Secondary Magnetization Components Research Articles

Late Paleozoic Remagnetization on the Western Slope of the Southern Urals: Age and Geotectonic Implications

The paper presents the results of paleomagnetic studies on numerous intrusive bodies of the Bashkirian megazone – a major tectonic zone of the Southern Urals. More than 70 intrusions in different parts of the Bashkirian megazone (in the northern, central and southern part of the structure) were sampled. The studied intrusions have Riphean age, however, like a significant part of the rocks of the Southern Urals, these intrusive bodies were remagnetized during the Late Paleozoic collision within the Urals fold belt. This article will discuss the secondary Late Paleozoic component of natural remanence magnetization. According to the paleomagnetic data obtained, the secondary Late Paleozoic component in most of the Bashkirian megazone is post-fold, i.e. formed after the completion of the main phase of fold deformations in the Southern Urals. A comparison of paleomagnetic directions obtained from intrusions in different parts of the Bashkirian megazone showed that there did not significant movements of individual parts of the Bashkirian megazone relative to each other after the formation of the Late Paleozoic component. The Late Paleozoic remanence component yielded a paleomagnetic pole of Plong = 171.6°, Plat = 39.9°, α95 = 5.9°, N = 6 from 6 areas (38 sites) in the Bashkirian megazone. The obtained pole is statistically indistinguishable from the mean of 15 poles for Stable Europe with ages of 280–301 million years. Thus, the secondary Late Paleozoic component in the Bashkirian megazone formed approximately 280–301 million years ago, after which the Bashkirian megazone did not experience any relative motions with respect to the East European craton.

Liftoff of a soft-actuated micro-aerial-robot powered by triboelectric nanogenerators

Aerial insects can nimbly navigate in cluttered natural environments while they interact with delicate objects such as flowers and leaves. To achieve insect-like agility and robustness, power dense dielectric elastomer actuators (DEAs) have been developed for driving sub-gram micro-aerial-vehicles (MAVs). However, despite exhibiting muscle-like bandwidth and resilience, DEAs require a high driving voltage in the range of 1 – 2 kilovolts. This requirement poses substantial challenges for developing compact boost electronics and energy sources, which prohibit power autonomous operations of soft-actuated sub-gram MAVs. Here, we develop a compact and high power triboelectric nanogenerator (TENG) that can effectively charge a high-voltage DEA and enable the liftoff of a soft-actuated MAV. We propose an In-plane Charge Pump (ICP) design that can deliver over 1500 V and 110 mW without requiring a secondary charge pump or magnetic circuit components such as inductors or transformers. Compared to conventional free-standing mode TENGs, our ICP design shows a 280 % and 920 % increase in voltage and energy generation, respectively. When this TENG powers a DEA-driven MAV, the 160 mg robot achieves liftoff with a lift-to-weight ratio of 1.75. This result highlights the potential of powering high-voltage microrobots with energy-harvesting devices.

LATE PALEOZOIC REMAGNETISATION AS AN INDEPENDENT INDICATOR OF TECTONIC PROCESSES IN THE SOUTHERN URALS

Analysis of secondary magnetization components (Late Paleozoic remagnetization) makes it possible to trace the formation of the Southern Urals folded system. The paper presents new data on the Late Paleozoic remagnetization of rocks in the Southern Urals. The results of the paleomagnetic study of rocks in various structural zones of the Southern Urals, obtained since 2009, were revised and supplemented again to identify the remagnetization component. Combined analysis of the newly obtained results and previously published data on Late Paleozoic remagnetization shows that in the western segment of the western slope of the South Urals the intermediate-temperature magnetization component (ITC) was acquired prior to or at the initial stages of deformation. In contrast, the ITC observed in the eastern segment arose after folding. In the western part of the Magnitogorsk zone in Devonian-age rocks, the average for all sites is post-folding. Deformations here occurred long before the final stage of the development of the Urals, most likely in late Devonian — early Carboniferous. In the Magnitogorsk-Bogdanovsky graben, in the early Carboniferous rocks, ITC has arisen during the process of deformation or shortly before it and at its initial stages. The Late Paleozoic remagnetisation identified in the paleomagnetic records is regional in nature and probably reflects a collisional event of the final stage of the evolution of the Ural Paleocean. Collision processes which occurred in the Southern Urals from the Late Devonian until the Late Permian time had undoubtedly left their trace in the western structures (in present-day coordinates). Within the passive margin of Baltica the collision resulted in the formation of a lateral series of fold-and-thrust structures. They started from the Main Uralian Fault westward, with possible gradual termination of this process towards the Pre-Uralian Foredeep. Paleomagnetic results of this research work support these assumptions.

