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Jinho Kim - One of the best experts on this subject based on the ideXlab platform.

  • induced versus intrinsic magnetic moments in ultrafast magnetization dynamics
    Physical Review B, 2018
    Co-Authors: Moritz Hofherr, Simone Moretti, J H Shim, S Hauser, N Y Safonova, M Stiehl, A Ali, S Sakshath, Jinho Kim
    Abstract:

    One of the ultimate goals for future spintronic applications is to manipulate magnetic states of matter on the shortest of timescales. Here, the authors investigate the optically induced ultrafast Demagnetization and remagnetization dynamics of ferromagnetic alloys based on either intrinsic or induced magnetic moments. Using pump-probe spectroscopy in combination with dynamic spin model simulations, they find that a CoFeB alloy with intrinsic magnetic moments on the Fe and Co sites reveals a distinct asymptotic amplitude limit of the remagnetization process, while in FePt the induced moments of the Pt sites stay always proportional to those of Fe.

Ju Lee - One of the best experts on this subject based on the ideXlab platform.

  • Demagnetization analysis of permanent magnets according to rotor types of interior permanent magnet synchronous motor
    IEEE Transactions on Magnetics, 2009
    Co-Authors: Kichan Kim, Kwangsoo Kim, Heejun Kim, Ju Lee
    Abstract:

    This paper shows a study on the Demagnetization performance analysis of permanent magnet according to three kinds of rotor types of an interior permanent magnet synchronous motor (IPMSM). It is very important to consider Demagnetization performance as well as motor performance such as rated torque, output current, and efficiency when designing IPMSM. Three kinds of rotor types according to permanent magnet arrangement; single layer type, v shape type, and double layer type are generally used for IPMSM. In the paper, the magnetic equivalent circuits according to each rotor type are proposed in order for initial design of thickness of permanent magnets considering Demagnetization by lumped constant related to magnetic circuit. The volume of permanent magnets per pole and back EMF of each rotor type is assumed to equal for the comparison of Demagnetization of IPMSMs with same performance each other. Next, distribution of Demagnetization in the permanent magnet is analyzed by using finite element method (FEM) for the verification of the results by magnetic equivalent circuit.

  • the shape design of permanent magnet for permanent magnet synchronous motor considering partial Demagnetization
    IEEE Transactions on Magnetics, 2006
    Co-Authors: Kichan Kim, Seungbin Lim, Daehyun Koo, Ju Lee
    Abstract:

    This paper presents a study on shape design of permanent magnets that is focused on robustness for cogging torque, sinusoidal back emf, and partial Demagnetization of the permanent magnet of the outer rotor permanent magnet synchronous motor (PMSM). The simulation method for partial Demagnetization is proposed and performed with four kinds of permanent magnet shape models at the fault current and two kinds of load angles corresponding to maximum torque operation and short circuit operation by finite-element method (FEM). The robust shape model of permanent magnets for large-sized hybrid electric vehicles is presented. The characteristics after partial Demagnetization are analyzed and compared with experimental results for verification of the partial Demagnetization effect

  • effect of design variables on irreversible permanent magnet Demagnetization in flux reversal machine
    International Conference on Electrical Machines and Systems, 2005
    Co-Authors: Tae Heoung Kim, Seungkil Choi, Cheoljick Ree, Ju Lee
    Abstract:

    The large demagnetizing currents in flux-reversal machine (FRM) are generated by the short-circuited of stator windings and the fault of a drive circuit. So, irreversible magnet Demagnetization occurs due to the external demagnetizing field by these currents. In this paper, we deal with the effect of design variables on irreversible magnet Demagnetization in the FRM using two-dimensional finite-element method (2D FEM). The nonlinear analysis of a permanent magnet is added to 2D FEM to consider irreversible Demagnetization. As a result, it is shown that magnet thickness and rotor teeth width are the most important geometrical dimensions of the FRM in terms of irreversible magnet Demagnetization.

