIIIWV} heterobinuclear compounds provides more insights into the exchange magnetic interaction between 5d and 4f centers via the cyanide-bridge, for which scarce information is available to date.

Evaluation of the influence of cultivation period on soil redistribution in northeastern China using magnetic susceptibility

Magnetic susceptibility has been shown to be a reliable, economic and rapid method for tracking soil redistribution; however, more case studies are necessary to verify the link between soil movement and magnetic susceptibility. In this study, we sought to evaluate soil redistribution in northeastern China using magnetic susceptibility on the basis of data collected from croplands with different cultivation periods. The results showed that the magnetic susceptibility values, whether low-frequency magnetic susceptibility (χlf) or frequency-dependent magnetic susceptibility (χfd), were markedly different between forestland and cropland, with larger differences for longer cultivation periods. The magnetic susceptibility increased dramatically in topsoils on forest slope, whereas the difference in magnetic susceptibility between topsoils and subsoils decreased in cropland as the cultivation period increased. The magnetic susceptibility values varied significantly across sites on a given slope, increasing gradually from the upperslope to the lowerslope, regardless of whether the slope was forestland or cropland. Longer cultivation periods resulted in larger differences between the upperslopes and lowerslopes which were particularly notable when the cultivation period was longer than 50 years. For middleslopes and lowerslopes, the soil loss of an 110-year cultivated slope was approximately two times higher than that of a 30-year cultivated slope. These findings suggest that the use of magnetic susceptibility is feasible for tracking soil redistribution and soil loss.

The effect of interparticle interactions on spin glass and hyperthermia properties of Fe3O4 nanoparticles

Water dispersible Fe3O4 nanoparticles (NPs) were prepared, forming a durable suspension for several days. The zero field cooled magnetization peak temperature is ~4.5 times larger than the average blocking temperature, suggesting the presence of interparticle interactions. Frequency dependent AC magnetic susceptibility revealed superspin glass state at low temperatures. Also a signature of size dependent surface spin glass state was observed associated with a hump in in-phase and a peak in out-of phase susceptibility curves. Magnetic hyperthermia studies indicated that interparticle interactions influence the heat generation of NPs in an AC magnetic field. The temperature rise of 7 nm particles obtained was 8 times larger than that of 5 nm particles. This study shows the important role of interparticle interactions on magnetic and hyperthermia properties of magnetic NPs.

Magnetic properties of surface sediments as proxies of recent anthropogenic pollution in the Anllóns riverbed (NW Spain)

A study of surface sediments from the Anllons riverbed (northwestern Spain) was conducted to assess the use of their magnetic properties as proxies of recent trace element contamination (i.e., As, Zn, Pb, Cr, Ni and Cu). Thermomagnetic curves, hysteresis parameters, specific magnetic susceptibility χ, frequency-dependent magnetic susceptibility κ FD%, magnetic remanence and saturation isothermal remanent magnetization ratios (i.e., S and SIRM/χ) reveal the presence of mostly fine-grained magnetite and maghemite in these samples. The Tomlinson Pollution Load Index (PLI), as well as the magnetic parameters χ, κ FD%, SIRM/χ and S-ratios, vary more or less in agreement to each other when they are sequentially arranged throughout a 30-km-long transect that goes from the town of Carballo to the river mouth in Ponteceso. From that profile, it is possible to identify an anomaly of χ that lies between two small peaks of the PLI and seems to define a contaminated area probably linked to a diffuse low-impact source of pollution. There is also a conspicuous peak of the PLI that is likely associated to a nearby gold mine. The variations of the κ FD%’s along the transect are the ones that best reflect the changes in the PLI values, regardless of the level of contamination. This result suggests that adsorption is the main mechanism of trace elements removal by Fe oxides in these samples. Direct signal analyses, used to decompose the isothermal remanent magnetization curves, reveal the presence of four magnetic fractions, with varying relative concentrations all over the profile, namely single-domain magnetite, close to the superparamagnetic threshold (SD/SP) and/or maghemite ( $$\log B_{1/2}$$ ca 1.2), single-domain magnetite ( $$\log B_{1/2}$$ ca 2), hematite ( $$\log B_{1/2}$$ ca 2.5) and goethite ( $$\log B_{1/2}$$ ca 3.5). Integrating all the available information, it was sketched out a likely sequence of events that included magnetic minerals neoformation in parent soils, their subsequent chemical transformations and the contamination episodes that affected the region.