Homotopy and adomian semi-numerical solutions for oscillatory flow of partially ionized dielectric hydrogen gas in a rotating MHD energy generator duct

Hydrogen-based MHD power generators offer significant advantages over conventional designs. The optimization of these energy devices benefits from both laboratory scale testing and computational simulation. Motivated by this, in the current work, a mathematical model is developed for MHD pumping of partially ionized hydrogen in a rotating duct with oscillatory, Maxwell displacement and magnetic induction effects under an inclined static magnetic field. Perfectly electrically conducting duct walls are assumed. The non-dimensional conservation equations are solved using the power-series based Homotopy Analysis Method (HAM) with an appropriate embedding parameter. Detailed graphical visualization of the impact of emerging parameters on the non-dimensional primary and secondary velocity components (u,v) and magnetic induction components (bx,by) across the duct is presented. Average squared residual errors for all key variables εu,εv,εbx,εby with associated CPU times at various orders of the HAM iteration are also included. Validation with an Adomian Decomposition Method (ADM) is also conducted, and excellent agreement is obtained (tabulated). The computations have shown that with increasing inverse Ekman number strong damping is observed in the primary flow whereas the secondary flow is accelerated, in particular in the core region of the duct. With elevation in Maxwell displacement effect (for the case of a 45° inclined magnetic field i.e. θ=π/4 ) there is a strong decrease in primary magnetic induction at the lower wall of the duct and elevation in magnitudes at the upper duct wall; however, in the core region no tangible modification is computed. The opposite trend is observed for the secondary magnetic induction. With increasing magnetic Prandtl number (i.e. ratio of magnetic Reynolds number to ordinary Reynolds number) in the presence of strong Maxwell displacement current, strong magnetic field and high inverse Ekman number, the primary velocity is accelerated in both the left and right half space of the duct with a dip in magnitude at the centreline. However, the secondary velocity exhibits a much lower enhancement in both zones with only weak acceleration near the duct walls. Both velocity components achieve symmetrical distributions about the duct centreline. A significant depletion in primary magnetic induction is computed near the lower duct wall with enhancement near the upper duct wall; the contrary behaviour is exhibited by the secondary induced magnetic field. Applications of the study arise in hybrid rotating hydrogen based MHD energy generators and furthermore the computations provide a good basis for generalization to 3-dimensional flows with commercial multi-physical fluid dynamic codes e.g. ADINA-F, COMSOL, ANSYS FLUENT-Maxwell wherein further phenomena may be explored including Alfven wave effects and dielectric losses.

ПАЛЕОМАГНЕТИЗМ ФАНЕРОЗОЙСКИХ ГЕОЛОГИЧЕСКИХ КОМПЛЕКСОВ ТУВЫ

The authors have investigated palaeomagnetically the Ordovician, Upper Devonian and Lower Carboniferous strata in Tuva. In the rocks, postfolding secondary and prefolding magnetization components were isolated. Paleomagnetic poles were calculated from primary magnetization components: for the Ordovician — Φ = 4° N, Λ = 307°E, A95 = 5.4°, if the Ordovician strata were formed in the Northern hemisphere and Φ = −41° N, Λ = 127°E, A95 = 5.4°, if the strata accumulated in the southern hemisphere; for the lower part of the Upper Devonian — Φ = 3.7° N, Λ = 139.8° E, A95 = 9.3°, for the upper part of the Upper Devonian — Φ = 51.7° N, Λ = 148.8° E, A95 = 16°; for the lower carbon — Φ = 53.8° N, Λ = 141.7° E, A95 = 9.6°. Probably, at least since the Ordovician, Tuva was part of the Siberian structure and was moving latitudinally with it. The Devonian and Lower Carboniferous strata are rotated in different degrees in the horizontal plane in relation to Siberia. The rotations could be associated with local deformations of rocks, but it is also possible that the rotation of a large geological block was caused by large-amplitude shifts after the Early Carboniferous.

