36 research outputs found
Recommended from our members
Dressed j eff-1/2 objects in mixed-valence lacunar spinel molybdates
The lacunar-spinel chalcogenides exhibit magnetic centers in the form of transition-metal tetrahedra. On the basis of density-functional computations, the electronic ground state of an Mo413+ tetrahedron has been postulated as single-configuration a12 e4 t25, where a1, e, and t2 are symmetry-adapted linear combinations of single-site Mo t2g atomic orbitals. Here we unveil the many-body tetramer wave-function: we show that sizable correlations yield a weight of only 62% for the a12 e4 t25 configuration. While spin–orbit coupling within the peculiar valence orbital manifold is still effective, the expectation value of the spin–orbit operator and the g factors deviate from figures describing nominal t5jeff = 1/2 moments. As such, our data documents the dressing of a spin–orbit jeff = 1/2 object with intra-tetramer excitations. Our results on the internal degrees of freedom of these magnetic moments provide a solid theoretical starting point in addressing the intriguing phase transitions observed at low temperatures in these materials
Dressed jeff-1/2 objects in mixed-valence lacunar spinel molybdates
The lacunar-spinel chalcogenides exhibit magnetic centers in the form of transition-metal tetrahedra. On the basis of density-functional computations, the electronic ground state of an Mo413+ tetrahedron has been postulated as single-configuration a12 e4 t25, where a1, e, and t2 are symmetry-adapted linear combinations of single-site Mo t2g atomic orbitals. Here we unveil the many-body tetramer wave-function: we show that sizable correlations yield a weight of only 62% for the a12 e4 t25 configuration. While spin–orbit coupling within the peculiar valence orbital manifold is still effective, the expectation value of the spin–orbit operator and the g factors deviate from figures describing nominal t5 jeff = 1/2 moments. As such, our data documents the dressing of a spin–orbit jeff = 1/2 object with intra-tetramer excitations. Our results on the internal degrees of freedom of these magnetic moments provide a solid theoretical starting point in addressing the intriguing phase transitions observed at low temperatures in these materials
Fast non-volatile electric control of antiferromagnetic states
Electrical manipulation of antiferromagnetic states, a cornerstone of
antiferromagnetic spintronics, is a great challenge, requiring novel material
platforms. Here we report the full control over antiferromagnetic states by
voltage pulses in the insulating CoO spinel. We show that the strong
linear magnetoelectric effect emerging in its antiferromagnetic state is fully
governed by the orientation of the N\'eel vector. As a unique feature of
CoO, the magnetoelectric energy can easily overcome the weak
magnetocrystalline anisotropy, thus, the N\'eel vector can be manipulated on
demand, either rotated smoothly or reversed suddenly, by combined electric and
magnetic fields. We succeed with switching between antiferromagnetic states of
opposite N\'eel vectors by voltage pulses within a few microsecond in
macroscopic volumes. These observations render quasi-cubic antiferromagnets,
like CoO, an ideal platform for the ultrafast (pico- to nanosecond)
manipulation of microscopic antiferromagnetic domains and may pave the way for
the realization of antiferromagnetic spintronic devices.Comment: 7 pages, 3 figure
Strain driven conducting domain walls in a Mott insulator
Rewritable nanoelectronics offers new perspectives and potential to both
fundamental research and technological applications. Such interest has driven
the research focus into conducting domain walls: pseudo 2D conducting channels
that can be created, positioned, and deleted in situ. However, the study of
conductive domain walls is largely limited to wide-gap ferroelectrics, where
the conductivity typically arises from changes in charge carrier density, due
to screening charge accumulation at polar discontinuities. This work shows
that, in narrow-gap correlated insulators with strong charge lattice coupling,
local strain gradients can drive enhanced conductivity at the domain walls,
removing polar discontinuities as a criteria for conductivity. By combining
different scanning probe microscopy techniques, we demonstrate that the domain
wall conductivity in GaV4S8 does not follow the established screening charge
model but rather arises from the large surface reconstruction across the