Frequency dependence of magnetic susceptibility as a proxy for fine-grained iron minerals and aggregate stability of south Chilean volcanic ash soils

Aggregate stability (AS) is an important property controlling erodibility of volcanic ash soils and is known to be strongly affected by fine-grained iron (Fe) and aluminum (Al) minerals. Assuming that frequency dependence of magnetic susceptibility (MS) is related to the amount of fine-grained Fe minerals and considering that formation of fine-grained Fe and Al minerals is closely coupled in volcanic ash soils, we hypothesized that the measurement of MS can be used to evaluate AS of these soils. To verify this, we investigated volcanic ash soils along a 120-km transect in southern Chile, reaching from the Andean Southern Volcanic Zone (SVZ) to the Pacific coastal range. Stability of 1-cm macroaggregates from topsoil (0–5cm) and subsoil (20–25cm) was determined by wet-sieving, combining long-term water immersion and subsequent ultrasonic treatment. MS was measured at 465 and 4650kHz to calculate its frequency dependence. We found an increasing amount of organic matter, fine-grained Fe and Al minerals, and clay and decreasing bulk density with increasing distance from the SVZ, indicating progressing soil development along the transect. Likewise, AS increased with increasing distance from the SVZ and was found to be controlled primarily by soil organic matter and fine-grained Fe and Al minerals. While MS itself showed only slight variation, its frequency dependence continuously increased with increasing distance from the SVZ, indicating an increasing fraction of fine-grained ferrimagnetic particles. Accordingly, frequency dependence of MS was found to be linearly related to the amount of fine-grained Fe minerals as quantified by dithionite extraction, and moreover, due to the close linear relationship between fine-grained Fe and Al phases, it revealed to be suitable for estimating the total amount of both fine-grained Fe and Al minerals. Analysis of underlying material (60–65cm) indicated that the increase in frequency dependence of MS with increasing distance from the SVZ was caused by fine-grained ferrimagnetic particles of pedogenic and lithogenic origin. Although overall organic matter content turned out to be more closely related to the stability of the investigated aggregates, we conclude that frequency dependence of MS can be used as an easily obtainable proxy for assessing the contribution of fine-grained Fe and Al minerals to AS.

Cyclostratigraphic analysis of magnetic records for orbital chronology of the Lower Cretaceous Xiagou Formation in Linze, northwestern China

In this study, we report a tuned astronomical time scale for a sedimentary formation in Early Cretaceous – the lower Linze Section located in the Zhangye Basin of the central Hexi Corridor, northwestern China. Based on detailed field investigations, we identified this sediment as the Xiagou Formation, which is widely distributed in the region. A thick, prominent limestone layer crops out in the middle portion of the Linze Section, and can be correlated to a similar limestone layer in the Liupanshan Group, which has been dated via high-resolution magnetostratigraphy. This correlation places an age constraint of around 114Ma for the top of the underlying strata. A total of 1245 samples were collected from the 474-m-thick lower Linze Section, for magnetic susceptibility measurements and cyclostratigraphic analysis. Spectral and continuous wavelet analyses were applied to the low-frequency magnetic susceptibility series and the percentage frequency-dependent magnetic susceptibility series, as well as to specific subsections exhibiting visible rhythmic bedding. A hierarchy of sedimentary cycles was identified, with wavelengths of 21.5–37.0m, 7.5–9.5m, 2.1–4.4m, and 1.4–1.7m. The ratios between these lengths correspond well to the ratios between the durations of Earth's orbital long-eccentricity, short-eccentricity, obliquity, and precession cycles. We interpret these sedimentary cycles to reflect the effects of orbital forcing on sedimentary processes. Using band-pass filtering to specifically extract eccentricity cycles, we established a tuned astronomical time scale for the Xiagou Formation in the lower Linze Section, with a total duration of about 6.1Myr (114.1Ma to 120.2Ma). Based on this timescale, the sedimentation rate of the Xiagou Formation is estimated to be in the range of 62–105m/Myr, with most intervals yielding rates in the 70–80m/Myr range.

