23 research outputs found
Pressure-induced huge increase of Curie temperature of the van der Waals ferromagnet VI3
Evolution of magnetism in single crystals of the van der Waals compound VI3
in external pressure up to 7.3 GPa studied by measuring magnetization and ac
magnetic susceptibility is reported. Four magnetic phase transitions, at T1 =
54.5 K, T2 = 53 K, TC = 49.5 K, and TFM = 26 K, respectively have been observed
at ambient pressure. The first two have been attributed to the onset of
ferromagnetism in specific crystal-surface layers. The bulk ferromagnetism is
characterized by the magnetic ordering transition at Curie temperature TC and
the transition between two different ferromagnetic phases TFM, accompanied by a
structure transition from monoclinic to triclinic symmetry upon cooling. The
pressure effects on magnetic parameters were studied with three independent
techniques. TC was found to be almost unaffected by pressures up to 0.6 GPa
whereas TFM increases rapidly with increasing pressure and reaches TC at a
triple point at ~ 0.85 GPa. At higher pressures, only one magnetic phase
transition is observed moving to higher temperatures with increasing pressure
to reach 99 K at 7.3 GPa. In contrast, the low-temperature bulk magnetization
is dramatically reduced by applying pressure (by more than 50% at 2.5 GPa)
suggesting a possible pressure-induced reduction of vanadium magnetic moment.
We discussed these results in light of recent theoretical studies to analyze
exchange interactions and provide how to increase the Curie temperature of VI3.Comment: 20 pages, 16 figure
Electric Quadrupolar Contributions in the Magnetic Phases of UNiB
We present acoustic signatures of the electric quadrupolar degrees of freedom
in the honeycomb-layer compound UNiB. The transverse ultrasonic mode
shows softening below 30 K both in the paramagnetic phase and
antiferromagnetic phases down to K. Furthermore, we traced magnetic
field-temperature phase diagrams up to 30 T and observed a highly anisotropic
elastic response within the honeycomb layer. These observations strongly
suggest that (E) electric quadrupolar degrees of freedom
in localized () states are playing an important role in the
magnetic toroidal dipole order and magnetic-field-induced phases of UNiB,
and evidence some of the U ions remain in the paramagnetic state even if the
system undergoes magnetic toroidal ordering.Comment: 6 pages, 4 figures + Supplemental Materials (11 pages, 9 figures
Band structure of CuMnAs probed by optical and photoemission spectroscopy
The tetragonal phase of CuMnAs progressively appears as one of the key materials for antiferromagnetic spintronics due to efficient current-induced spin-torques whose existence can be directly inferred from crystal symmetry. Theoretical understanding of spintronic phenomena in this material, however, relies on the detailed knowledge of electronic structure (band structure and corresponding wave functions) which has so far been tested only to a limited extent. We show that AC permittivity (obtained from ellipsometry) and UV photoelectron spectra agree with density functional calculations. Together with the x-ray diffraction and precession electron diffraction tomography, our analysis confirms recent theoretical claim [Phys. Rev. B 96, 094406 (2017)] that copper atoms occupy lattice positions in the basal plane of the tetragonal unit cell
Altermagnetic lifting of Kramers spin degeneracy
Lifted Kramers spin-degeneracy has been among the central topics of
condensed-matter physics since the dawn of the band theory of solids. It
underpins established practical applications as well as current frontier
research, ranging from magnetic-memory technology to topological quantum
matter. Traditionally, lifted Kramers spin-degeneracy has been considered to
originate from two possible internal symmetry-breaking mechanisms. The first
one refers to time-reversal symmetry breaking by magnetization of ferromagnets,
and tends to be strong due to the non-relativistic exchange-coupling origin.
The second mechanism applies to crystals with broken inversion symmetry, and
tends to be comparatively weaker as it originates from the relativistic
spin-orbit coupling. A recent theory work based on spin-symmetry classification
has identified an unconventional magnetic phase, dubbed altermagnetic, that
allows for lifting the Kramers spin degeneracy without net magnetization and
inversion-symmetry breaking. Here we provide the confirmation using
photoemission spectroscopy and ab initio calculations. We identify two distinct
unconventional mechanisms of lifted Kramers spin degeneracy generated by the
altermagnetic phase of centrosymmetric MnTe with vanishing net magnetization.
Our observation of the altermagnetic lifting of the Kramers spin degeneracy can
have broad consequences in magnetism. It motivates exploration and exploitation
of the unconventional nature of this magnetic phase in an extended family of
materials, ranging from insulators and semiconductors to metals and
superconductors, that have been either identified recently or perceived for
many decades as conventional antiferromagnets
Band structure of CuMnAs probed by optical and photoemission spectroscopy
5 pages, 5 figures + Supplementary InformationTetragonal phase of CuMnAs progressively appears as one of the key materials
for antiferromagnetic spintronics due to efficient current-induced spin-orbit
torques whose existence can be directly inferred from crystal symmetry.
Theoretical understanding of spintronic phenomena in this material, however,
relies on the detailed knowledge of electronic structure (band structure and
corresponding wave functions) which has so far been tested only to a limited
extent. We show that AC permittivity (obtained from ellipsometry) and UV
photoelectron spectra agree with density functional calculations. Together with
the x-ray diffraction and precession electron diffraction tomography, our
analysis confirms recent theoretical claim [Phys.Rev.B 96, 094406 (2017)] that
copper atoms occupy lattice positions in the basal plane of the tetragonal unit
cell.We acknowledge support from National Grid Infrastructure MetaCentrum provided under the programme “Projects
of Large Research, Development, and Innovations Infrastructures” (CESNET LM2015042); Grant Agency of the
Czech Republic under Grant No. 15-13436S; CEDAMNF
(CZ.02.1.01/0.0/0.0/15_003/0000358) of the Czech ministry
of education (MŠMT) as well as its LM2015087 and LNSMLNSpin grants; Cariplo Foundation, Grant No. 2013-0726
(MAGISTER); Spanish MINECO under MAT2015-67593-P
project and the ‘Severo Ochoa’ Programme (SEV-2015-0496);
EU FET Open RIA Grant No. 766566; Engineering and
Physical Sciences Research Council Grant No. EP/P019749/1.
P.W. acknowledges support from the Royal Society through a
University Research Fellowship.Peer reviewe
Altermagnetic lifting of Kramers spin degeneracy
Lifted Kramers spin degeneracy (LKSD) has been among the central topics of condensed-matter physics since the dawn of the band theory of solids1,2. It underpins established practical applications as well as current frontier research, ranging from magnetic-memory technology3–7 to topological quantum matter8–14. Traditionally, LKSD has been considered to originate from two possible internal symmetry-breaking mechanisms. The first refers to time-reversal symmetry breaking by magnetization of ferromagnets and tends to be strong because of the non-relativistic exchange origin15. The second applies to crystals with broken inversion symmetry and tends to be comparatively weaker, as it originates from the relativistic spin–orbit coupling (SOC)16–19. A recent theory work based on spin-symmetry classification has identified an unconventional magnetic phase, dubbed altermagnetic20,21, that allows for LKSD without net magnetization and inversion-symmetry breaking. Here we provide the confirmation using photoemission spectroscopy and ab initio calculations. We identify two distinct unconventional mechanisms of LKSD generated by the altermagnetic phase of centrosymmetric MnTe with vanishing net magnetization20–23. Our observation of the altermagnetic LKSD can have broad consequences in magnetism. It motivates exploration and exploitation of the unconventional nature of this magnetic phase in an extended family of materials, ranging from insulators and semiconductors to metals and superconductors20,21, that have been either identified recently or perceived for many decades as conventional antiferromagnets21,24,25