Jahn-Teller transition and the associated strain gradients across the domain
walls. This mechanism can turn any structural, or even magnetic, domain wall
conducting, if the electronic structure of the host is susceptible to local
strain gradients, drastically expanding the range of materials and phenomena
that may be applicable to domain wall based nanoelectronics
Direct imaging of spatial heterogeneities in type II superconductors
Understanding the exotic properties of quantum materials, including
high-temperature superconductors, remains a formidable challenge that demands
direct insights into electronic conductivity. Current methodologies either
capture a bulk average or near-atomically-resolved information, missing direct
measurements at the critical intermediate length scales. Here, using the
superconductor Fe(Se,Te) as a model system, we use low-temperature conductive
atomic force microscopy (cAFM) to bridge this gap. Contrary to the uniform
superconductivity anticipated from bulk assessments, cAFM uncovers micron-scale
conductive intrusions within a relatively insulating matrix. Subsequent
compositional mapping through atom probe tomography, shows that differences in
conductivity correlated with local changes in composition. cAFM, supported by
advanced microscopy and microanalysis, represents a methodological breakthrough
that can be used to navigate the intricate landscape of high-temperature
superconductors and the broader realm of quantum materials. Such fundamental
information is critical for theoretical understanding and future guided design
Magnetization reversal through an antiferromagnetic state
Magnetization reversal in ferro- and ferrimagnets is a well-known archetype of non-equilibrium processes, where the volume fractions of the oppositely magnetized domains vary and perfectly compensate each other at the coercive magnetic field. Here, we report on a fundamentally new pathway for magnetization reversal that is mediated by an antiferromagnetic state. Consequently, an atomic-scale compensation of the magnetization is realized at the coercive field, instead of the mesoscopic or macroscopic domain cancellation in canonical reversal processes. We demonstrate this unusual magnetization reversal on the Zn-doped polar magnet Fe2Mo3O8. Hidden behind the conventional ferrimagnetic hysteresis loop, the surprising emergence of the antiferromagnetic phase at the coercive fields is disclosed by a sharp peak in the field-dependence of the electric polarization. In addition, at the magnetization reversal our THz spectroscopy studies reveal the reappearance of the magnon mode that is only present in the pristine antiferromagnetic state. According to our microscopic calculations, this unusual process is governed by the dominant intralayer coupling, strong easy-axis anisotropy and spin fluctuations, which result in a complex interplay between the ferrimagnetic and antiferromagnetic phases. Such antiferro-state-mediated reversal processes offer novel concepts for magnetization control, and may also emerge for other ferroic orders.</p
Magnetic and crystal structure of the antiferromagnetic skyrmion candidate GdSb0.71Te1.22
GdSb0.46Te1.48, a nonsymmorphic Dirac semimetal with Dirac nodes at the Fermi level, has a rich magnetic phase diagram with one of the phases predicted to be an antiferromagnetic skyrmion state. In the current work, we investigate GdSb0.71Te1.22 through bulk magnetization measurements, single-crystal, and powder synchrotron X-ray diffraction, as well as single-crystal hot-neutron diffraction. We resolve a weak orthorhombic distortion with respect to the tetragonal structure and charge density wave (CDW) satellites due to incommensurate modulations of the crystal structure. At 2 K the magnetic structure is modulated with two propagation vectors, kI = (0.45 0 0.45) and kII = (0.4 0 0), with all their arms visible. While kI persists up to the transition to the paramagnetic state at TN = 11.9 K, kII disappears above an intermediate magnetic transition at T1 = 5 K. Whereas magnetic field applied along the c-axis has only a weak effect on the intensity of antiferromagnetic reflections, it is effective in inducing an additional ferromagnetic component on Gd atoms. We refine possible magnetic structures of GdSb0.71Te1.22 and discuss the possibility of hosting magnetic textures with non-trivial 3D+ 2 topologies in the GdSb1−xTe1+x series.ISSN:0925-8388ISSN:1873-466