380 research outputs found
Spin Susceptibility in the Superconducting state of Ferromagnetic Superconductor UCoGe
In order to determine the superconducting paring state in the ferromagnetic
superconductor UCoGe, ^{59}Co NMR Knight shift, which is directly related to
the microscopic spin susceptibility, was measured in the superconducting state
under magnetic fields perpendicular to spontaneous magnetization axis:
^{59}K^{a, b}. ^{59}K^{a, b} shows to be constant, but does not decrease below
a superconducting transition. These behaviors as well as the invariance of the
internal field at the Co site in the superconducting state exclude the
spin-singlet pairing, and can be interpreted with the equal-spin pairing state
with a large exchange field along the c axis, which was studied by Mineev
[Phys. Rev. B 81, 180504 (2010)].Comment: 5 pages, 4 figures, to be appear in PR
Nonreciprocal Phonon Propagation in a Metallic Chiral Magnet
The phonon magnetochiral effect (MChE) is the nonreciprocal acoustic and
thermal transports of phonons caused by the simultaneous breaking of the mirror
and time-reversal symmetries. So far, the phonon MChE has been observed only in
a ferrimagnetic insulator Cu2OSeO3, where the nonreciprocal response disappears
above the Curie temperature of 58 K. Here, we study the nonreciprocal acoustic
properties of a room-temperature ferromagnet Co9Zn9Mn2 for unveiling the phonon
MChE close to the room temperature. Surprisingly, the nonreciprocity in this
metallic compound is enhanced at higher temperatures and observed up to 250 K.
This clear contrast between insulating Cu2OSeO3 and metallic Co9Zn9Mn2 suggests
that metallic magnets have a mechanism to enhance the nonreciprocity at higher
temperatures. From the ultrasound and microwave-spectroscopy experiments, we
conclude that the magnitude of the phonon MChE of Co9Zn9Mn2 mostly depends on
the magnon bandwidth, which increases at low temperatures and hinders the
magnon-phonon hybridization. Our results suggest that the phonon nonreciprocity
could be further enhanced by engineering the magnon band of materials.Comment: 6 pages, 4 figures, 1 tabl
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
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