Magnetic susceptibility of surface soils in the Mu Us Desert and its environmental significance

Abstract Magnetic susceptibility has been widely used as a climatic proxy in paleoclimatic research. In arid and semi-arid regions, the magnetic properties of modern surface soil are significantly influenced by precipitation. This is demonstrated by observed positive correlations between percentage frequency-dependent magnetic susceptibility (χ fd %), which reflects the presence of fine-grained (superparamagnetic, SP) grains produced during weathering and pedogenesis, and regional mean annual precipitation (MAP). To further investigate this relationship, we measured the magnetic properties of 104 surface soil samples collected along two transects (AA and BB) spanning a rainfall gradient across the Mu Us Desert in northern China. There were no systematic trends in magnetic properties along transect BB; the χ fd % values remained relatively low and stable, probably reflecting weak pedogenesis and the domination of the magnetic properties by lithology. In contrast, along transect AA there was a significant positive correlation (p fd % and regional MAP. From this relationship, we developed a transfer function (P = 274.1 + 1424.4 × χ fd %) and used it to produce quantitative estimates of paleo-precipitation within three Holocene aeolian sections located in the southern the modern Mu Us Desert. The results show that the variations of reconstructed precipitation are consistent with those of lithological properties, and they also confirm previous conclusions that paleosol development in the study area is dominated by precipitation. Overall the results further demonstrate the feasibility of using frequency-dependent magnetic susceptibility to quantitatively reconstruct regional paleo-precipitation, including within a geographically diverse desert area. In addition, they provide an improved understanding of the main sand provenance in Mu Us Desert.

Heavy metals pollution assessment in correlation with magnetic susceptibility in topsoils of Shanghai

This study investigated the heavy metal accumulation, magnetic susceptibility, and their correlation in urban soils of Baoshan District, Shanghai. A total of 127 topsoil samples were collected from industrial (n = 28), roadside (n = 38), residential (n = 21), and agricultural (n = 40) areas. The absolute concentration of heavy metals: lead (Pb), zinc (Zn), chromium (Cr), nickel (Ni), cadmium (Cd), and copper (Cu), was measured using an atomic absorption spectroscopy (AAS). Nemerow pollution index was applied to estimate the pollution level in respective areas. The results showed an excess of heavy metals in the urban topsoil of Baoshan District, among which, Pb, Zn, and Cd were most prominent. The average values of Pb, Zn, and Cd were obtained as 118.5, 228.6, and 0.56 mg kg−1, respectively, which are 5.6, 3.0, and 2.8 times higher than the Shanghai soil background values. Kriging interpolation was employed (according to the pre-evaluated fitted model variogram values of nugget, sill, and range) to assess the spatial distribution of heavy metals. Kriging interpolation depicted that the industrial sites were heavy metal-centric locations. Complimentary to AAS detection method, magnetic susceptibility tool was also applied to evaluate the presence of magnetic particles and their correlation with heavy metals. The magnetic susceptibility of the topsoil in Baoshan District was 148 × 10−8 m3 kg−1, which is ~5 times higher than the background value of Shanghai soil (29.1 ± 9.8 × 10−8 m3 kg−1). In most of the samples, the percentage frequency-dependent magnetic susceptibility (χ fd%) values in the topsoil of Baoshan District were less than 4%, suggesting the absence of pedogenic ultrafine superparamagnetic grains and the presence of anthropogenic multidomain and stable single domain grains. A significantly positive correlation (industrial: r = 0.81, P < 0.01; roadside: r = 0.65, P < 0.01; residential: r = 0.56, P < 0.01; agricultural: r = 0.6, P < 0.01) was found between magnetic susceptibility and heavy metal pollution irrespective of the type of anthropogenic activities at a particular land. The results suggested the reliability of magnetic susceptibility measurement to interpret the heavy metal pollution of the soils.

