23 research outputs found
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
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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
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
Magnetic avalanche of non-oxide conductive domain walls
Atomically sharp domain walls (DWs) in ferroelectrics are considered as an
ideal platform to realize easy-to-reconfigure nanoelectronic building blocks,
created, manipulated and erased by external fields. However, conductive DWs
have been exclusively observed in oxides, where DW mobility and conductivity is
largely influenced by stoichiometry and defects. In contrast, we here report on
conductive DWs in the non-oxide ferroelectric GaVS, where charge
carriers are provided intrinsically by multivalent V molecular clusters. We
show that this new mechanism gives rise to DWs composed of nanoscale stripes
with alternating electron and hole conduction, unimaginable in oxides. By
exerting magnetic control on these segments we promote the mobile and
effectively 2D DWs into dominating the 3D conductance, triggering abrupt
conductance changes as large as eight orders of magnitude. The flexible
valency, as origin of these novel hybrid DWs with giant conductivity,
demonstrates that non-oxide ferroelectrics can be the source of novel phenomena
beyond the realm of oxide electronics.Comment: 8 pages, 4 figure
Squeezing the periodicity of Néel-type magnetic modulations by enhanced Dzyaloshinskii-Moriya interaction of 4d electrons
In polar magnets, such as GaVS, GaVSe and VOSeO, modulated magnetic phases namely the cycloidal and the Néel-type skyrmion lattice states were identified over extended temperature ranges, even down to zero Kelvin. Our combined small-angle neutron scattering and magnetization study shows the robustness of the Néel-type magnetic modulations also against magnetic fields up to 2 T in the polar GaMoS. In addition to the large upper critical field, enhanced spin-orbit coupling stabilize cycloidal, Néel skyrmion lattice phases with sub-10 nm periodicity and a peculiar distribution of the magnetic modulation vectors. Moreover, we detected an additional single-q state not observed in any other polar magnets. Thus, our work demonstrates that non-centrosymmetric magnets with 4d and 5d electron systems may give rise to various highly compressed modulated states
Macroscopic Manifestation of Domain-wall Magnetism and Magnetoelectric Effect in a N\'eel-type Skyrmion Host
We report a magnetic state in GaVSe which emerges exclusively in
samples with mesoscale polar domains and not in polar mono-domain crystals. Its
onset is accompanied with a sharp anomaly in the magnetic susceptibility and
the magnetic torque, distinct from other anomalies observed also in polar
mono-domain samples upon transitions between the cycloidal, the N\'eel-type
skyrmion lattice and the ferromagnetic states. We ascribe this additional
transition to the formation of magnetic textures localized at structural domain
walls, where the magnetic interactions change stepwise and spin textures with
different spiral planes, hosted by neighbouring domains, need to be matched. A
clear anomaly in the magneto-current indicates that the domain-wall-confined
magnetic states also have strong contributions to the magnetoelectric response.
We expect polar domain walls to commonly host such confined magnetic edge
states, especially in materials with long wavelength magnetic order