  • effect of design variables on irreversible magnet Demagnetization in brushless dc motor
    Journal of Applied Physics, 2005
    Co-Authors: Tae Heoung Kim, Ju Lee
    Abstract:

    The large demagnetizing currents in brushless dc (BLdc) motor are generated by the short-circuited stator windings and the fault of a drive circuit. So, irreversible magnet Demagnetization occurs due to the external demagnetizing field by these currents. In this paper, we deal with the effect of design variables on irreversible magnet Demagnetization in BLdc motor through the modeling approach using a two-dimensional finite-element method (2D FEM). The nonlinear analysis of a permanent magnet is added to 2D FEM to consider irreversible Demagnetization. As a result, it is shown that magnet thickness, teeth surface width, and rotor back yoke thickness are the most important geometrical dimensions of BLdc motor in terms of irreversible magnet Demagnetization.

Moritz Hofherr - One of the best experts on this subject based on the ideXlab platform.

  • induced versus intrinsic magnetic moments in ultrafast magnetization dynamics
    Physical Review B, 2018
    Co-Authors: Moritz Hofherr, Simone Moretti, J H Shim, S Hauser, N Y Safonova, M Stiehl, A Ali, S Sakshath, Jinho Kim
    Abstract:

    One of the ultimate goals for future spintronic applications is to manipulate magnetic states of matter on the shortest of timescales. Here, the authors investigate the optically induced ultrafast Demagnetization and remagnetization dynamics of ferromagnetic alloys based on either intrinsic or induced magnetic moments. Using pump-probe spectroscopy in combination with dynamic spin model simulations, they find that a CoFeB alloy with intrinsic magnetic moments on the Fe and Co sites reveals a distinct asymptotic amplitude limit of the remagnetization process, while in FePt the induced moments of the Pt sites stay always proportional to those of Fe.

R S Middleton - One of the best experts on this subject based on the ideXlab platform.

  • remagnetization 1100ma of voosges lake tuff 1542ma and other mid proterozoic rocks nipigon graben northern ontario
    Precambrian Research, 2008
    Co-Authors: Graham J. Borradaile, Donald W Davis, R S Middleton, I Geneviciene
    Abstract:

    Abstract Recently discovered horizons of non-deformed felsic welded crystal tuff in the Proterozoic rift system of northern Ontario yield a geologically stable paleomagnetic vector. Using alternating field (AF), thermal (TD) and low-temperature Demagnetization (LTD) techniques, a single stable characteristic remanence (ChRM) vector is found in all specimens (declination/inclination = 115°/−73.5°; α95 = 2.1°, n = 58). It is overprinted by a Bruhnes’ epoch VRM. The tuffs paleopole position coincides with that of ubiquitous sub-horizontal diabase sheets which intruded at ∼1110 Ma during Late Proterozoic Keewanawan Volcanism. The latter produced numerous volcanic and intrusive rocks along the margins of the Lake Superior paleo-rift system, during the interval 1087–1120 Ma, but the sills are most extensive. Although the Voosges Lake Tuff shares the same paleopole location as the diabase sheets (1109 Ma), the nearby Seagull pluton (1112 Ma) and the Keweenawan volcanic rocks, its primary zircons yielded a Mesoproterozoic crystallization age of 1542 ± 3 Ma. This is similar to the nearby English Bay felsic intrusions dated at 1537 − 2 + 10 Ma [Davis, D.W., Sutcliffe, R.H., 1985. U-Pb ages from the Nipigon “Plate” (sic) and northern Lake Superior. Geol. Soc. Am. Bull. 96, 1572–1579]. Whereas the paleomagnetic magnetic signal appears primary in the 1542 Ma Voosges Tuff, it was completely reset by the Late Proterozoic Keewanawan paleofield (∼1100 Ma). The Tuff units are separated from the diabase sills by stratigraphic thicknesses of ≤50 m and show no traditional petrographic evidence of annealing or thermal metamorphism. Since it is improbable that the 1542 Ma tuff returned to the same paleolatitude at 1109 Ma, we postulate that metasomatic processes caused a ∼1109 Ma remagnetization. A similar event could explain unusual ChRMs reported for certain other pre-Keweenawan Proterozoic sites with adjacent Keewanawan diabase sheets. For example, some paleopoles reported for the Gunflint Formation (1878 Ma) and Sibley Formation (>1339 Ma, perhaps ∼1537 Ma by association with the English Bay intrusions) might have been acquired due to secondary remagnetization.