Application of magnetic methods for assessment of soil restoration in the vicinity of metallurgical copper-processing plant in Bulgaria.

Copper ore mining and processing are among the most harmful anthropogenic influences for the environment and they are a subject of international and national law regulations. Recultivation of areas influenced by mining and processing industry is commonly applied and monitored in order to restore as much as possible the natural environment. In this study, environmental magnetic methods are applied in order to assess the degree of soil restoration in terms of soil development, after remediation of waste dump from Cu-processing plant. Soils developed under birch forest stands of different age (5, 15, and 25years) as well as raw waste material were sampled along depth down to 20-30cm. Variations in magnetic parameters and ratios obtained (magnetic susceptibility, frequency-dependent magnetic susceptibility, anhysteretic remanence (ARM), isothermal remanence (IRM), ARM/IRM100mT) suggest the presence of magnetic enhancement in the upper 0-15cm, the thickness of this layer varying depending on the age of the forest stand. Magnetic mineral responsible for this enhancement is of magnetite type, while waste material contains a large amount of hematite, as evidenced by coercivity analysis of IRM acquisition curves and thermal demagnetization of composite IRM. Magnetic grain-sized proxy parameters suggest that magnetite particles are coarser, magnetically stable, while no or minor amount of superparamagnetic grains were detected at room temperature. A well-defined linear regression between the topsoil magnetic susceptibility and the approximate age of the forest stand provides an indication that the magnetic enhancement is of pedogenic origin. It is concluded that the observed magnetic enhancement of recultivated soils studied is linked to a combined effect of pedogenic contribution and possible additions of industrial ashes as a liming agent for soil restoration.

Magnetic Characteristics and Environmental Pollution Analysis of Street Dust in Different Functional Zones of Xi'an City

Urban environmental pollution can be revealed by the magnetic characteristics of street dust. Environmental magnetic measurements were carried out for the 151 samples of street dust collected in different functional zones of Xi'an city. Magnetic susceptibility varied within the range between 169.5×10-8 m3·kg-1 and 977.48×10-8 m3·kg-1, and the χlf average value was 415.66×10-8 m3·kg-1,which was 10 times higher than that of the background value. Isothermal remanent magnetization varied within the range between 2005.31×10-5 A·m2·kg-1 and 10897.64×10-5 A·m2·kg-1, and the SIRM average value was 5105.99×10-5 A·m2·kg-1. The average value of frequency-dependent magnetic susceptibility was 1.30, which was extremely low. The SIRM curve was consistent with χlf curve. The results indicated a high concentration of magnetic minerals in street dust. The magnetic minerals were mainly low-coercivity ferrimagnetic (magnetite and maghemite) and anti-ferromagnetic minerals (hematite), which contributed to the magnetic susceptibility. The main domains of magnetic minerals were composed of multiple domain (MD) and pseudo-single domain (PSD) ferrimagnetic minerals demonstrating the pollution of environment. According to the spatial distribution of magnetic properties of street dust and the different functional zones of Xi'an city, seven districts (A, B, C, D, E, F and G areas) were divided, which were summarized as three pollution types:heavily polluted, moderately polluted and lightly polluted. In the ecological district of Baqiao (F area) which was heavily polluted, χlf, SIRM and soft values were all the highest in the seven areas, and the main pollution sources were industry and vehicle emission. χlf, SIRM and soft values were slightly higher in the high-tech industrial district (A area) and the central business and commerce district (B area), which was moderately polluted by industry and vehicle emission. However, the magnetic parameters were relatively low in the functional zones of education, tourism and culture (C, D, E and G area), demonstrating that these areas were only slightly polluted by vehicle emission.

