408 research outputs found
Metastable skyrmion lattices governed by magnetic disorder and anisotropy in -Mn-type chiral magnets
Magnetic skyrmions are vortex-like topological spin textures often observed
in structurally chiral magnets with Dzyaloshinskii-Moriya interaction. Among
them, Co-Zn-Mn alloys with a -Mn-type chiral structure host skyrmions
above room temperature. In this system, it has recently been found that
skyrmions persist over a wide temperature and magnetic field region as a
long-lived metastable state, and that the skyrmion lattice transforms from a
triangular lattice to a square one. To obtain perspective on chiral magnetism
in Co-Zn-Mn alloys and clarify how various properties related to the skyrmion
vary with the composition, we performed systematic studies on
CoZn, CoZnMn, CoZnMn and
CoZnMn in terms of magnetic susceptibility and small-angle neutron
scattering measurements. The robust metastable skyrmions with extremely long
lifetime are commonly observed in all the compounds. On the other hand,
preferred orientation of a helimagnetic propagation vector and its temperature
dependence dramatically change upon varying the Mn concentration. The
robustness of the metastable skyrmions in these materials is attributed to
topological nature of the skyrmions as affected by structural and magnetic
disorder. Magnetocrystalline anisotropy as well as magnetic disorder due to the
frustrated Mn spins play crucial roles in giving rise to the observed change in
helical states and corresponding skyrmion lattice form.Comment: 70 pages, 19 figure
Disordered skyrmion phase stabilized by magnetic frustration in a chiral magnet
Magnetic skyrmions are vortex-like topological spin textures often observed
to form a triangular-lattice skyrmion crystal in structurally chiral magnets
with Dzyaloshinskii-Moriya interaction. Recently -Mn structure-type
Co-Zn-Mn alloys were identified as a new class of chiral magnet to host such
skyrmion crystal phases, while -Mn itself is known as hosting an
elemental geometrically frustrated spin liquid. Here we report the intermediate
composition system CoZnMn to be a unique host of two disconnected,
thermal-equilibrium topological skyrmion phases; one is a conventional skyrmion
crystal phase stabilized by thermal fluctuations and restricted to exist just
below the magnetic transition temperature , and the other is a
novel three-dimensionally disordered skyrmion phase that is stable well below
. The stability of this new disordered skyrmion phase is due to a
cooperative interplay between the chiral magnetism with Dzyaloshinskii-Moriya
interaction and the frustrated magnetism inherent to -Mn.Comment: 57 pages, 16 figure
Task-adaptive physical reservoir computing
Reservoir computing is a neuromorphic architecture that may offer viable solutions to the growing energy costs of machine learning. In software-based machine learning, computing performance can be readily reconfigured to suit different computational tasks by tuning hyperparameters. This critical functionality is missing in 'physical' reservoir computing schemes that exploit nonlinear and history-dependent responses of physical systems for data processing. Here we overcome this issue with a 'task-adaptive' approach to physical reservoir computing. By leveraging a thermodynamical phase space to reconfigure key reservoir properties, we optimize computational performance across a diverse task set. We use the spin-wave spectra of the chiral magnet Cu2OSeO3 that hosts skyrmion, conical and helical magnetic phases, providing on-demand access to different computational reservoir responses. The task-adaptive approach is applicable to a wide variety of physical systems, which we show in other chiral magnets via above (and near) room-temperature demonstrations in Co8.5Zn8.5Mn3 (and FeGe)
CD4+CD56+ Lineage Negative Hematopoietic Neoplasm : So Called Blastic NK Cell Lymphoma
Blastic natural killer (NK) cell lymphoma is a rare neoplasm characterized by blastoid tumor cells expressing CD4 and CD56, with predominant skin involvement. Although this tumor has been regarded as a neoplasm related to NK cell, recent studies suggested that it is derived from plasmacytoid dendritic cells, but not from NK cell. Herein we report 4 cases of CD4+CD56+ lineage marker- blastic NK cell lymphomas with a review of literatures. The patients were 3 men and one woman. Three of them were young (17, 18, and 22 yr old). Three patients had skin lesions, at initial presentation in two patients and during the course of disease in other patient. Histologically, tumors consisted of monotonous medium to large blastoid cells showing no necrosis, angiocentric growth or epidermotrophism. All four tumors were CD4+ and CD56+. Three expressed CD68 antigen. Lineage specific markers for B- and T cell were negative. All tumors did not express myeloperoxidase. T-cell receptor gene rearrangement, EBV, CD13 and CD33 were negative. In one patient, tumor cells arranged in Homer-Wright type pseudorosette and expressed terminal deoxynucleotidyl transferase (TdT). Despite the standard lymphoma chemotherapy, the tumors, except one lost during follow-up, progressed and relapsed. The patients died 8-60 months after diagnosis
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