Two-dimensional (2D) van der Waals (vdW) ferromagnetic metals FexGeTe2 with x = 3 – 5 have raised significant interest in the scientific community. Fe5GeTe2 shows prospects for spintronic applications since...

Magnetic skyrmions in two-dimensional van der Waals materials provide an ideal platform to push skyrmion technology to the ultimate atomically thin limit. In this work, we theoretically demonstrate the Dzyaloshinskii–Moriya interaction and the formation of a Néel-type skyrmion lattice at the CrTe2/WTe2 bilayer van der Waals heterostructure. Our calculations suggest a field-controlled Néel-type skyrmion lattice—a ferromagnet transition cycle. In addition, a spin-torque induced by spin-polarized current injection was simulated in order to study the motion of a skyrmion on a racetrack, where an increase in the skyrmion Hall angle is observed at high temperatures. Consequently, this study suggests that generation and annihilation of skyrmions can be achieved with temperature or field control and also manipulate the velocity and the direction of the Néel-type skyrmions through ultra-low current densities and temperature, thus shedding light on the general picture of magnetic skyrmion control and design of two-dimensional van der Waals heterostructures.

Polycrystalline ceramic samples and a single crystal of EuTiO3 have been investigated by Raman spectroscopy in the temperature range 80–300 K. Although synchrotron x‐ray diffraction (XRD) data clearly indicated the cubic to tetragonal phase transition around 282 K, no mode from the symmetry allowed Raman active phonons was found in the tetragonal phase, contrary to the case of the homologous SrTiO3. In order to study the evolution of this unique characteristic, ceramics of EuxSr1‐xTiO3 (x = 0.03–1.0) characterized by synchrotron XRD for the structural phase transition have been also investigated by Raman spectroscopy, verifying the very strong influence on the Raman yield by Eu substitution. By applying an external magnetic field or alternatively hydrostatic pressure modes are activated in the Raman spectra. Temperature dependant XAS/XMCD measurements indicate the presence of magnetic interactions even close to room temperature in agreement with previous experimental results also showing the presence of small magnetic interactions deep inside the paramagnetic phase. A possible explanation for the puzzling absence of the Raman modes is proposed related to a strong spin–lattice interaction that drives the cubic to tetragonal structural phase transition and makes the Raman tensor antisymmetric. In this model, the external perturbation will induce a symmetric Raman tensor allowing modes to be present in the spectra.

No abstract

The influence of an external static magnetic field (up to 480 mT) on the structural properties of EuTiO3 (ETO) polycrystalline samples was examined by powder XRD at the Elettra synchrotron facilities in the temperature range 100–300 K. While the cubic to tetragonal structural phase transition temperature in this magnetic field range remains almost unaffected, significant lattice effects appear at two characteristic temperatures (∼200 K and ∼250 K), which become more pronounced at a critical threshold field. At ∼200  K a change in the sign of magnetostriction is detected attributed to a modification of the local magnetic properties from intrinsic ferromagnetism to intrinsic antiferromagnetism. These data are a clear indication that strong spin–lattice interactions govern also the high temperature phase of ETO and trigger the appearance of magnetic domain formation and phase transitions.

One monolayer semimetallic HfTe2 thin films are grown on three substrates with different electronic properties in order to study the substrate effect on the electronic structure of the HfTe2 epilayer. Angle resolved photoelectron spectroscopy measurements indicate that the band features are identical in all three cases, providing evidence that the HfTe2 epilayer does not interact with any of the substrates to form hybridized bands and any band feature originates from the HfTe2 material itself. However, a shift of HfTe2 energy bands is observed among the three cases, which is attributed to substrate electron doping. This paves the way for accessing the Dirac point of HfTe2 Dirac semimetal, which is located about ∼0.2 to 0.3 eV above the Fermi level in the case of suspended HfTe2 in a non-destructive way.

An epitaxial EuTiO3 (ETO) film grown on the SrTiO3 substrate was studied at room temperature with synchrotron XRD and in situ application of an electric field (nominally up to 7.8 kV/cm) in near grazing incidence geometry, in order to monitor the response of the lattice to the field. 2D diffraction images show that apparently misoriented coherently diffracting domains are present close to the surface whereas the film diffracts more as a single crystal towards the interface. Diffraction intensity profiles recorded from the near surface region of the EuTiO3 film showed systematic modifications upon the application of the electric field, indicating that at a critical electric field (nominally above 3.1 kV/cm), there is a clear change in the lattice response to the field, which was much stronger when the field was almost parallel to the diffraction vector. The data suggest that the ETO film, nominally paraelectric at room temperature, transforms under the application of a critical electric field to piezoelectric in agreement with a theoretical analysis based on a double-well potential. In order to exclude effects arising from the substrate, this has been investigated separately and shown not to be affected by the field.

Topotactic transformations of suitable layered three-dimensional precursors are among the most robust methods to prepare two-dimensional (2D) materials based on silicon or germanium. Here we use Density Functional Theory calculations...