Photoluminescent and Slow Magnetic Relaxation Studies on Lanthanide(III)-2,5-pyrazinedicarboxylate Frameworks.

In the series described in this work, the hydrothermal synthesis led to oxidation of the 5-methyl-pyrazinecarboxylate anion to the 2,5-pyrazinedicarboxylate dianion (2,5-pzdc) allowing the preparation of three-dimensional (3D) lanthanide(III) organic frameworks of formula {[Ln2(2,5-pzdc)3(H2O)4]·6H2O}n [Ln = Ce (1), Pr (2), Nd (3), and Eu (4)] and {[Er2(2,5-pzdc)3(H2O)4]·5H2O}n (5). Single-crystal X-ray diffraction on 1-5 reveals that they crystallize in the triclinic system, P1̅ space group with the series 1-4 being isostructural. The crystal structure of the five compounds are 3D with the lanthanide(III) ions linked through 2,5-pzdc2- dianions acting as two- and fourfold connectors, building a binodal 4,4-connected (4·648)(426282)-mog network. The photophysical properties of the Nd(III) (3) and Eu(III) (4) complexes exhibit sensitized photoluminescence in the near-infrared and visible regions, respectively. The photoluminescence intensity and lifetime of 4 were very sensitive due to the luminescence quenching of the 5D0 level by O-H oscillators of four water molecules in the first coordination sphere leading to a quantum efficiency of 11%. Variable-temperature magnetic susceptibility measurements for 1-5 reveal behaviors as expected for the ground terms of the magnetically isolated rare-earth ions [2F5/2, 2H4, 4I9/2, 7F0, and 4I15/2 for Ce(III), Pr(III), Nd(III), Eu(III), and Er(III), respectively] with MJ = 0 (2 and 4) and ±1/2 (1, 3, and 5). Q-band electron paramagnetic resonance measurements at low temperature corroborate these facts. Frequency-dependent alternating-current magnetic susceptibility signals under external direct-current fields in the range of 100-2500 G were observed for the Kramers ions of 1, 3, and 5, indicating slow magnetic relaxation (single-ion magnet) behavior. In these compounds, τ-1 decreases with decreasing temperature at any magnetic field, but no Arrhenius law can simulate such a dependence in all the temperature range. This dependence can be reproduced by the contributions of direct and Raman processes, the Raman exponent (n) reaching the expected value (n = 9) for a Kramers system.

Detection of the pedogenic magnetic fraction in volcanic soils developed on basalts using frequency-dependent magnetic susceptibility: comparison of two instruments

Abstract In studies of the magnetic properties of soils, the frequency-dependent magnetic susceptibility percentage (χFD%) is often used for the identification of ultrafine magnetically superparamagnetic/stable single-domain (SP/SSD) particles. This parameter is commonly used as an indicator for increased pedogenesis. In strongly magnetic soils, the SP/SSD magnetic signal (mostly bio-pedogenic) may be masked by lithological signals; making pedogenesis hard to detect. In this study, we compare results for the detection of ultrafine SP/SSD magnetic particles in andic soils using two instruments: a Bartington MS2B dual-frequency meter and an AGICO Kappabridge MFK1-FA. In particular, the study focuses on the effect of pedogenesis by investigating the relationship between specific soil magnetic and chemical properties (soil organic carbon and pHH2O). The values of χFD% obtained with the MS2B varied from 2.4 to 5.9 per cent, and mass-specific magnetic susceptibility (χLF) from 283 to 1688 × 10−8 m3 kg−1, while values of χFD% and χLF obtained with the MFK1-FA varied from 2.7 to 8.2 per cent and from 299 to 1859 × 10−8 m3 kg−1, respectively. Our results suggest that the detection of the SP/SSD magnetic fraction can be accomplished by comparing relative trends of χFD% along the soil profile. Moreover, the discrimination between bio-pedogenic and lithogenic magnetic contributions in the SP/SSD fraction is possible by comparing the χFD% and χLF data determined in the fine earth (&amp;lt;2 mm) and the coarse fraction (4–10 mm) samples down the soil profile.

