13 research outputs found
In-plane magnetic domains and N\'eel-like domain walls in thin flakes of the room temperature CrTe van der Waals ferromagnet
The recent discovery of magnetic van der Waals materials has triggered a
wealth of investigations in materials science, and now offers genuinely new
prospects for both fundamental and applied research. Although the catalogue of
van der Waals ferromagnets is rapidly expanding, most of them have a Curie
temperature below 300 K, a notable disadvantage for potential applications.
Combining element-selective x-ray magnetic imaging and magnetic force
microscopy, we resolve at room temperature the magnetic domains and domains
walls in micron-sized flakes of the CrTe van der Waals ferromagnet.
Flux-closure magnetic patterns suggesting in-plane six-fold symmetry are
observed. Upon annealing the material above its Curie point (315 K), the
magnetic domains disappear. By cooling back down the sample, a different
magnetic domain distribution is obtained, indicating material stability and
lack of magnetic memory upon thermal cycling. The domain walls presumably have
N\'eel texture, are preferentially oriented along directions separated by 120
degrees, and have a width of several tens of nanometers. Besides microscopic
mapping of magnetic domains and domain walls, the coercivity of the material is
found to be of a few mT only, showing that the CrTe compound is
magnetically soft. The coercivity is found to increase as the volume of the
material decreases
Stability of the In-Plane Room Temperature van der Waals Ferromagnet Chromium Ditelluride and Its Conversion to Chromium-Interleaved CrTe Compounds
Van der Waals magnetic materials are building blocks for novel kinds of
spintronic devices and playgrounds for exploring collective magnetic phenomena
down to the two-dimensional limit. Chromium-tellurium compounds are relevant in
this perspective. In particular, the 1 phase of CrTe has been argued to
have a Curie temperature above 300~K, a rare and desirable property in the
class of lamellar materials, making it a candidate for practical applications.
However, recent literature reveals a strong variability in the reported
properties, including magnetic ones. Using electron microscopy, diffraction and
spectroscopy techniques, together with local and macroscopic magnetometry
approaches, our work sheds new light on the structural, chemical and magnetic
properties of bulk 1-CrTe exfoliated in the form of flakes having a
thickness ranging from few to several tens of nanometers. We unambiguously
establish that 1-CrTe flakes are ferromagnetic above room temperature,
have an in-plane easy axis of magnetization, low coercivity, and we confirm
that their Raman spectroscopy signatures are two modes,
(103.5~cm) and (136.5~cm). We also prove that
thermal annealing causes a phase transformation to monoclinic CrTe and,
to a lesser extent, to trigonal CrTe. In sharp contrast with
1-CrTe, none of these compounds have a Curie temperature above room
temperature, and they both have perpendicular magnetic anisotropy. Our findings
reconcile the apparently conflicting reports in the literature and open
opportunities for phase-engineered magnetic properties
Room temperature 2D ferromagnetism in few-layered 1-CrTe
Spin-related electronics using two dimensional (2D) van der Waals (vdW)
materials as a platform are believed to hold great promise for revolutionizing
the next generation spintronics. Although many emerging new phenomena have been
unravelled in 2D electronic systems with spin long-range orderings, the
scarcely reported room temperature magnetic vdW material has thus far hindered
the related applications. Here, we show that intrinsic ferromagnetically
aligned spin polarization can hold up to 316 K in a metallic phase of
1-CrTe in the few-layer limit. This room temperature 2D long range
spin interaction may be beneficial from an itinerant enhancement. Spin
transport measurements indicate an in-plane room temperature negative
anisotropic magnetoresistance (AMR) in few-layered CrTe, but a sign
change in the AMR at lower temperature, with -0.6 at 300 K and +5 at 10
K, respectively. This behavior may originate from the specific spin polarized
band structure of CrTe. Our findings provide insights into magnetism in
few-layered CrTe, suggesting potential for future room temperature
spintronic applications of such 2D vdW magnets.Comment: 9 Pages, 4 Figure
Magnetic Phase Diagram of van der Waals Antiferromagnet TbTe3
Terbium tritelluride, TbTe3, orders antiferromagnetically in three steps at TN1 = 6.7 K, TN2 = 5.7 K, and TN3 = 5.4 K, preceded by a correlation hump in magnetic susceptibility at T* ~8 K. Combining thermodynamic, i.e., specific heat Cp and magnetization M, and transport, i.e., resistance R, measurements we established the boundaries of two commensurate and one charge density wave modulated phases in a magnetic field oriented along principal crystallographic axes. Based on these measurements, the magnetic phase diagrams of TbTe3 at H‖a, H‖b and H‖c were constructed
Bilayer splitting versus Fermi-surface warping as an origin of slow oscillations of in-plane magnetoresistance in rare-earth tritellurides
International audienc
Magnetic Phase Diagram of van der Waals Antiferromagnet TbTe<sub>3</sub>
Terbium tritelluride, TbTe3, orders antiferromagnetically in three steps at TN1 = 6.7 K, TN2 = 5.7 K, and TN3 = 5.4 K, preceded by a correlation hump in magnetic susceptibility at T* ~8 K. Combining thermodynamic, i.e., specific heat Cp and magnetization M, and transport, i.e., resistance R, measurements we established the boundaries of two commensurate and one charge density wave modulated phases in a magnetic field oriented along principal crystallographic axes. Based on these measurements, the magnetic phase diagrams of TbTe3 at H‖a, H‖b and H‖c were constructed
Anisotropy-Tuned Magnetic Order in Pyrochlore Iridates
International audienc
Possible high temperature superconducting transitions in disordered graphite obtained from room temperature deintercalated KC
Although progress with twisted graphene nano-devices is boosting the
superconductivity that is the consequence of their Moir\'e flat electronic
bands, the immense choice for future development is an obstacle for their
optimisation. We report here that soft-chemistry deintercalation of KC
breaks down graphite stacking generating a strong disorder that includes
stacking twists and variable local doping. We obtain a bulk graphite whose
individual crystallites have different stackings with arbitrary twists and
doping, scanning in the same sample a huge number of stacking configurations.
We perform magnetisation measurements on batches with different synthesis
conditions. The disorder weakens the huge diamagnetism of graphite, revealing
several phase transitions. A "ferromagnetic-like" magnetisation appears with
Curie temperatures T450K, that has to be subtracted from the measured
magnetisation. Depending on sample synthesis, anomalies towards diamagnetic
states appear at T110K (3 samples), 240K (4 samples),
320K (2 samples). Electrical resistivity measurements yield anomalies for
the T240K transition, with one sample showing a 90% drop. We discuss
the possibility that these (diamagnetic and resistitive) anomalies could be due
to superconductivity.Comment: 15 pages, 10 figure