56 research outputs found
Magnetodielectric coupling in a Ru-based 6H-perovskite, Ba3NdRu2O9
A large spin-orbit coupling is a way to control strong magnetodielectric (MD)
coupling in a higher d-orbital materials. However reports are rare on such
compounds due to often leaky conductive behavior. Here, we demonstrate MD
coupling in a Ru-based 6H-perovskite system, Ba3NdRu2O9. The rare-earth ion in
a 6H-perovskite makes the system insulating enough to carry out MD
investigation. The compound is ferromagnetically ordered below 24 K (TC),
followed by another magnetic feature at T~ 17 K (T2). The dielectric constant
clearly traces the magnetic ordering, manifesting a peak at the onset of TC,
which is suppressed by the application of an external magnetic field (H). The
results indicate the presence of MD coupling in this compound, which is further
confirmed by the H-dependence of the dielectric constant. Interestingly, a
cross-over of the sign of MD coupling is observed at T ~ T2. We conclude that
two different mechanism controls the MD coupling which yields positive and
negative coupling, respectively. Both mechanisms are competing as a function of
temperature and magnetic field. This brings us a step closer to design and
control the magnetodielectric effect in 6H-perovskites containing higher
d-orbital elements
Dielectric properties of 3D printed polylactic acid
3D printers constitute a fast-growing worldwide market. These printers are often employed in research and development fields related to engineering or architecture, especially for structural components or rapid prototyping. Recently, there is enormous progress in available materials for enhanced printing systems that allow additive manufacturing of complex functional products, like batteries or electronics. The polymer polylactic acid (PLA) plays an important role in fused filament fabrication, a technique used for commercially available low-budget 3D printers. This printing technology is an economical tool for the development of functional components or cases for electronics, for example, for lab purposes. Here we investigate if the material properties of “as-printed” PLA, which was fabricated by a commercially available 3D printer, are suitable to be used in electrical measurement setups or even as a functional material itself in electronic devices. For this reason, we conduct differential scanning calorimetry measurements and a thorough temperature and frequency-dependent analysis of its dielectric properties. These results are compared to partially crystalline and completely amorphous PLA, indicating that the dielectric properties of “as-printed” PLA are similar to the latter. Finally, we demonstrate that the conductivity of PLA can be enhanced by mixing it with the ionic liquid “trihexyl tetradecyl phosphonium decanoate.” This provides a route to tailor PLA for complex functional products produced by an economical fused filament fabrication
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
Local control of improper ferroelectric domains in YMnO
Improper ferroelectrics are described by two order parameters: a primary one,
driving a transition to long-range distortive, magnetic or otherwise
non-electric order, and the electric polarization, which is induced by the
primary order parameter as a secondary, complementary effect. Using
low-temperature scanning probe microscopy, we show that improper ferroelectric
domains in YMnO can be locally switched by electric field poling. However,
subsequent temperature changes restore the as-grown domain structure as
determined by the primary lattice distortion. The backswitching is explained by
uncompensated bound charges occuring at the newly written domain walls due to
the lack of mobile screening charges at low temperature. Thus, the polarization
of improper ferroelectrics is in many ways subject to the same electrostatics
as in their proper counterparts, yet complemented by additional functionalities
arising from the primary order parameter. Tailoring the complex interplay
between primary order parameter, polarization, and electrostatics is therefore
likely to result in novel functionalities specific to improper ferroelectrics
Multiferroic spin-superfluid and spin-supersolid phases in MnCr2S4
Spin supersolids and spin superfluids reveal complex canted spin structures
with independent order of longitudinal and transverse spin components. This
work addresses the question whether these exotic phases can exhibit spin-driven
ferroelectricity. Here we report the results of dielectric and pyrocurrent
measurements of MnCr2S4 as function of temperature and magnetic field up to 60
T. This sulfide chromium spinel exhibits a Yafet-Kittel type canted spin
structure at low temperatures. As function of external magnetic field, the
manganese spins undergo a sequence of ordering patterns of the transverse and
longitudinal spin components, which can be mapped onto phases as predicted by
lattice-gas models including solid, liquid, super-fluid, and supersolid phases.
By detailed dielectric and pyrocurrent measurements, we document a zoo of
multiferroic phases with sizable ferroelectric polarization strongly varying
from phase to phase. Using lattice-gas terminology, the title compound reveals
multiferroic spin-superfluid and spin-supersolid phases, while the
antiferromagnetic solid is paraelectric.Comment: 14 pages including 5 figure
Magnetic and geometric control of spin textures in the itinerant kagome magnet Fe3Sn2
Magnetic materials with competing magnetocrystalline anisotropy and dipolar energies can develop a wide range of domain patterns, including classical stripe domains, domain branching, and topologically trivial and nontrivial (skyrmionic) bubbles. We image the magnetic domain pattern of Fe3Sn2 by magnetic force microscopy and study its evolution due to geometrical confinement, magnetic fields, and their combination. In Fe3Sn2 lamellae thinner than 3 μm, we observe stripe domains whose size scales with the square root of the lamella thickness, exhibiting classical Kittel scaling. Magnetic fields turn these stripes into a highly disordered bubble lattice. Complementary micromagnetic simulations quantitatively capture the magnetic field and thickness dependence of the magnetic patterns, reveal strong reconstructions of the patterns between the surface and the core of the lamellae, and identify the observed bubbles as skyrmionic bubbles. Our results imply that geometrical confinement together with competing magnetic interactions can provide a path to fine-tune and stabilize different types of topologically trivial and nontrivial spin structures in centrosymmetric magnets
Insulating improper ferroelectric domain walls as robust barrier layer capacitors
We report the dielectric properties of improper ferroelectric h-ErMnO.
From the bulk characterisation we observe a temperature and frequency range
with two distinct relaxation-like features, leading to high and even 'colossal'
values for the dielectric permittivity. One feature trivially originates from
the formation of a Schottky barrier at the electrode-sample interface, whereas
the second one relates to an internal barrier layer capacitance (BLC). The
calculated volume fraction of the internal BLC (of 8 %) is in good agreement
with the observed volume fraction of insulating domain walls (DWs). While it is
established that insulating DWs can give rise to high dielectric constants,
studies typically focused on proper ferroelectrics where electric fields can
remove the DWs. In h-ErMnO, by contrast, the insulating DWs are
topologically protected, facilitating operation under substantially higher
electric fields. Our findings provide the basis for a conceptually new approach
to engineer materials exhibiting colossal dielectric permittivities using
domain walls in improper ferroelecctrics with potential applications in
electroceramic capacitors.Comment: 7 pages, 4 figure
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