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Jong-ryul Jeong - One of the best experts on this subject based on the ideXlab platform.
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Ultrafast giant magnetic cooling effect in ferromagnetic Co/Pt multilayers
Nature Communications, 2017Co-Authors: Je-ho Shim, Akbar Ali Syed, Seung-young Park, Jong-ryul JeongAbstract:The magnetic cooling effect originates from a large change in entropy by the forced magnetization alignment, which has long been considered to be utilized as an alternative environment-friendly cooling technology compared to conventional refrigeration. However, an ultimate timescale of the magnetic cooling effect has never been studied yet. Here, we report that a giant magnetic cooling (up to 200 K) phenomenon exists in the Co/Pt nano-multilayers on a femtosecond timescale during the photoinduced demagnetization and Remagnetization, where the disordered spins are more rapidly aligned, and thus magnetically cooled, by the external magnetic field via the lattice-spin interaction in the multilayer system. These findings were obtained by the extensive analysis of time-resolved magneto-optical responses with systematic variation of laser fluence as well as external field strength and direction. Ultrafast giant magnetic cooling observed in the present study can enable a new avenue to the realization of ultrafast magnetic devices. The forced alignment of magnetic moments leads to a large change in entropy, which can be used to reduce the temperature of a material. Here, the authors show that this magnetic cooling effect occurs on a femtosecond time scale in cobalt–platinum nano-multilayers.
Je-ho Shim - One of the best experts on this subject based on the ideXlab platform.
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Direct Observation of Terahertz Emission from Ultrafast Spin Dynamics in Thick Ferromagnetic Films
AMER INST PHYSICS, 2019Co-Authors: Kim, Dong Eon, Huang L., Kim Ji-wan, Lee, Sang Hyuk, Kim, Seon Dae, Tien,van Manh, Shinde, Kiran Prakash, Je-ho Shim, Shin Yooleemi, Shin, Hee JunAbstract:We have experimentally investigated the field- and fluence-dependent terahertz (THz) emission behaviors by a femtosecond optical pump in Co ferromagnetic films, together with the time-resolved magneto-optical Kerr effect measurement. The thickness of Co and Ta capping layers has been systematically varied. For thick films, THz emission behavior is found to be directly matched with the photoinduced ultrafast demagnetization and Remagnetization dynamics. The angle-dependent THz emission measurement also confirms a direct relation between the THz emission and the photoinduced demagnetization/Remagnetization dynamics in the case of thick films, while THz emission from the inverse spin Hall effect also plays a role in the case of thin Co films.1
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Intriguing Hysteresis Dynamics in Ultrafast Photo-Induced Magnetization
WILEY-V C H VERLAG GMBH, 2019Co-Authors: Je-ho Shim, Kim, Dong Eon, Kim Chul-hoon, Piao Hong-guang, Lee Sang-hyuk, Lee, Kyung Min, Jeong Jong-ryul, Park Seung-young, Choi, Yeon Suk, Kim Dong-hyunAbstract:Time-resolved magneto-optical Kerr effect measurement is carried out to determine ultrafast hysteresis behavior during a photo-induced demagnetization/Remagnetization process for Co/Pt ferromagnetic multilayers. Due to the stroboscopic measurement scheme, hysteresis curve measured by a pump-probe technique exhibits an irreversible behavior, repeatedly reset to a metastable hysteresis state at each stroboscopic measurement, observed as the reduction of the coercivity. It is demonstrated that the stroboscopically measured hysteresis and the coercivity could be a stable parameter in describing the ultrafast photo-induced spin dynamics for both reversible and irreversible behaviors. Moreover, it is found that an unusual coercivity behavior exists together with a nontrivial magnetization change under external fields comparable to the coercivity of the sample.1
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Ultrafast giant magnetic cooling effect in ferromagnetic Co/Pt multilayers