  • low temperature Demagnetization isolates stable magnetic vector components in magnetite bearing diabase
    Geophysical Journal International, 2004
    Co-Authors: Graham J. Borradaile, K Lucas, R S Middleton
    Abstract:

    SUMMARY It may be difficult to isolate stable palaeomagnetic vectors of different ages if they lie in grain assemblages with overlapping ranges of coercivity or of unblocking temperature. This is because some moments associated with either vector may demagnetize at the same stage of experimental Demagnetization. The sharp transition between vector components may be obscured and stable components may appear less linear on the Demagnetization plot. Thermal and alternating field (AF) Demagnetization techniques remove vector components on a quantitative basis, according to a discrete limiting unblocking temperature or coercivity. Low-temperature Demagnetization (LTD) differs in that it removes vector components discretely, wherever there are mobile domain walls. Experiments tested the ability of LTD to improve the effectiveness of AF Demagnetization on isothermal and anhysteretic remanent magnetizations (IRM, ARM) in diabase. Multicomponent NRMs were simulated IRMs or ARMs in different, non-overlapping coercivity ranges, along three orthogonal axes or along two non-orthogonal directions. The known directions of the experimentally applied vector components were always more successfully verified by AF Demagnetization if LTD was first applied. For the same specimens, LTD reduced the same artificial remanences by ∼50 per cent for the coercivity range 0–15 mT, by ∼25 per cent for the range 15–30 mT, and negligibly for higher-coercivity fractions. LTD demagnetizes polydomain magnetite as domain walls rearrange on passing through a low-temperature transition, near 120 K.

  • proterozoic diabase sills of northern ontario magnetic properties and history
    Journal of Geophysical Research, 2004
    Co-Authors: R S Middleton, Graham J. Borradaile, D Baker, K Lucas
    Abstract:

    [1] Magnetic fabrics show that a series of massive diabase sills (“Logan sills”) possess flow fabrics away from the midcontinental Proterozoic rift system, near its triple junction on the north shore of Lake Superior. Their intense remanences are commonly antiparallel to the geomagnetic field, requiring some knowledge of natural remanent magnetization in order to interpret of ground magnetic surveys. Thermal Demagnetization, low-temperature Demagnetization, and the combined techniques yield differently oriented characteristic remanence vectors in some of these sills. Although the commonly reported “Keweenawan” reversed paleofield direction is verified by most A components, the orientation of vectors within sites and through the thickness of sills is large and may be attributed to reversals, excursions, and secular variation. B components are mostly down, but their orientation distribution is poorly concentrated. Low-temperature Demagnetization, prior to thermal Demagnetization, tends to improve the consistency of vectors defined in subsequent thermal Demagnetization. Moreover, in some cases, three to five cycles of low-temperature Demagnetization alone produces the same result as the more time-consuming thermal Demagnetization. Some within-site scatter of the A components is large, and some anomalous specimen directions and alternate polarities may be associated with platinum group mineralization. Whereas the grand mean direction for all sites lies on the available apparent polar wander path between 1100 and 1300 Ma, the mean paleopole locations differ at the 95% level for different Demagnetization treatments of specimens from the same sites.

N Y Safonova - One of the best experts on this subject based on the ideXlab platform.

  • induced versus intrinsic magnetic moments in ultrafast magnetization dynamics
    Physical Review B, 2018
    Co-Authors: Moritz Hofherr, Simone Moretti, J H Shim, S Hauser, N Y Safonova, M Stiehl, A Ali, S Sakshath, Jinho Kim
    Abstract:

    One of the ultimate goals for future spintronic applications is to manipulate magnetic states of matter on the shortest of timescales. Here, the authors investigate the optically induced ultrafast Demagnetization and remagnetization dynamics of ferromagnetic alloys based on either intrinsic or induced magnetic moments. Using pump-probe spectroscopy in combination with dynamic spin model simulations, they find that a CoFeB alloy with intrinsic magnetic moments on the Fe and Co sites reveals a distinct asymptotic amplitude limit of the remagnetization process, while in FePt the induced moments of the Pt sites stay always proportional to those of Fe.