Environmental magnetism: Application to cave sediments

Environmental magnetism techniques allow a rapid, low cost and sensitive characterization of sediments and can be applied in a wide range of environments. More specific, magnetic properties can be successfully used to reconstruct paleoenvironmental and paleoclimatic conditions in rockshelter and cave sites. Cave sediments, imprint the environmental conditions at the Earth’s surface at the time of deposition since are well protected both at the interior and at the entrance of the cave systems. In addition, many cultural sequences and archaeological artifacts are well preserved in rockshelter and cave sediment records and can be effectively used for paleoenvironmental interpretations. In this study we present data from two different cave sites from Northern Greece. In the first cave (Maronia Cave) magnetic measurements were performed in two cores 80 and 90 cm, respectively, located inside the cave area. High values of magnetic susceptibility are directly linked with the human activity inside the cave, while lower values show deposition under infiltration and fluvial processes. In the second cave (Mikro Eptamilon Cave), magnetic susceptibility and frequency dependent magnetic susceptibility depicted from a sedimentary sequence with a thickness of 200 cm, located in the entrance of the cave. Results lead to conclusions concerning the velocity of the paleo-flow likely related to the paleoclimatic conditions that dominated the broader area.

Effect of magnetic dipolar interactions on temperature dependent magnetic hyperthermia in ferrofluids

Magnetic hyperthermia (MHT), where localized heating is generated when magnetic nanoparticles (MNPs) are subjected to a radiofrequency magnetic field, has a great potential as a non-invasive cancer therapy treatment. The efficiency of heat generation depends on the magnetic properties of MNPs, such as saturation magnetization (Ms) and magnetic anisotropy (K), as well as the particle size distribution and magnetic dipolar interactions. We have investigated MHT in two Fe3O4 ferrofluids prepared by co-precipitation (CP) and hydrothermal (HT) synthesis methods showing similar physical particle size distribution (14 ± 4 nm) and saturation magnetization (70 ± 2 emu/g of Fe3O4) but very different specific absorption rates (SAR) of ∼110 W/g and ∼40 W/g at room temperature (measured with an ac magnetic field amplitude of 240 Oe and a frequency of 375 kHz). This observed reduction in SAR has been explained by taking into account the dipolar interactions and the distribution of the magnetic core size of MNPs in ferrofluids. The HT ferrofluid shows a higher effective dipolar interaction and a wider distribution of the magnetic core size of MNPs compared to those of the CP ferrofluid. We have fitted the temperature dependent SAR data using the linear response theory, incorporating an effective dipolar interaction, to determine the magnetic anisotropy constant of MNPs prepared by CP (22 ± 2 kJ/m3) and HT (26 ± 2 kJ/m3) synthesis methods. These values are in good agreement with the magnetic anisotropy constant determined using frequency and temperature dependent magnetic susceptibility data obtained on powder samples.

ПЕРШІ РЕЗУЛЬТАТИ ЕКОМАГНІТНИХ ДОСЛІДЖЕНЬ СЛАБКОУРБАНІЗОВАНИХ МІСТ НА ПРИКЛАДІ ТРУСКАВЦЯ (УКРАЇНА) ТА МОНПЕЛЬЄ (ФРАНЦІЯ)

