Room temperature multiferroicity in Bi(4.2)K(0.8)Fe(2)O(9+δ)

Transverse oscillating bubble enhanced laser-driven betatron X-ray radiation generation

Ultrafast high-brightness X-ray pulses have proven invaluable for a broad range of research. Such pulses are typically generated via synchrotron emission from relativistic electron bunches using large-scale facilities. Recently, significantly more compact X-ray sources based on laser-wakefield accelerated (LWFA) electron beams have been demonstrated. In particular, laser-driven sources, where the radiation is generated by transverse oscillations of electrons within the plasma accelerator structure (so-called betatron oscillations) can generate highly-brilliant ultrashort X-ray pulses using a comparably simple setup. Here, we experimentally demonstrate a method to markedly enhance the parameters of LWFA-driven betatron X-ray emission in a proof-of-principle experiment. We show a significant increase in the number of generated photons by specifically manipulating the amplitude of the betatron oscillations by using our novel Transverse Oscillating Bubble Enhanced Betatron Radiation scheme. We realize this through an orchestrated evolution of the temporal laser pulse shape and the accelerating plasma structure. This leads to controlled off-axis injection of electrons that perform large-amplitude collective transverse betatron oscillations, resulting in increased radiation emission. Our concept holds the promise for a method to optimize the X-ray parameters for specific applications, such as time-resolved investigations with spatial and temporal atomic resolution or advanced high-resolution imaging modalities, and the generation of X-ray beams with even higher peak and average brightness.

Associations between objectively assessed physical fitness levels and sleep quality in community-dwelling elderly people in South China

PURPOSE

The aim of this study was to explore associations between objectively assessed physical fitness levels and sleep quality in community-dwelling elderly people in South China.

METHODS

One thousand one hundred thirty-six (504 males and 632 females) community-dwelling adults aged ≥ 50 years old in Dongguan City, South China, were included in the cross-sectional study. All the participants were asked to complete all prepared multi-instrument questionnaire, including the Pittsburgh Sleep Quality Index (Chinese version), for the assessment of the sleep quality and information regarding socio-demographic characteristics, lifestyle, and physical health data. Physical fitness was measured by grip strength, one-leg standing test (OLST) with eyes open, back scratch test, and the forced vital capacity (FVC).

RESULTS

The percentage of poor sleep quality among elderly people (≥ 50 years old) was up to 18.2%. Lower FVC was associated with the poorer sleep quality (adjusted OR = 0.74 per SD increase; P = 0.009), and participants with lower performance in back scratch test were more likely to suffer poor sleep quality (adjusted OR = 1.17 per SD increase; P = 0.035). The independent contribution of physical fitness tests results on the risk of poor sleep quality was 22.1%.

CONCLUSIONS

Our results indicated that sleep quality was strongly associated with physical fitness among community-dwelling elderly people; the lower of the physical fitness predicted poorer sleep quality.

Giant Room-Temperature Magnetodielectric Response in a MOF at 0.1 Tesla

A giant room-temperature magnetodielectric (MD) response upon the application of a small magnetic field is of fundamental importance for the practical application of a new generation of devices. Here, the giant room-temperature magnetodielectric response is demonstrated in the metal-organic framework (MOF) of [NH₂ (CH₃ )₂ ]_n [Fe^III Fe^II_(1-x) Ni^II_x (HCOO)₆ ]_n (x ≈ 0.63-0.69) (1) with its MD coefficient remaining between -20% and -24% in the 300-410 K temperature range, even at 0.1 T. Because a room-temperature magnetodielectric response has never been observed in MOFs, the present work not only provides a new type of magnetodielectric material but also takes a solid step toward the practical application of MOFs in a new generation of devices.

Structural evolution from Bi4.2K0.8Fe2O9+δ nanobelts to BiFeO3 nanochains in vacuum and their multiferroic properties

In this paper, we report the structural evolution of Bi(4.2)K(0.8)Fe(2)O(9+δ) nanobelts to BiFeO3 nanochains and the related variations in multiferroic properties. By using in situ transmission electron microscopy with comprehensive characterization, it was found that the layered perovskite multiferroic Bi(4.2)K(0.8)Fe(2)O(9+δ) nanobelts were very unstable in a vacuum environment, with Bi being easily removed. Based on this finding, a simple vacuum annealing method was designed which successfully transformed the Bi(4.2)K(0.8)Fe(2)O(9+δ) nanobelts into one-dimensional BiFeO(3) nanochains. Both the Bi(4.2)K(0.8)Fe(2)O(9+δ) nanobelts and the BiFeO3 nanochains showed multiferroic behavior, with their ferroelectric and ferromagnetic properties clearly established by piezoresponse and magnetic measurements, respectively. Interestingly, the BiFeO(3) nanochains had a larger magnetization than the Bi(4.2)K(0.8)Fe(2)O(9+δ) nanobelts. Moreover, the BiFeO(3) nanochains exhibited a surprisingly large exchange bias with small training effects. This one-dimensional BiFeO(3) multiferroic nanostructure characterized by a relatively stable exchange bias offers important functionalities that may be attractive for device applications.

Polarization enhancement and ferroelectric switching enabled by interacting magnetic structures in DyMnO₃ thin films

The mutual controls of ferroelectricity and magnetism are stepping towards practical applications proposed for quite a few promising devices in which multiferroic thin films are involved. Although ferroelectricity stemming from specific spiral spin ordering has been reported in highly distorted bulk perovskite manganites, the existence of magnetically induced ferroelectricity in the corresponding thin films remains an unresolved issue, which unfortunately halts this step. In this work, we report magnetically induced electric polarization and its remarkable response to magnetic field (an enhancement of ~800% upon a field of 2 Tesla at 2 K) in DyMnO₃ thin films grown on Nb-SrTiO₃ substrates. Accompanying with the large polarization enhancement, the ferroelectric coercivity corresponding to the magnetic chirality switching field is significantly increased. A picture based on coupled multicomponent magnetic structures is proposed to understand these features. Moreover, different magnetic anisotropy related to strain-suppressed GdFeO₃-type distortion and Jahn-Teller effect is identified in the films.