Unblocking temperature of secondary magnetic component to outline anomaly thermomagnetic maps of archaeological fireplaces from the southern region of Mexico City, Mexico

We report a magnetic study of two preceramic hearths located at the southern region of Mexico City. Thermal demagnetization was applied between 200 to 540 °C to define the remanent magnetization components. The maximum unblocking temperature of the secondary magnetic component reached due to the last heating was identified in most samples. They were used to develop thermomagnetic anomaly source maps. The direction of this component was used to place the blocks to their last cooling spot and configurate a real and primal magnetic anomaly map produced by the thermoremanent magnetization acquired. A protocol to relocate blocks frame is proposed using geomagnetic secular variation curves. The thermomagnetic mapping revealed the position and temperature (220 to 460 °C) of the last heat sources. The distribution of these sources allowed to model an extensional zone of benefit and probable uses of the hearths.

New Discoveries on Electromagnetic Action and Signal Presentation in Magnetic Flux Leakage Testing

Based on the authors’ previous work of magnetic flux leakage (MFL) quantitative description and the research plan especially for the magnetic component of eddy current effect factor $$ B_{other} $$, further explorations for electromagnetic actions, magnetic and signal presentations in the defect in electromagnetic nondestructive testing (ENDT, such as direct current field measurement (DCFM), MFL and eddy current testing (ECT)) are continued here. Primarily, new discoveries indicate that the magnetic component of $$ B_{other} $$ is actually composed of the secondary magnetic field component of $$ \Delta B_{mfl} $$ which manifests as raised signal waves and volume current perturbation component of $$ \Delta B_{\Delta I} $$ which features as double peaked signals due to the departure or bypassing of the “volume current” in the defect. What’s more, the concrete expressions of magnetic components are deduced and given through Ampere’s (or the Ampere–Maxwell) law. Afterwards, the theory is well demonstrated and verified by means of finite element analysis for current density and magnetic flux density or MFL signals in typical quasi-static testing by DC magnetization for different specimens with defects. Additionally, suggestions for installation site of sensor elements in ENDT are also given. Finally, a unified evaluation standard for magnetic flux density is formed, which provides the basic theory or analysis principles for the ENDT techniques as well as research directions for precision defect detection and related applications.

Emplacement temperature resolution and age determination of Cerro Colorado tuff ring by paleomagnetic analysis, El Pinacate Volcanic Field, Sonora, Mexico

The lithic in the Cerro Colorado tephra deposits is dominated by clasts from shallow country rocks for a diatreme not well mixed, or, by a combination of material that reflects the relative proportions of country rock in a well-mixed diatreme. The clasts in a tephra ring bed might be ideal to use the paleomagnetic study to determine the emplacement temperature. We report emplacement temperature ranges of pyroclastic lithic fragments from the Cerro Colorado Tuff Ring in the El Pinacate Volcanic Field, Sonora, northwestern Mexico. Paleomagnetic analyses, particularly the thermoremanent magnetization procedure was carried out in 38 small cores, drilled from the 10 to 30 cm in size lithic fragments. It estimates the emplacement temperature ranges of the juvenile basaltic cauliflower bombs and not-juvenile diverse blocks produced in the phreatomagmatic eruption. Titanomagnetite and titanohematite are the main magnetic carriers, along with titanomaghemite. The 22 emplacement temperatures determined in this study are grouped in three temperature ranges, low (310–370 °C), medium (400–460 °C) and high (>500 °C). The low and medium temperature samples show two or more components, while the high temperature samples have, in general, only one component. This wide range of emplacement temperature could be related to the composite thermal history of the pyroclastic material incorporated in the water saturated pyroclastic flow deposit. The comparison of the mean direction of the secondary magnetization component with the secular variation curve of the global model SHA.DIF.14, suggests an age of 3915 ± 59 yr. BP.

Assessment of the Contribution of Secondary Metachronous Magnetization Components to the Precambrian Paleomagnetic Poles of the Karelian Craton

The secondary (metachronous) magnetization components identified in the Precambrian complexes of the Karelian Craton have been analyzed. The average directions of high-temperature components (deviations from the true direction) have been calculated based on the contribution of secondary magnetization components resulting from tectonomagmatic events of uneven ages. The Precambrian key poles often coincide with the vector sum of the Phanerozoic magnetization components of uneven ages. The conclusion on the primary/secondary origin of the Precambrian paleomagnetic poles should be made on the basis of the integrated petro- and paleomagnetic and isotope data and geological correlations, rather than based on only the paleomagnetic reliability tests.

