Low-field Magnetic Susceptibility Measurements Research Articles

Initial results of the colorimetric indices of the oldest exposed pedocomplex (Titel loess plateau, Serbia)

n this study we present an in-depth description of the colorimetric values for the lowest section of the Dukatar Loess Palaeosol Sequence (LPS) pedocomplex S5. Formed during the Marine Isotope Stage (MIS) 13-15, it represents the oldest pedocomplex exposed at the base of the Titel loess plateau (TLP), near the confluence of the Tisa and Danube rivers in Vojvodina (northern Serbia). The results of low-field magnetic susceptibility measurements (χlf) were compared to colour properties (obtained by conventional methods as well as instrumental measuring) and quantified Soil Development Indices (SDI). Of these measurements we found that the Redness Index (RI1) yielded the most useful results, as this index appears most sensitive to lithological changes and soil development intensity. It was also observed that a high level of correlation existed between χlf, and a* chromaticity. The initial results of this study highlight the utility of colorimetric methods as an interdisciplinary tool when evaluating the presence of ferromagnetics, and the application of rock magnetism to the Middle and Upper Pleistocene LPS of the Middle Danube Basin. The presented approach can be used to observe the evolution of climatic and ecological conditions in the given study area, and for establishing correlations between sites extending over the Eurasian LPS provinces.

Magnetic fabric and archaeomagnetic analyses of anthropogenic ash horizons in a cave sediment succession (Crvena Stijena site, Montenegro)

SUMMARY An archaeomagnetic, rock magnetic and magnetic fabric study has been carried out on seven anthropogenic ash horizons in the Middle Palaeolithic sedimentary level XXIV at the rock shelter of Crvena Stijena (‘Red Rock’), Montenegro. The study has multiple goals, including the identification of iron bearing minerals formed during combustion, assessment of the suitability of these combustion features for recording the Earth´s magnetic field direction, revelation of the magnetic fabric and its significance in the characterization of cave (rock shelter) burnt facies, and identification of post-burning alteration processes. Magnetite has been identified as the main ferromagnetic component of the ash. The ash layers exhibit a high thermomagnetic reversibility in contrast to the irreversible behaviour of their subjacent burnt black layers which is related to the different temperatures attained. Seven mean archaeomagnetic directions were obtained with acceptable statistical values indicating that these features recorded the field direction at the time of burning. However, some of them are out of the expected range of secular variation for mid-latitude regions suggesting post-burning alterations. The magnetic fabric of the ash was characterized by anisotropy of low field magnetic susceptibility measurements. Statistical analysis (box and whisker plot) of the basic anisotropy parameters, such as foliation, lineation, degree of anisotropy and the shape parameter, along with the alignment of the principal susceptibilities on stereoplots, revealed variation among the ash units. The diverse, oblate to prolate, lineated or strongly foliated, quasi-horizontally and vertically oriented fabrics of the units may indicate different slope processes, such as orientation by gravity, solifluction, run-off water, quasi-vertical migration of groundwater and post-burning/post-depositional alteration of the fabric by rockfall impact. In sum, the magnetic characterization of the ash layers has shown the occurrence of different post-burning alteration processes previously not identified at the site. Alteration processes in prehistoric combustion features are often identified from macroscopic observations but our study demonstrates that multiple processes can affect them and are usually unnoted because they take place on a microscopic scale. Their identification is critical for a correct chronological and cultural interpretation of a site (e.g. collection of samples for dating, stratigraphic displacement of remains), especially if significant alterations are involved. Magnetic methods are therefore a powerful but underutilized tool in palaeolithic research for the identification and evaluation of taphonomic processes affecting prehistoric fires.