The objective of the present study is the assessment of the general trends for the pollution level of slightly impacted urban environment based on energy-efficient technology. The implementation of this approach is proposed on the examples of Truskavets (Ukraine) and Montpellier (France). The ultimate goal is to produce the preliminary data of the pollution with magnetic measurements. Regarding the anthropogenic pollution of the studied area the slight level of the urbanization must be accepted. The first source of the pollution is the road traffic and the second one is the railway and trams network. Non-urbanized landscape of Truskavets is presented by the forests. The soil types are gleysols. The urbanized soils of Truskavets and Montpellier are the urbozems. The magnetic susceptibility for the non-polluted soil in Truskavets is up to 8-10×10-8 m3/kg, very low values for Ukrainian soils, were registered. At the same time the polluted soils collected from the profiles and under the areal researches near the roadway and railway are characterized by a much higher MS: χ=36-162×10-8 m3/kg. The pollution of the soils were confirmed by the frequency dependence of magnetic susceptibility with the values of χfd= 2-3. The tree leaves from the Montpellier have much higher isothermal remanence along the roadway and tram line comparing with the natural area. The magnetic mineralogical analyses included thermomagnetic studies, hysteresis and remanence acquisition, ARM, and S ratio. The magnetite-like phase as the main magnetic mineral responsible for the magnetic enchantments in polluted soil was identified. At the same time non-polluted soil may contain the small amount of the single-domain (SD) particles and the high coercivity minerals such as haematite and goethite. Our results are valuable for the environmental management companies, centers of environmental monitoring, and geophysical observatories. Low cost, non-destructive and rapid magnetic techniques are promising in monitoring soil and air pollution both in highly anthropogenic impacted areas and at the slightly urbanized sites.

Syntheses, structures and magnetic properties of the lanthanide complexes of the pyrimidyl-substituted nitronyl nitroxide radical.

Four 2p-4f LnIII-radical complexes, [(NIT-2-Pm)Ln(hfac)3]·0.5C7H16 (NIT-2-Pm = 2-pyrimidyl-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxy-3-oxide, hfac = hexafluoroacetylacetonato, Ln = Tb (1), Dy (2), Ho (3) and Er (4)), and four 4f-2p-4f LnIII-radical-LnIII complexes, [(μ-NIT-2-Pm)Ln2(hfac)6(H2O)2]·0.5C7H16 (Ln = Tb (5), Dy (6), Ho (7) and Er (8)) have been synthesized and characterized structurally and magnetically. These compounds can be selectively obtained by controlling the reaction ratio of Ln(hfac)3·2H2O to the radical ligand NIT-2-Pm. The crystal structures show that in the former four complexes 1-4, the NIT-2-Pm radical acts as a terminal bidentate ligand chelating to one LnIII ion, while in 5-8, the NIT-2-Pm acts as a bridging ligand linking two LnIII ions to form a binuclear three-spin system. Magnetic studies revealed that complexes 1-4 and 6 show frequency-dependent ac magnetic susceptibilities, suggesting a possible single-molecule magnet behavior. To the best of our knowledge, complexes 3 and 4 are the first Ho-NIT and Er-NIT compounds showing slow magnetic relaxation. Compounds 5-8 represent a rare family of compounds showing the NIT bridged 4f-2p-4f three-spin motif, while complex 6 is a rare NIT bridged multinuclear lanthanide compound possessing SMM-like behaviour. Ab initio calculations were performed on all these complexes. The fitting of the magnetic susceptibilities of these compounds suggests weak antiferromagnetic coupling between the LnIII and NIT radical in 1-8 and weak ferromagnetic LnIII-LnIII interactions in 5-8.