Determination of contribution from the metachronous components of magnetization to the Precambrian paleomagnetic of the Karelian craton

The secondary (metachronous) component of magnetization isolated in the Precambrian complexes of the Karelian craton have been analyzed. The mean directions of high temperature components (deviations from the true direction) depending on the contribution of secondary magnetization components resulting from uneven-aged tectono-magmatic events. It has been shown that the Precambrian key poles often coincide with the vector sum of the ages of Phanerozoic component of magnetization. The conclusion about the primary/secondary origin of the Precambrian paleomagnetic poles must be set on the basis of the integrated petro-paleomagnetic and isotopic data and geological correlations, not only tests of paleomagnetic reliability.

New rock magnetic and paleomagnetic results for the 1.64 Ga Suomenniemi dyke swarm, SE Finland

This study represents new petrophysical and paleomagnetic data obtained for the 1.64 Ga Suomenniemi diabase and quartz porphyry dyke swarm associated with Suomenniemi rapakivi granite. We also present petrophysical data for the coeval dykes of the Sipoo (1.63 Ga) and Häme (1.642 ± 0.002 Ga; 1.647 ± 0.014 Ga) swarms in order to address: (1) the discrepancy between the coeval Sipoo and Häme poles and (2) the proposed severe overprint in paleomagnetic data for rapakivi related dyke swarms in Fennoscandia.Demagnetization of Suomenniemi dyke samples revealed dominantly normal polarity magnetization carried by magnetite. For the first time, a few samples from the few sites have shown a trace of a reversed magnetization. The combined normal (N) polarity direction from nine dykes (=sites) is at D = 031.2°, I = 07.2°, (with α95 = 10.6°, k = 21.8) yielding a paleomagnetic pole at Plat = 27.8°N; Plong = 171.7°E (with A95 = 7.9°, K = 38.4). The Suomenniemi pole fulfils four of the seven quality criteria for paleomagnetic poles (Van der Voo, 1990). The new pole for the Suomenniemi swarm is similar to the coeval Sipoo swarm pole, but distinctly different from the nearly coeval Häme swarm pole. The relative position of the poles compared to other well-defined paleomagnetic poles for Baltica indicates that the Suomenniemi and the Sipoo poles are slightly younger than the Häme pole.We show here that the original magnetization in some of the 1.64 Ga dykes in Suomenniemi have been overprinted with a secondary magnetization component, but several dykes of the swarm lack this overprint. Moreover, the presumably primary Subjotnian remanence component for the Suomenniemi dykes can be clearly isolated due to its different coercivity and/or unblocking temperature from the overprinted component. The same applies to the Sipoo and Häme dyke swarms.

Paleomagnetism of early paleozoic geological complexes of Mongolia

Most of the studied Early Phanerozoic rocks of West Mongolia have undergone repeated remagnetization. Secondary magnetization components with normal and reversed polarity are isolated. The magnetization components with normal polarity are associated with the Mesozoic remagnetization of the rocks. The components with reversed polarity were probably formed during the Carboniferous–Permian superchron of reversed polarity. The analysis of the distribution of the reversed-polarity magnetization component in the structure of Mongolia permits some zonation. Within Mongolia, the regions with insignificant post- Permian deformations and complicated post-Permian deformations are identified; also the area of rotations of large geological blocks about the horizontal axis (Khan-Khukhei Ridge) is distinguished. It is hypothesized that in the Ordovician rocks of West Mongolia, the magnetization component that is close to primary was identified. If this is the case, the paleolatitude calculated from this magnetization direction corresponds to the interval 14°–17°–20° (minimal–mean–maximal) of probably northern latitude

Complex remanent magnetization in the Kızılkaya ignimbrite (central Anatolia): Implication for paleomagnetic directions