Nature Publishing Group, 2019Co-Authors: Je-ho Shim, Kim Chul-hoon, Lee, Kyung Min, Jeong Jong-ryul, Park Seung-young, Kim Dong-hyun, Syed, Akbar Ali, Kim, Dong EonAbstract:The magnetic cooling effect originates from a large change in entropy by the forced magnetization alignment, which has long been considered to be utilized as an alternative environment-friendly cooling technology compared to conventional refrigeration. However, an ultimate timescale of the magnetic cooling effect has never been studied yet. Here, we report that a giant magnetic cooling (up to 200 K) phenomenon exists in the Co/Pt nanomultilayers on a femtosecond timescale during the photoinduced demagnetization and Remagnetization, where the disordered spins are more rapidly aligned, and thus magnetically cooled, by the external magnetic field via the lattice-spin interaction in the multilayer system. These findings were obtained by the extensive analysis of time-resolved magneto-optical responses with systematic variation of laser fluence as well as external field strength and direction. Ultrafast giant magnetic cooling observed in the present study can enable a new avenue to the realization of ultrafast magnetic devices.11
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Ultrafast giant magnetic cooling effect in ferromagnetic Co/Pt multilayers
Nature Communications, 2017Co-Authors: Je-ho Shim, Akbar Ali Syed, Seung-young Park, Jong-ryul JeongAbstract:The magnetic cooling effect originates from a large change in entropy by the forced magnetization alignment, which has long been considered to be utilized as an alternative environment-friendly cooling technology compared to conventional refrigeration. However, an ultimate timescale of the magnetic cooling effect has never been studied yet. Here, we report that a giant magnetic cooling (up to 200 K) phenomenon exists in the Co/Pt nano-multilayers on a femtosecond timescale during the photoinduced demagnetization and Remagnetization, where the disordered spins are more rapidly aligned, and thus magnetically cooled, by the external magnetic field via the lattice-spin interaction in the multilayer system. These findings were obtained by the extensive analysis of time-resolved magneto-optical responses with systematic variation of laser fluence as well as external field strength and direction. Ultrafast giant magnetic cooling observed in the present study can enable a new avenue to the realization of ultrafast magnetic devices. The forced alignment of magnetic moments leads to a large change in entropy, which can be used to reduce the temperature of a material. Here, the authors show that this magnetic cooling effect occurs on a femtosecond time scale in cobalt–platinum nano-multilayers.
Rob Van Der Voo - One of the best experts on this subject based on the ideXlab platform.
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Concurrence of folding and Remagnetization events in the Monterrey Salient (NE Mexico)
Tectonophysics, 2019Co-Authors: Samantha R. Nemkin, Elisa Fitz-díaz, Ben A. Van Der Pluijm, Gabriel Chávez-cabello, Rob Van Der VooAbstract:Abstract Carbonate formations from many locations reveal magnetizations that are secondary. Attaching a numerical age to these Remagnetizations would provide information on orogenic processes. To contribute to the effort of assigning an age to Remagnetization events, Lower Cretaceous formations from the Monterrey Salient in northeast Mexico were sampled. Individual fold tests reveal eight site-pair synfolding Remagnetizations (set A) of Eocene age. The remanence is a chemical remanent magnetization (CRM) carried by magnetite. The magnetization of set B is possibly due to an early carbonate alteration that produced a remanence significantly older than folding. A complexity of set B is that the site pairs reveal k-versus-unfolding percentage diagrams with maximum unfolding peaks at 100 to 125%. An explanation of multiple deformation phases with an earlier horizontal folding phase around a non-plunging horizontal axis and a later vertical axis rotation is suggested for the past 100% peaks of the B sites. The latter deformation, rotation about a vertical axes, is revealed by a declination-strike test in set A sites and site means of the full collection that deviate counterclockwise from the reference declination. By combining synfolding results with published 40Ar/39Ar illite ages of folding (Fitz-Diaz et al., 2016), Remagnetization ages in set A sites of 48–52 Ma are obtained. The magnetization in set B sites is likely older, though not well constrained. Interestingly, prior results from the central Sierra Madre Oriental, to the south, show two Remagnetization events, Late Cretaceous and Early Eocene in age, in a succession from W to E (Nemkin et al., 2015). The age of folding and Remagnetization acquisition in set A sites along the Monterrey Salient are concurrent with the frontal, remagnetized folds in the central Sierra Madre Oriental. Thus, the timing of major Remagnetization in the Monterrey Salient occurred in the Eocene.