Significant pedogenic and palaeoenvironmental changes during the early Middle Pleistocene in Central Europe

Three well-developed paleosols from the Paks loess succession (Hungary), a key profile of the European Loess Belt, were sampled and studied by rock magnetic methods, such as low-field magnetic susceptibility and hysteresis measurements. The studied paleosols formed in MIS19, MIS15 and MIS11 and represent key periods in the Middle Pleistocene, namely, the Middle Pleistocene transition (MPT) (MIS19), and frame the mid-Brunhes transition (MIS15 and 11).The results of the low-field magnetic susceptibility measurements, a popular interglacial intensity proxy, showed different patterns and values. The different characteristics of the susceptibility curve indicate different degrees of pedogenesis and therefore different soil-forming palaeoenvironments. The comparison of the rock magnetic (hysteresis) parameters supports the results of the susceptibility measurements and revealed some components of two characteristic palaeoclimate types: i.) a humid and warm MIS19 (pre-)MPT interglacial environment with very intense weathering and pedogenesis and ii.) a moderate climate with seasonal precipitation in a post-MPT interglacial environment during MIS15 and MIS11 characterized by intense but different types of pedogenesis compared to MIS19. This result, compared with other loess successions in the Middle and Lower Danube Basin and the western part of the East European Plain, helps to improve the climate model regarding the changing of the characteristic palaeoenvironment from a sub-Mediterranean (in the south) and temperate and humid climate (with forests, in the north) towards a cooler grassland/forest steppe-ruled environment in the region.

Thermomagnetic monitoring of lithic clasts burned under controlled temperature and field conditions. Implications for archaeomagnetism

We carried out a combined thermal and magnetic evaluation on experimentally knapped clasts of different lithologies (chert, quartzite, limestone, sandstone and obsidian) heated under controlled field and temperature conditions. The main aim of this study is to estimate the feasibility of use of these raw materials, which are commonly found in prehistoric archaeological sites for archaeomagnetic purposes. Rock magnetic analysis included measurements of low-field magnetic susceptibility, isothermal remanent magnetisation (IRM) acquisition curves, hysteresis loops and thermomagnetic curves of lithic clasts both before and after experimental heating. All lithologies, except the obsidian, recorded an increase of up two orders of magnitude in their magnetic concentration-dependent parameters revealing the formation of new ferrimagnetic minerals. Obsidian and sandstone are the most reliable magnetic carriers, followed by limestone, chert and quartzite. Magnetic susceptibility values show significant differences among lithologies. Isothermal remanent magnetisation proved also to be highly discriminatory as well as the room temperature hysteresis parameters. The main macroscopic alterations resulted in colour changes, rubefactions, potlids in cherts and the massive formation of internal fissures in obsidian specimens. The multispecimen palaeointensity technique was applied on selected samples yielding satisfactory results for heated obsidian and sandstone samples. The archaeological applicability of the results is discussed as well as their geomagnetic significance.

Use of Stevens coefficients for the prediction of magnetic transitions in pseudobinaryR1−xRx'Al2alloys: Application to Tm1−xTbxAl2

Recent heat-capacity and low-field magnetic susceptibility measurements revealed unusual magnetic phenomena occurring in Er${}_{1\ensuremath{-}x}$$R$${}_{x}$Al${}_{2}$ systems (where $R$ $=$ Dy,Tb) in the vicinity of a ``magic'' concentration of $x$ $=$ 0.25. Empirically, such behavior was attributed to different shapes of the 4f charge densities of the ${R}^{3+}$ ions, which are represented by the opposite signs of the second-order Stevens factors. Here we show that by using both the signs and magnitudes of the second- order Stevens factors, magnetic transitions can be predicted in a broader range of pseudobinary ${R}_{1\ensuremath{-}x}{R}_{x}^{'}$Al${}_{2}$ alloys, where $R$ and $R$\ensuremath{'} are rare-earth metals that have opposite signs of second-order Stevens factors. The predictions have been verified using the Tm${}_{1\ensuremath{-}x}$Tb${}_{x}$Al${}_{2}$ system as a model using x-ray diffraction, magnetic susceptibility, and heat-capacity measurements. First-principles calculations have also been performed to explore the behavior of the density of states near the Fermi level.

