34 research outputs found
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
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
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
Redshifted 21-cm bispectrum II: Impact of the spin temperature fluctuations and redshift space distortions on the signal from the Cosmic Dawn
We present a study of the 21-cm signal bispectrum (which quantifies the
non-Gaussianity in the signal) from the Cosmic Dawn (CD). For our analysis, we
have simulated the 21-cm signal using radiative transfer code GRIZZLY, while
considering two types of sources (mini-QSOs and HMXBs) for Ly coupling
and the X-ray heating of the IGM. Using this simulated signal, we have, for the
first time, estimated the CD 21-cm bispectra for all unique -triangles and
for a range of modes. We observe that the redshift evolution of the
bispectra magnitude and sign follow a generic trend for both source models.
However, the redshifts at which the bispectra magnitude reach their maximum and
minimum values and show their sign reversal depends on the source model. When
the Ly coupling and the X-ray heating of the IGM occur simultaneously,
we observe two consecutive sign reversals in the bispectra for small
-triangles (irrespective of the source models). One arising at the beginning
of the IGM heating and the other at the end of Ly coupling saturation.
This feature can be used in principle to constrain the CD history and/or to
identify the specific CD scenarios. We also quantify the impact of the spin
temperature () fluctuations on the bispectra. We find that fluctuations have maximum impact on the bispectra magnitude for small
-triangles and at the stage when Ly coupling reaches saturation.
Furthermore, we are also the first to quantify the impact of redshift space
distortions (RSD), on the CD bispectra. We find that the impact of RSD on the
CD 21-cm bispectra is significant () and the level depends on the
stages of the CD and the -triangles for which the bispectra are being
estimated.Comment: 15 pages, 9 figures. Accepted for publication in the MNRAS. Replaced
to match the accepted versio