Pyroclastic flow deposits, known as ash-flow tuffs or ignimbrites, are invaluable materials for paleomagnetic studies, with many applications for geological and tectonic purposes. However, little attention has been paid to evaluating the consistency and reliability of the paleomagnetic data when results are obtained on a single volcanic unit with uneven magnetic mineralogy. In this work we investigate this issue by concentrating on the Kızılkaya ignimbrite, the youngest large-volume unit of the Neogene ignimbrite sequence of the Central Anatolian Volcanic Province in Turkey, bringing evidence of significant magnetic heterogeneities in ignimbrite deposits (magnetic mineralogy, susceptibility, magnetic remanence, coercivity, etc.) and emphasizing the importance of a stratigraphic sampling strategy for this type of volcanic rocks in order to obtain reliable paleomagnetic data. Six sections were sampled at different stratigraphic heights within the devitrified portion of the ignimbrite. Isothermal remanence measurements point to low-Ti titanomagnetite as the main magnetic carrier at all sites; at some sites, the occurrence of oxidized Ti-magnetite and hematite is disclosed. The bulk susceptibility (km) decreases vertically at two out of six sections: its value for the topmost samples is commonly one order of magnitude lower than that of the samples at the base. In most cases, low km values relate to high coercivity of remanence (BCR) values, which range from 25 to >400mT, and to low S-ratios (measured at 0.3T) between 0.28 and 0.99. These data point to the occurrence of oxidized magnetic phases. We therefore consider the km parameter as a reliable proxy to check the ignimbrite oxidation stage and to detect the presence of oxidized Ti-magnetite and hematite within the deposit. The characteristic remanent magnetization is determined after stepwise thermal and AF demagnetization and clearly isolated by principal component analysis at most sites. For these sites, the site-mean paleomagnetic direction is consistent with data from the literature. At a few other sites, the remanence is more complex: the direction moves along a great circle during demagnetization and no stable end-point is reached. The occurrence of oxidized Ti-magnetite or hematite as well as two remanence components with overlapping coercivity and blocking temperature spectra suggest that the Kızılkaya ignimbrite acquired first a thermal remanent magnetization and then, during the final cooling or a short time later, a secondary remanent magnetization component which is interpreted as a CRM acquired during post-emplacement devitrification processes. Notwithstanding the Kızılkaya ignimbrite is a single cooling unit, its magnetic properties suffered substantial variations laterally and vertically within the deposit. The Kızılkaya case shows that thick pyroclastic deposits should be sampled using a stratigraphic approach, at different sites and different stratigraphic heights at each individual sampling location, otherwise, under-sampling may significantly affect the paleomagnetic results. When sampling is performed on a short duration or on very poorly preserved deposits we recommend drilling the lower-central portion in the most strongly welded and devitrified facies. Such sampling strategy avoids complications arising from the potential presence of a pervasive secondary CRM masking the original ChRM.

Paleomagnetism of Mongolia

Most Lower Phanerozoic rocks of western Mongolia investigated were repeatedly remagnetized. They demonstrate a secondary magnetization component of normal and reversed polarity. The normal polarity components are related to Mesozoic rock remagnetization. The reversed polarity components were probably formed during the Carboniferous‒Permian Superchron of reversed polarity. The analysis of the distribution of the reversed polarity component in the geological structure of Mongolia allows some zoning to be outlined with the defining regions of Mongolia characterized by insignificant rock defamations with intricate post-Permian dislocations and a region marked by rotation of large blocks around the horizontal axis (Khan Khukhei Range). It is assumed that Ordovician rock of western Mongolia contains a magnetization component close to the primary one. If the assumption is valid, the presumably northern paleolatitude derived from this direction corresponds to the interval of 14°‒17°‒20° (minimum‒average‒maximum, respectively).

Mesoproterozoic geomagnetic reversal asymmetry in light of new paleomagnetic and geochronological data for the Häme dyke swarm, Finland: Implications for the Nuna supercontinent

Baltica represents one of the key continents of the Mesoproterozoic supercontinent Nuna forming the core of it together with Laurentia and Siberia. This study presents new geochronological and paleomagnetic data obtained for the Häme diabase dyke swarm in southern Finland. New U-Pb (baddeleyite) ages 1642±2Ma and 1647±14Ma for two reversely magnetized dykes are acquired. Demagnetization revealed a dual polarity remanent magnetization direction carried by magnetite. The combined normal (N) and reversed (R) polarity direction for 11 dykes (=sites) is D=355.6°, I=−09.1° (k=8.6 and α95=16.6°) yielding a paleomagnetic pole at 23.6°N, 209.8°E (K=10.6 and A95=14.7°) with Van der Voo value Q=7. N and R magnetized units for the Häme dyke swarm show asymmetry in declination values, probably caused by an age difference between the dykes. The Geocentric Axial Dipole (GAD) model indicates that all geomagnetic reversals should be symmetric (in inclination), yet it has been noted that this is not always the case (e.g. 1.57Ga Satakunta and Åland dykes in Baltica). By analyzing global dual polarity paleomagnetic data we show that the stationary GAD model is a valid assumption at 1.7–1.4Ga and that the asymmetry between some normal and reversed polarities in global dual-polarity data sets appears randomly over time, and does not follow a global trend. Furthermore, we show that in the case of Åland and Satakunta dykes an unremoved secondary magnetization component could explain the obtained asymmetry. The GAD assumption is used to reconstruct the core of Nuna on equatorial latitudes using new data for Häme dykes. Paleomagnetic evidence suggest that maximum assembly of Nuna occurred at 1.5Ga and the dispersal of the core is proposed to be associated with coeval 1.38–1.27Ga magmatism in its core continents.