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Remagnetization and folding in the frontal Montana Rocky Mountains
Lithosphere, 2016Co-Authors: Samantha R. Nemkin, Ben A. Van Der Pluijm, David R. Lageson, Rob Van Der VooAbstract:Local-scale folds within the Mississippian Madison Group of the frontal Montana Rockies preserve pre- and synfolding Remagnetization data. Paleomagnetic results display inclinations of ∼70°, in contrast to the expected shallower directions for North American Mississippian rocks. The magnetization is chemical in origin, preserved in superparamagnetic to single-domain magnetite grains from fluid activity. Magnetic intensity results in the study area suggest that mineralization was more prevalent in the interior of the fold-and-thrust belt and diminished toward the east, resulting in lower intensities from less magnetite growth in the very frontal portions of the belt into the foreland. Fold test results of individual folds show syn- and prefolding Remagnetizations as a function of location across the belt, with synfolding results in more westerly locations and prefolding results in the most frontal folds of the belt. By comparing our synfolding results with previously determined deformation ages for the Rocky Mountains, an Eocene (53.6 Ma) age for the Remagnetization can be assigned. Based on the relative timing of Remagnetization, a spatial pattern of folding in the study area is revealed. Major folding commenced (i.e., synfolding magnetization) during an Eocene Remagnetization event, while the most frontal portion remained undeformed (i.e., prefolding magnetization) and was subsequently folded after regional Remagnetization.
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Dating synfolding Remagnetization: Approach and field application (central Sierra Madre Oriental, Mexico)
Geosphere, 2015Co-Authors: Samantha R. Nemkin, Elisa Fitz-díaz, Ben A. Van Der Pluijm, Rob Van Der VooAbstract:Growth of magnetite has been variably linked to fluid-bearing events or clay diagenesis, and the development of a chemical Remagnetization as a result of such events. In this study we examine remagnetized carbonate rocks from the central Sierra Madre Oriental (the Mexican fold-thrust belt) in order to develop a method for dating synfolding Remagnetizations. By combining 40 Ar/ 39 Ar deformation ages with new paleomagnetic results, we present a quantitative method for absolute dating of synfolding Remagnetization. We find that the history of the central Sierra Madre Oriental involved two separate Remagnetization events in our study area; synfolding remanence acquisition ca. 77 Ma (Late Cretaceous) in the Zimapan Basin and a younger synfolding Remagnetization event ca. 44 Ma (mid-Eocene) in the Tampico-Misantla Basin. The growth of magnetite leading to chemical Remagnetization detected in these limestones is interpreted as the result of rock interactions with an Fe-bearing fluid.