Frequency dependence of magnetic susceptibility of weakly contaminated soil sediments

This paper reports the frequency dependence of magnetic susceptibility of weakly contaminated soil sediments. Low field magnetic susceptibility measurements were carried out on soil sediments at Bomo irrigation dam, Samaru College of Agriculture, Ahmadu Bello University, (ABU), Zaria, using the MS2D field loop. Soil samples were also collected for laboratory analyses. The volumetric percentage composition of magnetite (Fe) in the soil was found to be about 0.02%. Frequency dependent magnetic susceptibility measured at two frequencies (0.465 kHz and 4.65 kHz) using MS2B sensor reveals a slight difference between magnetic susceptibility values with the higher frequency indicating lower values. The coefficient of frequency dependence (%) values varying between 2.37% and 7.39%, indicating the presence of a mixture of ultrafine superparamagnetic and coarse nonsuperparamagnetic grains or SP grains < 0.005 m ferromagnetic minerals occurring as crystals in the top soil. The soil formation process was as a result of secondary ferromagnetic minerals occurring as a result of burning, biochemical and authigenic processes in the area under investigation.

Changes in mean magnetic susceptibility and its anisotropy of rock samples as a result of alternating field demagnetization

Measurements of low-field magnetic susceptibility ( K) and its anisotropy (AMS) on different rock types during stepwise alternating field (AF) demagnetization in increasing fields revealed not only significant changes of the AMS principal susceptibilities, but also an increase of the mean magnetic susceptibility ( K m). Studied collections of loess/paleosol samples from different sections in Belgium, Bulgaria, China, Siberia and Tadjikistan and diorites, granites and gneisses from Antarctica show systematic K m-increase, between 2 and 27% as compared to the initial values, after AF-demagnetization up to 100 or 200 mT maximum amplitude. The relationships between magnetic susceptibility increase and magnetic hysteresis parameters and their ratios, indicate that the K m-increase is due to changes in magnetic domain configuration of the initial natural remanent magnetization (NRM) state of the remanence carriers during AF-treatment. The obtained linear relationship between K-increase and the degree of anisotropy P′ for strongly anisotropic gneiss samples suggests that magnetostatic interactions also play a role in the observed AF-effect on K m.

Investigation of Superconductivity in Isoelectronic and Related Compounds of MgB2

MgB 2 related compounds such as the borocarbides LiBC and MgB 2 C 2 , and the nominal compound of “BeB 2 ” were synthesized and existence of superconductivity investigated by low field magnetic susceptibility measurements. Superconductivity was observed not to occur in all of the compounds down to a temperature of 2 K which agrees with recent calculations on the borocarbides, Hole doping of MgB 2 C 2 has been predicted to be favorable for superconductivity due to the flat band (in the T–Y direction) similar to one in MgB 2 . Attempts to substitutionally hole dope MgB 2 C 2 with alkali metals were carried out for the first time, with Li doping demonstrated to appear to be feasible, but in the present samples superconductivity was not observed.

Low-frequency low-field magnetic susceptibility of ferritin and hemosiderin

Low-frequency low-field magnetic susceptibility measurements were made on four samples of mammalian tissue iron oxide deposits. The samples comprised: (1) horse spleen ferritin; (2) dugong liver hemosiderin; (3) thalassemic human spleen ferritin; and (4) crude thalassemic human spleen hemosiderin. These samples were chosen because Mössbauer spectroscopic measurements on the samples indicated that they exemplified the variation in magnetic and mineral structure found in mammalian tissue iron oxide deposits. The AC-magnetic susceptometry yielded information on the magnetization kinetics of the four samples indicating samples 1, 2, and 3 to be superparamagnetic with values of around 10 11 s −1 for the pre-exponential frequency factor in the Néel–Arrhenius equation and values for characteristic magnetic anisotropy energy barriers in the range 250–400 K. Sample 4 was indicated to be paramagnetic at all temperatures above 1.3 K. The AC-magnetic susceptometry data also indicated a larger magnetic anisotropy energy distribution in the dugong liver sample compared with samples 1 and 3 in agreement with previous Mössbauer spectroscopic data on these samples. At temperatures below 200 K, samples 1–3 exhibited Curie–Weiss law behavior, indicating weak particle–particle interactions tending to favor antiparallel alignment of the particle magnetic moments. These interactions were strongest for the dugong liver hemosiderin, possibly reflecting the smaller separation between mineral particles in this sample. This is the first magnetic susceptometry study of hemosiderin iron deposits and demonstrates that the AC-magnetic susceptometry technique is a fast and informative method of studying such tissue iron oxide deposits.

