Search

Relevance. It is known that sedimentary deposits in modern lakes with high sedimentation rates contain detailed paleoclimatic, paleobiological, paleoecological and magnetic records. The study of these parameters allow creation of paleoreconstructions and prediction of future climate behavior. Aim. To identify ecological and climatic events and trends during the Late Quaternary, based on magnetic properties of rocks. Some climate-dependent parameters are not properly used, we are showing that magnetic parameters are sensitive indicators of climate change. Object. Sediments of the Lake Kandrykul (Republic of Bashkortostan). Materials and methods. A set of petromagnetic studies was carried out, including measurements of magnetic susceptibility, normal remanent magnetization in external magnetic field of up to 1.5 T, as well as differential thermomagnetic analysis on induced magnetization and scanning electron microscopy on selected samples. Normal magnetization curves were used to set apart dia-/paramagnetic, ferromagnetic and superparamagnetic components. Results. Seismoacoustic studies showed that the lake bed is smooth, without sharp changes. The maximum water depth is about 16 m, the thickness of sediments reaches 7.5 m. Magnetic susceptibility was measured for three core columns, and the results show good correlation of this parameter between all the cores. Thermomagnetic analysis was used to determine magnetic minerals composition. The Day–Dunlop plot showed the presence of single, pseudo-single and multidomain grains. The authors determined the contribution of dia/para-, ferro-, and superparamagnetic components to the overall magnetic susceptibility. The paper considers the variations in magnetic susceptibility, para-, ferromagnetic components in the context of the Holocene climate changes. Conclusions. Variations in magnetic properties reflect climate changes (i.e. deposition environment). Six zones with different depositional conditions were distinguished based on magnetic susceptibility and its component changes. Additionally, zones with single-domain particles were highlighted based on hysteresis parameters variations. These zones most likely are associated with the remains of magnetotactic bacteria. Joint analysis of paramagnetic, ferromagnetic susceptibility and hysteresis parameters produced information on the effect of total humidity on the bioproductivity of the lake.

Relevance. Lake sediments contain the unique data on mineral composition and physical properties reflecting environmental and climate changes over the past millennia. These data are extremely important for understanding the environmental processes today and in the future. Magnetic minerals and properties are considered as essential to reconstruct sediment supply and climate fluctuations. Aim. To reveal magnetic susceptibility and coercive spectrometric parameters as relevant for lake cores stratification in accordance with climate terms. Object. Core of Lake Bannoe sediments (length is 512 cm). The age of the core is ~12.5 thousand years old. Materials and methods. The magnetic susceptibility was measured using MFK-1A Kappabridge (AGICO). The hysteresis parameters of the studied sedimentary deposits were determined using a coercive spectrometer (J_meter). Induced magnetization based differential thermomagnetic analysis was performed on an auto-registering magnetic torsion balance using the zero method. Results. The magnetic susceptibility of sediments taken from Lake Bannoe ranges from 0.88 to 7,87∙10-7m3/kg. Differential thermomagnetic analysis revealed the presence of magnetite in these sediments. The Day–Dunlop plot indicated that the magnetic grains in the samples of Lake Bannoe are a mix of single-domain and multi-domain (pseudo-single-domain) particles, with multi-domain grains comprising 70 to 92% of the total. Variations in magnetic susceptibility and its components were analyzed in relation to the Holocene climatic stages as defined by the Blytt–Sernander classification. Conclusions. It is found that the variations in magnetic properties of the studied sediments are in harmony with climate stages of the Holocene. Sediments of Lake Bannoe recorded the Bond event #8 (~11100 years ago), as well as regional aridization events which occurred ~4500 and ~2000 years ago. The results obtained during this study complement already existing paleoclimatology data, which will be interesting to a wide range of researchers – from paleoclimatologists to limnologists and ecologists.

In this work, we have studied the microstructure and unusual ferromagnetic behavior in epitaxial tin dioxide (SnO2) films implanted with 40 keV Co+ ions to a high fluence of 1.0 × 1017 ions/cm2 at room or elevated substrate temperatures. The aim was to comprehensively understand the interplay between cobalt implant distribution, crystal defects (such as oxygen vacancies), and magnetic properties of Co-implanted SnO2 films, which have potential applications in spintronics. We have utilized scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometry (VSM), differential thermomagnetic analysis (DTMA), and ferromagnetic resonance (FMR) to investigate Co-implanted epitaxial SnO2 films. The comprehensive experimental investigation shows that the Co ion implantation with high cobalt concentration induces significant changes in the microstructure of SnO2 films, leading to the appearance of ferromagnetism with the Curie temperature significantly above the room temperature. We also established a strong influence of implantation temperature and subsequent high-temperature annealing in air or under vacuum on the magnetic properties of Co-implanted SnO2 films. In addition, we report a strong chemical effect of ethanol on the FMR spectra. The obtained results are discussed within the model of two magnetic layers, with different concentrations and valence states of the implanted cobalt, and with a high content of oxygen vacancies.