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 Co$_3$O$_4$ 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 Co$_3$O$_4$, 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 Co$_3$O$_4$, 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

Magnetoelectric coupling at the domain level in polycrystalline hexagonal ErMnO3

We explore the impact of a magnetic field on the ferroelectric domain pattern in polycrystalline hexagonal ErMnO3 at cryogenic temperatures. Utilizing piezoelectric force microscopy measurements at 1.65 K, we observe modifications of the topologically protected ferroelectric domain structure induced by the magnetic field. These alterations likely result from strain induced by the magnetic field, facilitated by intergranular coupling in polycrystalline multiferroic ErMnO3. Our findings give insights into the interplay between electric and magnetic properties at the domain scale and represent a so far unexplored pathway for manipulating topologically protected ferroelectric vortex patterns in hexagonal manganites

Magneto-optical assessment of Plasmodium parasite growth via hemozoin crystal size

Hemozoin is a natural biomarker formed during the hemoglobin metabolism of Plasmodium parasites, the causative agents of malaria. The rotating-crystal magneto-optical detection (RMOD) has been developed for its rapid and sensitive detection both in cell cultures and patient samples. In the current article we demonstrate that, besides quantifying the overall concentration of hemozoin produced by the parasites, RMOD can also track the size distribution of the hemozoin crystals. We establish the relations between the magneto-optical signal, the mean parasite age and the median crystal size throughout one erythrocytic cycle of Plasmodium falciparum parasites, where the latter two are determined by optical and scanning electron microscopy, respectively. The significant correlation between the magneto-optical signal and the stage distribution of the parasites indicates that the RMOD method can be utilized for species-specific malaria diagnosis and for the quick assessment of drug efficacy

Local control of improper ferroelectric domains in YMnO3_3

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$_3$ 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