Analysis of Strong-Field Hysteresis in High Coercivity Magnetic Minerals

2019 ◽  
pp. 127-142 ◽  
Author(s):  
A. Kosterov ◽  
E. S. Sergienko ◽  
A. G. Iosifidi ◽  
P. V. Kharitonskii ◽  
S. Yu. Yanson
Keyword(s):  
Strong Field ◽  
High Coercivity ◽  
Magnetic Minerals

High-coercivity magnetic minerals in archaeological baked clay and bricks

2020 ◽  
Vol 224 (2) ◽  
pp. 1256-1271
Author(s):  
Andrei Kosterov ◽  
Mary Kovacheva ◽  
Maria Kostadinova-Avramova ◽  
Pavel Minaev ◽  
Natalia Salnaia ◽  
...  
Keyword(s):  
Parent Material ◽  
High Coercivity ◽  
Firing Process ◽  
Magnetic Minerals ◽  
Magnetic Mineralogy ◽  
Archaeological Ceramics ◽  
Mineral Phases ◽  
Initial Magnetic Susceptibility ◽  
Magnetically Hard ◽  
Saturation Remanence

SUMMARY The thorough understanding of magnetic mineralogy is a prerequisite of any successful palaeomagnetic or archaeomagnetic study. Magnetic minerals in archaeological ceramics and baked clay may be inherited from the parent material or, more frequently, formed during the firing process. The resulting magnetic mineralogy may be complex, including ferrimagnetic phases not commonly encountered in rocks. Towards this end, we carried out a detailed rock magnetic study on a representative collection of archaeological ceramics (baked clay from combustion structures and bricks) from Bulgaria and Russia. Experiments included measurement of isothermal remanence acquisition and demagnetization as a function of temperature between 20 and >600 °C. For selected samples, low-temperature measurements of saturation remanence and initial magnetic susceptibility between 1.8 and 300 K have been carried out. All studied samples contain a magnetically soft mineral identified as maghemite probably substituted by Ti, Mn and/or Al. Stoichiometric magnetite has never been observed, as evidenced by the absence of the Verwey phase transition. In addition, one or two magnetically hard mineral phases have been detected, differing sharply in their respective unblocking temperatures. One of these unblocking between 540 and 620 °C is believed to be substituted hematite. Another phase unblocks at much lower temperatures, between 140 and 240 °C, and its magnetic properties correspond to an enigmatic high coercivity, stable, low-unblocking temperature (HCSLT) phase reported earlier. In a few samples, high- and low unblocking temperature, magnetically hard phases appear to coexist; in the others, the HCSLT phase is the only magnetically hard mineral present.

A Paleomagnetic Study of the Tectonic Deformation in Circum-Marmara Region, NW Anatolia, during the Late Cretaceous and Cenozoic Period

2020 ◽  
Author(s):  
Burak Semih Cabuk ◽  
Mualla Cengiz
Keyword(s):  
Upper Cretaceous ◽  
Rock Magnetism ◽  
Volcanic Rocks ◽  
High Coercivity ◽  
The Black Sea ◽  
Tectonic Deformation ◽  
Marmara Region ◽  
Magnetic Minerals ◽  
Single Plate ◽  
Paleomagnetic Study

<p>The Marmara region is located on the Alpine Himalayan orogenic belt which experienced a active tectonic deformation. The region consists of tectonic units such as the Istanbul Zone, the Strandja Zone and the Sakarya Continent. It is reported in the previous geological studies that the Istanbul Zone began to move southwards appart from the Moesia Platform with the effect of West Blacksea Fault in the west and West Crimea Fault in the east after the the opening of the Black Sea in the Cretaceous. It is known that the Intra Pontide suture is formed after the closure of the Intra-Pontide ocean during the Early Eocene due to the collision between İstanbulzone and the Sakarya continent which moved northwards. As a result of the continental collision, the region has completed its evolution under the influence of basin formation and the emplacement of North Anatolian Fault Zone from Miocene to the present.</p><p> </p><p>In this study, Upper Cretaceous-Oligocene sedimentary and volcanic rocks were sampled at 103 sites to investigate the tectonic deformation of the area. As a result of rock magnetism studies, it was shown that magnetic minerals in sedimentary and volcanic rocks are defined by titanium-rich titanomagnetite showing low coercivity, while in limestone samples, magnetization is defined by hematite showing high coercivity. As a result of anisotropy of magnetic susceptibility (AMS) measurements, it was observed that most of the samples show magnetic foliation and a deformation ellipsoid which is oblate. Paleomagnetic results show counterclockwise rotation of 19.9°±10.9° for the Sakarya continent, 27.4°±11.6°for the Pontides and 15.6°±11.8°for the Strandja Zone from Eocene to present. The results indicate that the region has completed the collision in Eocene and rotated counterclockwise as a large block. Deformation due to basin development or fault bounded block rotations which developed after Miocene could not been detected in this study. Miocene paleomagnetic data from previous studies in the study area are compatible with counterclockwise rotations in Upper Cretaceous-Oligocene which shows that different blocks emplaced in the study area moved together as a single plate during Eocene-Miocene time.</p>

scholarly journals Environmental control on the occurrence of high-coercivity magnetic minerals and formation of iron sulfides in a 640 ka sediment sequence from Lake Ohrid (Balkans)