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Remagnetization in the Tennessee salient, Southern Appalachians, USA: Constraints on the timing of deformation
Tectonophysics, 2009Co-Authors: James S. Hnat, Ben A. Van Der Pluijm, Rob Van Der VooAbstract:article i nfo The Appalachian fold-thrust belt is characterized by a sinuous trace in map-view, creating a series of salients and recesses. The kinematic evolution of these arcuate features remains a controversial topic in orogenesis. Primary magnetizations from clastic red beds in the Pennsylvania salient show Pennsylvanian rotations that account for about half of the curvature, while Kiaman-aged (Permian) Remagnetizations display no relative rotation between the limbs. The more southern Tennessee salient shows a maximum change in regional strike from ~65° in Virginia to ~10° in northern Georgia. Paleomagnetic results from thirty-two sites in the Middle to Upper Ordovician Chickamauga Group limestones and twenty sites from the Middle Cambrian Rome Formation red beds were analyzed to constrain the relative age of magnetization as well as the nature of curvature in the Tennessee salient. Results from three sites of the Silurian Red Mountain Formation were added to an existing dataset in order to determine whether the southern limb had rotated. After thermal demagnetization, all three sample suites display a down and southeasterly direction, albeit carried by different magnetic minerals. The syn-tilting direction of the Chickamauga limestones lies on the Pennsylvanian segment of the North American apparent polar wander path (APWP), indicating that deformation was about half completed by the Late Pennsylvanian. The Rome and Red Mountain Formations were also remagnetized during the Pennsylvanian. Both the Chickamauga limestones and Rome red beds fail to show a correlation between strike and declination along the salient, suggesting either that the salient was a primary, non-rotational feature or that secondary curvature occurred prior to Remagnetization, as it did in Pennsylvania. Moreover, remagnetized directions from the Red Mountain sites show no statistical difference between the southern limb of the salient and the more northeasterly trending portion of the fold-thrust belt in Alabama. Thus, all of the studied units in the Tennessee salient are remagnetized and show no evidence for rotation. This confirms that Remagnetization was widespread in the southern Appalachians and that any
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insights into the mechanism for orogen related carbonate Remagnetization from growth of authigenic fe oxide a scanning electron microscopy and rock magnetic study of devonian carbonates from northern spain
Journal of Geophysical Research, 2002Co-Authors: Arlo Brandon Weil, Rob Van Der VooAbstract:[1] A rock magnetic and SEM study of Devonian carbonates from the Cantabria-Asturias Region, northern Spain, was undertaken to further our understanding of the pervasive Remagnetization of carbonate rocks during the Late Paleozoic, and the mechanism by which these Remagnetizations occur. These rocks contain three ancient Late Paleozoic magnetizations. The rock magnetic properties of mineral extracts were compared with those of whole rock chips and “nonmagnetic” residue to deduce magnetic carrier(s) and grain sizes. Hysteresis measurements for rock chips show “typical” wasp-waisted loops, whereas extract shows typical pseudosingle-domain-like (PSD) unrestricted loops. Within all sites, there is a noticeable contribution of superparamagnetic (SP) grains seen in hysteresis properties and low-temperature magnetization measurements of whole rock chips, whereas a trend away from a strong SP contribution is seen when hysteresis properties of whole rock are compared with those of residue and extract. Consequently, our extraction process (predictably) removes SP grains, while preserving the characteristic fraction of remanence-carrying material, which behaves like a typical mixture of single-domain (SD) and PSD magnetite. Paradoxically, the typical “fingerprint” of remagnetized carbonates, as seen in the whole rock data, seems to be a response to abundant SP grains associated with the acquisition of chemical remanent magnetizations (CRM), and not the actual remanence carrying population itself. Scanning electron microscopy (SEM) observations of magnetic extract reveal abundant authigenic Fe-oxides, characterized as either 10–100 μm Ni-free spherules or individual 0.1–10 μm euhedral grains. SEM observations of thin sections reveal abundant evidence of fluid flow driven chemical reactions that resulted in formation of new Fe oxide. Such reactions occurred along cracks and grain boundaries and within void space, and are associated with Fe-rich clay and calcite-dolomite reactions or as oxidation of Fe-sulfide framboids. Together, the SEM observations and rock magnetic experiments reveal that the three Late Paleozoic Remagnetizations experienced by Cantabria-Asturias Paleozoic carbonates are CRMs facilitated by the presence of fluids activated during Late Paleozoic Variscan deformation.
Guillaume Dupont-nivet - One of the best experts on this subject based on the ideXlab platform.