Last interglacial‐glacial climatic cycle in loess‐palaeosol successions of north‐western France

The loess series at St. Pierre‐les‐Elbeuf and St. Sauflieu are key successions for the western European Quaternary stratigraphy. The present study proposes a detailed record of the last interglacial‐glacial climatic cycle at St. Pierre and its integration into the synthetic pedosedimentary record of north‐western France using detailed correlations with the type sections of St. Sauflieu and Achenheim. Finally, comparisons with the marine isotope, Greenland GRIP chronologies and dust records are proposed. At St. Pierre, the pedostratigraphic and sedimentological analyses (total iron, organic matter, carbonate, grain size), in association with low field magnetic susceptibility measurements, demonstrate that this loess succession records the major climatic events of the Upper Pleistocene. The basal soil complex at St. Pierre is similar to those from the main successions of North (St. Sauflieu) or Northeast France (Achenheim). It shows a Bt horizon of brown leached soil, a deeply reworked grey forest soil and two isohumic steppe soils separated by a non‐calcareous loess layer. This loess level corresponds to the first aeolian event clearly observed in the succession and can be correlated with Marker II of the Central European stratigraphy located around the marine isotope stage (MIS) 5/4 boundary. The main aeolian sedimentation starts after the soil complex and ends with the top soil (brown leached soil). Finally, a good parallel is observed between the strongest peaks of the dust records of the ice cores and the main period of loess deposition in St Pierre‐lès‐Elbeuf occurring during MIS 2.

Structural, Transport, and Magnetic Properties of the Nd 1- xA xTiO 3 ( A = Ca, Sr, Ba) System Where 0 ≤ x ≤ 1

A series of perovskite Nd 1- x A x TiO 3 (A = Ca, Sr, Ba) compounds has been prepared by the dc-arc melting technique in the composition range 0 ≤ x ≤ ∼1.0. The substitution of Sr and Ba in NdTiO 3 results in structural phase transitions from orthorhombic ( Pbnm) to cubic ( Pm3 m). The Nd 1- x Ca x TiO 3 series remains orthorhombic throughout the range studied. Low field magnetic susceptibility measurements and remanent magnetic moment studies suggest that the Ti sublattice in the insulating Nd 1- x A x TiO 3 compounds (0 ≤ x ≤ ∼0.2) orders as canted antiferromagnets. The Nd 1- x A x TiO 3 compounds show compositionally dependent metal-insulator transitions that coincide with the disappearance of the magnetic ordering. The correlations between the structure and transport properties are discussed in terms of the Ti-O-Ti angle and Ti-O bond distance. The perovskite tolerance factor, t, is also shown to be a useful parameter to sort insulating and metallic phases in these compounds.

High Tc Magnetic Superconductors in Rare Earth (R) Barium Copper Oxide RBa2Cu3O7-δ

Superconductivity with critical transition temperature Tc near 90 K has been found in RBa2Cu3O7-δ compounds where R = Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu, and with Tc=56 K for R = La by electrical resistivity and low field magnetic susceptibility measurements. All compounds (except La) form in the orthorhombic, layered perovskite structure which is isomorphic to YBa2Cu3O7-δ. The lattice parameters of the compounds decrease in accordance with the metallic radii of the R trivalent ions. The electrical resistivity of the compounds studied (except for R = Nd) decreases with decreasing temperature and exhibit a sharp superconducting transition. Upper critical magnetic field Hc2 of the heavy R compounds (R from Dy to Yb) were measured and the highest initial slope |dHc2/dTc|Tc yet found for above 90 K superconductors was exhibited in TmBa2Cu3O7-δ with a value of 2.8 tesla/K.