2016 ◽  
Vol 13 (7) ◽  
pp. 2093-2109 ◽  
Author(s):  
Janna Just ◽  
Norbert R. Nowaczyk ◽  
Leonardo Sagnotti ◽  
Alexander Francke ◽  
Hendrik Vogel ◽  
...  
Keyword(s):  
Environmental Conditions ◽  
Environmental Control ◽  
Magnetic Mineral ◽  
High Coercivity ◽  
Water Volume ◽  
Iron Sulfides ◽  
Lake Ohrid ◽  
Magnetic Minerals ◽  
The Core ◽  
Summer Insolation

Abstract. The bulk magnetic mineral record from Lake Ohrid, spanning the past 637 kyr, reflects large-scale shifts in hydrological conditions, and, superimposed, a strong signal of environmental conditions on glacial–interglacial and millennial timescales. A shift in the formation of early diagenetic ferrimagnetic iron sulfides to siderites is observed around 320 ka. This change is probably associated with variable availability of sulfide in the pore water. We propose that sulfate concentrations were significantly higher before  ∼  320 ka, due to either a higher sulfate flux or lower dilution of lake sulfate due to a smaller water volume. Diagenetic iron minerals appear more abundant during glacials, which are generally characterized by higher Fe / Ca ratios in the sediments. While in the lower part of the core the ferrimagnetic sulfide signal overprints the primary detrital magnetic signal, the upper part of the core is dominated by variable proportions of high- to low-coercivity iron oxides. Glacial sediments are characterized by high concentration of high-coercivity magnetic minerals (hematite, goethite), which relate to enhanced erosion of soils that had formed during preceding interglacials. Superimposed on the glacial–interglacial behavior are millennial-scale oscillations in the magnetic mineral composition that parallel variations in summer insolation. Like the processes on glacial–interglacial timescales, low summer insolation and a retreat in vegetation resulted in enhanced erosion of soil material. Our study highlights that rock-magnetic studies, in concert with geochemical and sedimentological investigations, provide a multi-level contribution to environmental reconstructions, since the magnetic properties can mirror both environmental conditions on land and intra-lake processes.

scholarly journals Climatic control on the occurrence of high-coercivity magnetic minerals and preservation of greigite in a 640 ka sediment sequence from Lake Ohrid (Balkans)

2015 ◽  
Vol 12 (16) ◽  
pp. 14215-14243 ◽  
Author(s):  
J. Just ◽  
N. Nowaczyk ◽  
A. Francke ◽  
L. Sagnotti ◽  
B. Wagner
Keyword(s):  
Time Scales ◽  
Environmental Conditions ◽  
Strong Relationship ◽  
Magnetic Mineral ◽  
High Coercivity ◽  
Lake Ohrid ◽  
Magnetic Minerals ◽  
High Concentration ◽  
Magnetic Studies ◽  
Summer Insolation

Abstract. The bulk magnetic mineral record from Lake Ohrid, spanning the past ca. 640 ka, shows a strong relationship to environmental conditions on glacial–interglacial and millennial time scales. During extremely cold glacials, a lower accumulation of organic matter and likely enhanced mixing of the water-column coincides with the presence of greigite, whereas greigite is absent in sediments deposited during less severe glacials. Those "non-greigite" glacial sediments are characterized by high concentration of high-coercivity magnetic minerals, which relates to enhanced erosion of soils that had formed during the preceding interglacials. In contrast, magnetite dominated magnetic mineral assemblages characterize interglacial deposits and most likely originate from detrital particles of physically weathered rocks. Superimposed on the glacial–interglacial behavior are millennial scale oscillations in the magnetic mineral composition that parallel variations in summer insolation. Likewise to the process on glacial–interglacial time-scales, low summer insolation and a retreat in vegetation resulted in enhanced erosion of soil material. Our study highlights that rock-magnetic studies, in concert with geochemical and sedimentological investigations, provide a multi-level contribution to environmental reconstructions, since the magnetic properties can mirror both, environmental conditions on land and intra-lacustrine processes.