Paleomagnetic study on the Triassic rocks from the Lhasa Terrane, Tibet, and its paleogeographic implications

We present paleomagnetic results from the newly discovered Early-Middle and Late Triassic marine sediments of the Lhasa Terrane. Orientated samples were collected from 32 sites (330 samples) on the north side of the Dibu Co Lake (84.7°E, 30.9°N), Coqên County, in the western region of the Lhasa terrane. Rock magnetic data revealed that most of the samples were dominated by magnetite and/or pyrrhotite. The stepwise demagnetization curves illustrated three-components: a low temperature component (Component A) near the present-day field (PDF), a secondary remanent magnetization (Component B) that may be from the Cretaceous Period, and a high-temperature component (Component C). The Component C were isolated from the Early-Middle Triassic rocks in 8 sites (47 specimens) and from the Late Triassic rocks in 6 sites (37 specimens). The Component C of the Early-Middle Triassic rocks passed a reversal test (B class, 95% confidence level) and a fold test (99% confidence level), that of the Late Triassic rocks passed a fold test (95% confidence level). The corresponding paleopoles for the Early-Middle and Late Triassic periods of the Lhasa Terrane were at 18.9°N, 208.4°E with A95=3.9° and 19.6°N, 211.8°E with A95=10.7°, respectively. We suggest that the Lhasa Terrane maintained a relative stable latitude (16.5±3.9°S and 18.4±10.7°S) in the southern hemisphere during the Triassic Period before moving northwards and amalgamating with the main body of Eurasia. The Qiangtang and Lhasa terranes, which were located at the mid-low latitudes of the southern hemisphere, might have been isolated between Eurasia and Gondwanaland since the Early Triassic Period. The Meso-Tethys, potentially represented by the Bangong–Nujiang suture zone (BNS) between the Lhasa and Qiangtang terranes, opened up in the Early-Middle Triassic Period and expanded during the entire course of the Triassic Period.

Evidence for in-plane tetragonal c-axis in MnxGa1–x thin films using transmission electron microscopy

Tetragonal MnxGa1–x (x=0.70, 0.75) thin films grown on SrTiO3 substrates exhibit perpendicular magnetic anisotropy with coercive fields between 1 and 2T. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) reveal that 40nm samples grown at 300–350°C lead to films with the tetragonal c-axis oriented primarily perpendicular to the film plane but with some fraction of the sample exhibiting the c-axis in the film plane. This structure results in an undesirable secondary magnetic component in the out of plane magnetization. Growth at 300°C with a reduced thickness or Mn concentration significantly decreases the tetragonal c-axis in the film plane.

Controlling the magnetic characters co-existing at the novel nanometric multiferroic PrAlxFe1−xO3; 0.0 ⩽ x ⩽ 0.6 via an exchange bias interaction to open a new era of applications

