38 research outputs found
Highly efficient room-temperature nonvolatile magnetic switching by current in Fe3GaTe2 thin flakes
Effectively tuning magnetic state by using current is essential for novel
spintronic devices. Magnetic van der Waals (vdW) materials have shown superior
properties for the applications of magnetic information storage based on the
efficient spin torque effect. However, for most of known vdW ferromagnets, the
ferromagnetic transition temperatures lower than room temperature strongly
impede their applications and the room-temperature vdW spintronic device with
low energy consumption is still a long-sought goal. Here, we realize the highly
efficient room-temperature nonvolatile magnetic switching by current in a
single-material device based on vdW ferromagnet Fe3GaTe2. Moreover, the
switching current density and power dissipation are about 300 and 60000 times
smaller than conventional spin-orbit-torque devices of magnet/heavymetal
heterostructures. These findings make an important progress on the applications
of magnetic vdW materials in the fields of spintronics and magnetic information
storage.Comment: 18 page2, 4 figure
Pressure-tunable magnetic topological phases in magnetic topological insulator MnSb4Te7
Magnetic topological insulators, possessing both magnetic order and
topological electronic structure, provides an excellent platform to research
unusual physical properties. Here, we report a high-pressure study on the
anomalous Hall effect of magnetic TI MnSb4Te7 through transports measurements
combined with first-principle theoretical calculations. We discover that the
ground state of MnSb4Te7 experiences a magnetic phase transition from the
A-type antiferromagnetic state to ferromagnetic dominating state at 3.78 GPa,
although its crystal sustains a rhombohedral phase under high pressures up to 8
GPa. The anomalous Hall conductance {\sigma}xyA keeps around 10 {\Omega}-1
cm-1, dominated by the intrinsic mechanism even after the magnetic phase
transition. The results shed light on the intriguing magnetism in MnSb4Te7 and
pave the way for further studies of the relationship between topology and
magnetism in topological materials.Comment: 10 pages, 4 figure
Evidence of Noncollinear Spin Texture in Magnetic Moir\'e Superlattices
Moir\'e magnetism, parallel with moir\'e electronics that has led to novel
correlated and topological electronic states, emerges as a new venue to design
and control exotic magnetic phases in twisted magnetic two-dimensional(2D)
crystals. Here, we report direct evidence of noncollinear spin texture in 2D
twisted double bilayer (tDB) magnet chromium triiodide (CrI). Using
magneto-optical spectroscopy in tDB CrI, we revealed the presence of a net
magnetization, unexpected from the composing antiferromagnetic bilayers with
compensated magnetizations, and the emergence of noncollinear spins, originated
from the moir\'e exchange coupling-induced spin frustrations. Exploring the
twist angle dependence, we demonstrated that both features are present in tDB
CrI with twist angles from 0.5 to 5, but are most prominent in the
1.1 tDB CrI. Focusing on the temperature dependence of the 1.1 tDB
CrI, we resolved the dramatic suppression in the net magnetization onset
temperature and the significant softening of noncollinear spins, as a result of
the moir\'e induced frustration. Our results demonstrate the power of moir\'e
superlattices in introducing novel magnetic phenomena that are absent in
natural 2D magnets
Magnetic topological insulator MnBi6Te10 with zero-field ferromagnetic state and gapped Dirac surface states
Magnetic topological insulators (TIs) with nontrivial topological electronic
structure and broken time-reversal symmetry exhibit various exotic topological
quantum phenomena. The realization of such exotic phenomena at high temperature
is one of central topics in this area. We reveal that MnBi6Te10 is a magnetic
TI with an antiferromagnetic ground state below 10.8 K whose nontrivial
topology is manifested by Dirac-like surface states. The ferromagnetic axion
insulator state with Z4 = 2 emerges once spins polarized at field as low as 0.1
T, accompanied with saturated anomalous Hall resistivity up to 10 K. Such a
ferromagnetic state is preserved even external field down to zero at 2 K.
Theoretical calculations indicate that the few-layer ferromagnetic MnBi6Te10 is
also topologically nontrivial with a non-zero Chern number. Angle-resolved
photoemission spectroscopy experiments further reveal three types of Dirac
surface states arising from different terminations on the cleavage surfaces,
one of which has insulating behavior with an energy gap of ~ 28 meV at the
Dirac point. These outstanding features suggest that MnBi6Te10 is a promising
system to realize various topological quantum effects at zero field and high
temperature.Comment: 18 pages, 4 figures and 1 tabl
Pressure induced superconductivity in WB2 and ReB2 through modifying the B layers
The recent discovery of superconductivity up to 32 K in the pressurized MoB2
reignites the interests in exploring high-Tc superconductors in
transition-metal diborides. Inspired by that work, we turn our attention to the
5d transition-metal diborides. Here we systematically investigate the responses
of both structural and physical properties of WB2 and ReB2 to external
pressure, which possess different types of boron layers. Similar to MoB2, the
pressure-induced superconductivity was also observed in WB2 above 60 GPa with a
maximum Tc of 15 K at 100 GPa, while no superconductivity was detected in ReB2
in this pressure range. Interestingly, the structures at ambient pressure for
both WB2 and ReB2 persist to high pressure without structural phase
transitions. Theoretical calculations suggest that the ratio of flat boron
layers in this class of transition-metal diborides may be crucial for the
appearance of high Tc. The combined theoretical and experimental results
highlight the effect of geometry of boron layers on superconductivity and shed
light on the exploration of novel high-Tc superconductors in borides.Comment: 17 pages,5 figure
Magnetic field-induced quantum phase transitions in a van der Waals magnet
Exploring new parameter regimes to realize and control novel phases of matter
has been a main theme in modern condensed matter physics research. The recent
discovery of 2D magnetism in nearly freestanding monolayer atomic crystals has
already led to observations of a number of novel magnetic phenomena absent in
bulk counterparts. Such intricate interplays between magnetism and crystalline
structures provide ample opportunities for exploring quantum phase transitions
in this new 2D parameter regime. Here, using magnetic field and temperature
dependent circularly polarized Raman spectroscopy of phonons and magnons, we
map out the phase diagram of CrI3 that has been known to be a layered AFM in
its 2D films and a FM in its 3D bulk. We, however, reveal a novel mixed state
of layered AFM and FM in 3D CrI3 bulk crystals where the layered AFM survives
in the surface layers and the FM appears in deeper bulk layers. We then show
that the surface layered AFM transits into the FM at a critical magnetic field
of 2 T, similar to what was found in the few layer case. Interestingly,
concurrent with this magnetic phase transition, we discover a first-order
structural phase transition that alters the crystallographic point group from
C3i to C2h and thus, from a symmetry perspective, this monoclinic structural
phase belongs to the 3D nematic order universality class. Our result not only
unveils the complex single magnon behavior in 3D CrI3, but also settles down
the puzzle of how CrI3 transits from a bulk FM to a thin layered AFM
semiconductor, despite recent efforts in understanding the origin of layered
AFM in CrI3 thin layer, and reveals the intimate relationship between the
layered AFM-to-FM and the crystalline rhombohedral-to-monoclinic phase
transitions. These findings further open up opportunities for future 2D
magnet-based magneto-mechanical devices