High-coercivity magnetic minerals in archaeological ceramics: new insights from remanence acquisition and demagnetization measurements at elevated temperatures

2020 ◽  
Author(s):  
Andrei Kosterov ◽  
Mary Kovacheva ◽  
Maria Kostadinova-Avramova ◽  
Pavel Minaev ◽  
Nataliya Sal'naya ◽  
...  
Keyword(s):  
Elevated Temperatures ◽  
Basic Research ◽  
Parent Material ◽  
High Coercivity ◽  
Firing Process ◽  
Magnetic Minerals ◽  
Magnetic Mineralogy ◽  
Archaeological Ceramics ◽  
Magnetically Hard ◽  
Basic Research Grant

<p>The thorough understanding of magnetic mineralogy is a prerequisite of any successful palaeomagnetic, and in particular, archaeomagnetic study. Magnetic minerals in archaeological ceramics and baked clay may be inherited from the parent material, or, more frequently, formed during the firing process. The resulting magnetic mineralogy may be complex, including ferrimagnetic phases not commonly encountered in rocks. Towards this end, we carried out a detailed rock magnetic study on a representative collection of archaeological ceramics (baked clay from combustion structures and bricks) from Bulgaria and Russia. Experiments included measurement of isothermal remanence acquisition and demagnetization as a function of temperature between 20°C and >600°C, and a variant of Lowrie 3-axis IRM test with measurements performed at elevated temperatures. For selected samples, low-temperature measurements of saturation remanence and initial magnetic susceptibility between 1.8 K and 300 K have been carried out.<br>All studied samples contain a magnetically soft mineral identified as maghemite probably substituted by Al and/or Ti. Stoichiometric magnetite has never been observed, as evidenced by the absence of the Verwey phase transition. In addition, one or two magnetically hard mineral phases have been detected, differing sharply in their respective unblocking temperatures. One of these unblocking between 540°C and 620°C is believed to be substituted hematite. Another phase unblocks at much lower temperatures, between 140°C and 240°C, and its magnetic properties correspond to an enigmatic high coercivity, stable?, low unblocking temperature (HCSLT) phase of McIntosh et al. [McIntosh, G., M. Kovacheva, G. Catanzariti, M. L. Osete, and L. Casas (2007), Geophys. Res. Lett., 34, L21302, doi: 10.1029/2007GL031168]. In a few samples high- and low-unblocking temperature magnetically hard phases appear to coexist, in the others the HCSLT phase is the only magnetically hard mineral present. We finally compare the samples performance in archaeointensity experiments with their respective magnetic mineralogy.<br>This study is supported by Russian Foundation of the Basic Research, grant 19-55-18006, and Bulgarian National Science Fund, grant KP-06-Russia-10.</p>

scholarly journals Rock Magnetism of Late Cretaceous to Middle Eocene Strata in the Lesser Himalaya, Western Nepal: Inferences Regarding the Paleoenvironment

2021 ◽  
Vol 9 ◽  
Author(s):  
Dhan Bahadur Khatri ◽  
Weilin Zhang ◽  
Xiaomin Fang ◽  
Qingquan Meng ◽  
Tao Zhang ◽  
...  
Keyword(s):  
Late Cretaceous ◽  
Middle Eocene ◽  
Rock Magnetism ◽  
Active Tectonics ◽  
Hysteresis Loops ◽  
High Coercivity ◽  
Lesser Himalaya ◽  
Magnetic Minerals ◽  
Tethys Sea ◽  
Sedimentary Environments

The growth of the southern piedmont of the Himalayan boundary and its depositional setting has changed since uplift of the Himalaya due to continental Indian-Eurasian collision, which has resulted in variation in magnetic minerals in marine- and terrestrial-facies sediments. In this paper, we utilize rock magnetism data from the late Cretaceous to middle Eocene strata, including the Amile and Bhainskati formations from the Lesser Himalaya (western Nepal), to understand the mechanism controlling magnetic susceptibility (χ). The active tectonics strongly influenced saturation isothermal remanent magnetization (SIRM), HIRM, and hysteresis loops, forming both low-coercivity minerals in sediments with low χ from the terrestrial facies (zones I, IIIA, and V) and high-coercivity minerals in the sediments with high χ from the marine facies (zones II, IIIB and IV). Thermomagnetic κ-T curves and frequency-dependent χ (χfd%) values show that sediments with low χ and high χ carry magnetite with coarse non-superparamagnetic (SP) grains and hematite with SP grains, respectively. Comparing the χ data with the lithologic, sedimentary environments, geomorphic features, and sea level data, we propose that low χ values were mainly produced by an increase in terrigenous detrital influx during the regression period of the Tethys Sea, while high χ values formed in marine sediments, which prompted the appearance of ferromagnetic-antiferromagnetic and paramagnetic minerals during the transgression of the Tethys Sea.