Millennial scale climate oscillations recorded in the Lower Danube loess over the last glacial period

In this study we provide a correlative age model for last glacial loess at the Rasova-Valea cu Pietre site in the Lower Danube region, based on the correlation of palaeoenvironmental proxies to independently dated palaeoclimate archives, luminescence dating and independent age control provided by the geochemically confirmed presence of the Campanian Ignimbrite (CI) tephra. The CI tephra, originating in the Phlegrean fields of southern Italy, has been dated elsewhere by 40Ar/39Ar to 39–40ka BP, and is frequently found in the Lower Danube loess. As such, the CI tephra represents a valuable temporal and stratigraphic maker across loess deposits in the region. Our age model facilitates high-resolution correlation of palaeoenvironmental features observed at Rasova to palaeoclimate archives in Greenland and the Black Sea – Mediterranean area. We observe semi-cyclic behaviour of the frequency dependent magnetic susceptibility throughout the profile, which we ascribe to millennial-scale climate variability also observed elsewhere in the Black Sea region. This is the first study to clearly identify millennial-scale climate variability over the Holocene and last glacial in the Lower Danube loess. Proxy variability in the Holocene indicates continuous aeolian sedimentation through this epoch.

The Nature of the Bridging Anion Controls the Single-Molecule Magnetic Properties of DyX4M 12-Metallacrown-4 Complexes.

A family of DyX4M(12-MCMnIII(N)shi-4) compounds were synthesized and magnetically characterized (X = salicylate, acetate, benzoate, trimethylacetate, M = NaI or KI). The bridging ligands were systematically varied while keeping the remainder of the MC-geometry constant. The type of monovalent cation, necessary for charge balance, was also altered. The dc magnetization and susceptibility of all compounds were similar across the series. Regardless of the identity of the countercation, the Dy(Hsal)4M 12-MC-4 compounds were the only compounds to show frequency-dependent ac magnetic susceptibility, a hallmark of single-molecule magnetism. This indicates that the nature of the bridging ligand in the 12-MCMnIII(N)shi-4 compounds strongly affects the out-of-phase magnetic properties. The SMM behavior appears to correlate with the pKa of the bridging ligand.

The influence of interparticle correlations and self-assembly on the dynamic initial magnetic susceptibility spectra of ferrofluids

Using computer simulations and a mean-field theoretical approach, we study how the growth in dipolar interparticle correlations manifests itself in the frequency-dependent initial magnetic susceptibility of a ferrofluid. Our recently developed theory gives the correct single-particle Debye-theory results in the low-concentration, non-interacting regime; and it yields the exact leading-order contributions from interparticle correlations. The susceptibility spectra are analysed in terms of the low-frequency behaviours of the real and imaginary parts, and the position of the peak in the imaginary part. By comparing the theoretical predictions to the results from Brownian dynamics simulations, it is possible to identify the conditions where correlations are important, but where self-assembly has not developed. We also provide a qualitative explanation for the behaviour of spectra beyond the mean-field limit.

Microwave synthesis of high-quality and uniform 4 nm ZnFe2O4 nanocrystals for application in energy storage and nanomagnetics.

Magnetic nanocrystals with a narrow size distribution hold promise for many applications in different areas ranging from biomedicine to electronics and energy storage. Herein, the microwave-assisted sol–gel synthesis and thorough characterization of size-monodisperse zinc ferrite nanoparticles of spherical shape is reported. X-ray diffraction, 57Fe Mössbauer spectroscopy and X-ray photoelectron spectroscopy all show that the material is both chemically and phase-pure and adopts a partially inverted spinel structure with Fe3+ ions residing on tetrahedral and octahedral sites according to (Zn0.32Fe0.68)tet[Zn0.68Fe1.32]octO4±δ. Electron microscopy and direct-current magnetometry confirm the size uniformity of the nanocrystals, while frequency-dependent alternating-current magnetic susceptibility measurements indicate the presence of a superspin glass state with a freezing temperature of about 22 K. Furthermore, as demonstrated by galvanostatic charge–discharge tests and ex situ X-ray absorption near edge structure spectroscopy, the as-prepared zinc ferrite nanocrystals can be used as a high-capacity anode material for Li-ion batteries, showing little capacity fade – after activation – over hundreds of cycles. Overall, in addition to the good material characteristics, it is remarkable that the microwave-based synthetic route is simple, easily reproducible and scalable.