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Challenges in isolating primary remanent magnetization from Tethyan carbonate rocks on the Tibetan Plateau: Insight from remagnetized Upper Triassic limestones in the eastern Qiangtang block
Earth and Planetary Science Letters, 2019Co-Authors: Wentao Huang, Michael Jackson, Mark Dekkers, Yang Zhang, Bo Zhang, Zhaojie Guo, Guillaume Dupont-nivetAbstract:Carbonate rocks, widely used for paleomagnetically quantifying the drift history of the Gondwana-derived continental blocks of the Tibetan Plateau and evolution of the Paleo/Meso/Neo-Tethys Oceans, are prone to pervasive Remagnetization. Identifying Remagnetization is difficult because it is commonly undetectable through the classic paleomagnetic field tests. Here we apply comprehensive paleomagnetic, rock magnetic, and petrographic studies to upper Triassic limestones in the eastern Qiangtang block. Our results reveal that detrital/biogenic magnetite, which may carry the primary natural remanent magnetization (NRM), is rarely preserved in these rocks. In contrast, authigenic magnetite and hematite pseudomorphs after pyrite, and monoclinic pyrrhotite record three episodes of Remagnetization. The earliest Remagnetization was induced by oxidation of early diagenetic pyrite to magnetite, probably related to the collision between the northeastern Tibetan Plateau and the Qiangtang block after closure of the Paleo-Tethys Ocean in the Late Triassic. The second Remagnetization, residing in hematite and minor goethite, which is the further subsurface oxidation product of pyrite/magnetite, is possibly related to the development of the localized Cenozoic basins soon after India-Asia collision in the Paleocene. The youngest Remagnetization is a combination of thermoviscous and chemical remanent magnetization carried by authigenic magnetite and pyrrhotite, respectively. Our analyses suggest that a high supply of organic carbon during carbonate deposition, prevailing sulfate reducing conditions during early diagenesis, and widespread orogenic fluid migration related to crustal shortening during later diagenesis, have altered the primary remanence of the shallow-water Tethyan carbonate rocks of the Tibetan Plateau. We emphasize that all paleomagnetic results from these rocks must be carefully examined for Remagnetization before being used for paleogeographic reconstructions. Future paleomagnetic investigations of the carbonate rocks in orogenic belts should be accompanied by thorough rock magnetic and petrographic studies to determine the origin of the NRM.
L Jahn - One of the best experts on this subject based on the ideXlab platform.
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Thermal Remagnetization in Polycrystalline Permanent Magnets
arXiv: Materials Science, 2003Co-Authors: R Schumann, L JahnAbstract:The thermal Remagnetization (TR), i.e. the reentrance of magnetization upon heating in a steady-field demagnetized sample, is a common feature to the four types of polycrystalline permanent magnets, mainly utilized for practical purposes, i.e. barium ferrites, SmCo5, Sm2Co17 and NdFeB magnets. The effect is small for pinning controlled and large for nucleation controlled magnets. The effect is strongly dependent on the demagnetization factor and may reach nearly 100 per cent in SmCo5 samples measured in a closed circuit. The TR is very sensitive to a small superimposed steady field. The maximum effect and the position of the peak is dependent on the initial temperature. The direction of the TR is correlated with the temperature coefficient of the coercivity, resulting in a inverse TR in barium ferrite. The susceptibility of the thermally remagnetized samples is increased. Repeated cycles of steady-field demagnetization followed by heating result in the same TR. The phenomenology of TR and ITR is explained by means of a model taking into account both the internal field fluctuations due to grain interactions and the decay of single domain grains into multi-domain state. By taking the measured temperature dependencies of the coercivity and the saturation magnetization the theory is able to reproduce the experiments very well, allowing to determine the width of the field fluctuations, the width of the switching field distribution and an internal demagnetization factor as characteristics of the materials by fitting.
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theory of thermal Remagnetization of permanent magnets
Journal of Magnetism and Magnetic Materials, 2001Co-Authors: R Schumann, L JahnAbstract:Abstract A self-consistent mean-field theory explaining the thermal Remagnetization (TR) of polycrystalline permanent magnets is given. The influence of the environment of a grain is treated by an inclusion approximation, relating the field inside the grain to the local field outside by means of an internal demagnetization factor n . For the switching fields and the fluctuations of the local fields around the mean field, Gaussian distributions of widths σ s , and σ f , respectively, are assumed. The isothermal hysteresis curve, the recoil curves, and the TR dependent on the model parameters n , σ s , and σ f are calculated. Furthermore, the influence of the initial temperature and the strong dependence of the TR on the demagnetization factor of the sample are studied, and it is shown that for reasonable parameter sets TR effects up to 100% are possible. The theoretical results correspond well with the experimental situation.