Lorentz electron microscopy of magnetic domains in rapidly solidified and annealed Pt-Co-B alloys

1991 ◽  
Vol 49 ◽  
pp. 784-785
Author(s):  
N. Qiu ◽  
J. E. Wittig
Keyword(s):  
Rapid Solidification ◽  
Ion Beam ◽  
Magnetic Behavior ◽  
High Coercivity ◽  
Magnetic Domains ◽  
Beam Angle ◽  
Tem Analysis ◽  
Intrinsic Coercivity ◽  
Hard Magnets ◽  
Rapidly Solidified

PtCo hard magnets have specialized applications owing to their relatively high coercivity combined with corrosion resistance and ductility. Increased intrinsic coercivity has been recently obtained by rapid solidification processing of PtCo alloys containing boron. After rapid solidification by double anvil splat quenching and subsequent annealing for 30 minutes at 650°C, an alloy with composition Pt42Co45B13 (at.%) exhibited intrinsic coercivity up to 14kOe. This represents a significant improvement compared to the average coercivities in conventional binary PtCo alloys of 5 to 8 kOe.Rapidly solidified specimens of Pt42Co45B13 (at.%) were annealed at 650°C and 800°C for 30 minutes. The magnetic behavior was characterized by measuring the coercive force (Hc). Samples for TEM analysis were mechanically thinned to 100 μm, dimpled to about 30 nm, and ion milled to electron transparency in a Gatan Duomill at 5 kV and 1 mA gun current. The incident ion beam angle was set at 15° and the samples were liquid nitrogen cooled during milling. These samples were analyzed with a Philips CM20T TEM/STEM operated at 200 kV.

High resolution STEM imaging study on high Tc superconductor YBa2CuaO7-x

1988 ◽  
Vol 46 ◽  
pp. 882-883
Author(s):  
H.-J. Ou ◽  
J. M. Cowley
Keyword(s):  
Crystal Structure ◽  
High Resolution ◽  
Grain Boundary ◽  
Strong Field ◽  
Imaging Study ◽  
Structure Defects ◽  
High Tc ◽  
High Tc Superconductor ◽  
Diffraction Patterns ◽  
Lattice Planes

Using the dedicate VG-HB5 STEM microscope, the crystal structure of high Tc superconductor of YBa2Cu3O7-x has been studied via high resolution STEM (HRSTEM) imaging and nanobeam (∽3A) diffraction patterns. Figure 1(a) and 2(a) illustrate the HRSTEM image taken at 10' times magnification along [001] direction and [100] direction, respectively. In figure 1(a), a grain boundary with strong field contrast is seen between two crystal regions A and B. The grain boundary appears to be parallel to a (110) plane, although it is not possible to determine [100] and [001] axes as it is in other regions which contain twin planes [3]. Following the horizontal lattice lines, from left to right across the grain boundary, a lattice bending of ∽4° is noticed. Three extra lattice planes, indicated by arrows, were found to terminate at the grain boundary and form dislocations. It is believed that due to different chemical composition, such structure defects occur during crystal growth. No bending is observed along the vertical lattice lines.

Transmission Electron Microscopy of oriented Co84Cr14Ta2 thin films for longitudinal magnetic recording

1991 ◽  
Vol 49 ◽  
pp. 756-757
Author(s):  
T. P. Nolan
Keyword(s):  
Thin Film ◽  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Low Cost ◽  
Low Noise ◽  
Information Storage ◽  
High Coercivity ◽  
Magnetic Alloy ◽  
Magnetic Media ◽  
Transmission Electron

Thin film magnetic media are being used as low cost, high density forms of information storage. The development of this technology requires the study, at the sub-micron level, of morphological, crystallographic, and magnetic properties, throughout the depth of the deposited films. As the microstructure becomes increasingly fine, widi grain sizes approaching 100Å, the unique characterization capabilities of transmission electron microscopy (TEM) have become indispensable to the analysis of such thin film magnetic media.Films were deposited at 225°C, on two NiP plated Al substrates, one polished, and one circumferentially textured with a mean roughness of 55Å. Three layers, a 750Å chromium underlayer, a 600Å layer of magnetic alloy of composition Co84Cr14Ta2, and a 300Å amorphous carbon overcoat were then sputter deposited using a dc magnetron system at a power of 1kW, in a chamber evacuated below 10-6 torr and filled to 12μm Ar pressure. The textured medium is presently used in industry owing to its high coercivity, Hc, and relatively low noise. One important feature is that the coercivity in the circumferential read/write direction is significandy higher than that in the radial direction.

RADIATIVE COLLISIONS IN A STRONG FIELD REGIME

1985 ◽  
Vol 46 (C1) ◽  
pp. C1-85-C1-95
Author(s):  
P. Pillet ◽  
R. Kachru ◽  
N. H. Tran ◽  
W. W. Smith ◽  
T. F. Gallagher
Keyword(s):  
Strong Field
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