For the first time, the nanometric multiferroic perovskites PrAlxFe1−xO3; 0.0⩽x⩽0.6, were synthesized and extensively studied. XRD results and tolerance factor calculations revealed the distorted orthorhombic single-phase structure for all synthesized samples. HRTEM micrographs for PrFeO3 (x=0.0) indicated homogeneous orthorhombic nanoparticles with high local crystallinity and highly ordered lattice planes. Interplanar d-spacing calculated from HRTEM accorded well with the d-values estimated from XRD. Introducing the undersized Al3+ cations to the B-site on the expenses of Fe3+ cations affected the crystallites’ size negatively and resulted in weak lattice inflation due to the BO6 octahedral tilting. As a result, PrAl0.1Fe0.9O3 (x=0.1) showed polycrystalline nature with deteriorated lattice arrangements, lower ordering and fair homogeneity. Magnetic hysteresis and DC molar magnetic susceptibility verified that this novel and unique series of nanometric multiferroics carries the antiferromagnetic (AFM) character as a secondary magnetic component inside all of its compositions. The existence of superparamagnetism (SPM) and ferromagnetism (FM) among selected x-values were also verified. PrFeO3 showed the superparamagnetic character, after which SPM to FM phase transition was established at x=0.1 with soft magnetic features and improved Ms, Mr and Hc values. Interesting magnetic hardening appeared at x=0.2 up to x=0.4 with further improvement of the magnetic constants. FM to AFM phase transition was reached at x=0.6 with the coexistence of the former two phases with different extents at 0.1⩽x-values⩽0.6. Competition between ferromagnetic and antiferromagnetic sub-lattices lead to a ferrimagnetic-like state and induced a phenomenon of exchange bias interaction which resulted in hysteresis necking at x=0.2 and 0.5. Our results are signatures of a complex magnetic structure considered as a magnetic core–shell-like system or a magnetic multilayer-like system with an exchange interaction between the FM/AFM heterosystems at their interfaces. Recorded Ms and Mr values exceed those reported in literature for RFeO3 multiferroics with weak ferromagnetic moment. Each sample in this series showed its own magnetic behavior and can be applied to a specific tailored application. New era of applications are expected for this new multiferroic series of perovskites as exchange bias materials.

Paleomagnetic study of Late Paleozoic rocks in the Tacheng Basin of West Junggar (NW China): Implications for the tectonic evolution of the western Altaids

To better understand the tectonic evolution of West Junggar in the western Altaids, we have conducted a combined paleomagnetic and geochronological study on Late Devonian (D3), Late Carboniferous (C2) and Early Permian (P1) successions from the Tacheng Basin, northwest of China. Both primary and secondary characteristic remanent magnetization components have been successfully isolated and yield three reliable paleomagnetic poles of C2 and Late Permian (P2) ages. The C2 and P2 poles reveal a significant clockwise rotation of 35.6°±10.4° which is comparable to the rotation deduced in the western part of the Chingiz Range during the time interval C2 to P2. Similar rotation patterns for the two units suggest that the Chingiz–West Junggar has remained as a quasi-rigid block by the P2 time and constituted the northeast limb of the Kazakhstan Orocline. The differential rotation of ca. 25° to 30° deduced between the northeast and middle limbs of the Kazakhstan Orocline further suggests that at least a part of the curvature of the Balkhash Arc was acquired during the C2 to P2 interval and was a continuation of the middle Paleozoic oroclinal bending. Moreover, the C2 poles for West Junggar and the Junggar Block are significantly different while the P2 ones almost overlap supporting the view that final closure of the Balkhash–Junggar Ocean occurred during the C2 to P2 interval. On the other hand, a large-scale counterclockwise rotation of ca. 80° to 90° is observed in West Junggar and Junggar relative to the western part of the Chingiz Range since the P2 time, and this rotation probably represents an important intra-continental deformation within the western part of the Altaids. A reconstruction of the Paleo-Asian Ocean has been proposed in which the Kazakhstan Orocline was emphasized by using the paleomagnetic results and geological evidence.

Paleomagnetism, geochronology, and magnetic mineralogy of Devonian dikes from the Kola alkaline province (NE Fennoscandian Shield)

The new paleomagnetic data on forty dikes and two intrusive plutons of Devonian age located in different parts of the Kola Peninsula, which have not been previously covered by systematic paleomagnetic studies, are reported. We describe the results of the rock magnetic, petrographic, and microprobe investigations of the Devonian dikes and present their isotopic ages (40Ar/39Ar, stepwise heating). Within the studied area, almost all the Devonian dikes, metamorphic Archaean-Proterozoic complexes of the Fennoscandian Shield, and Proterozoic dikes have undergone low-temperature hydrothermal-metasomatic alteration, which resulted in the formation of new magnetic minerals with a secondary (chemical) component of magnetization. The comparison of the paleomagnetic poles indicates the Early Jurassic age of the secondary component. We suggest that regional remagnetization event was caused by endogenic activity genetically related to the formation of the Barents Sea trap province 200–170 Ma ago. On the basis of the obtained data, the preliminary Devonian paleomagnetic pole of the East European Platform is determined.