ABSTRACT
Layered ferromagnets with strong magnetic anisotropy energy (MAE) have special applications in nanoscale memory elements in electronic circuits. Here, we report a strain tunability of perpendicular magnetic anisotropy in van der Waals (vdW) ferromagnets VI3 using magnetic circular dichroism measurements. For an unstrained flake, the M-H curve shows a rectangular-shaped hysteresis loop with a large coercivity (1.775 T at 10 K) and remanent magnetization. Furthermore, the coercivity can be enhanced to a maximum of 2.6 T under a 3.8% external in-plane tensile strain. Our DFT calculations show that the increased MAE under strain contributes to the enhancement of coercivity. Meanwhile, the strain tunability on the coercivity of CrI3, with a similar crystal structure, is limited. The main reason is the strong spin-orbit coupling in V3+ in VI6 octahedra in comparison with that in Cr3+. The strain tunability of coercivity in VI3 flakes highlights its potential for integration into vdW heterostructures.
ABSTRACT
The band level landscape in quantum dots is of great significance toward achieving stable and efficient electroluminescent devices. A series of quantum dots with specific emission and band structure of the intermediate layer is designed, including rich CdS (R-CdS), thick ZnSe (T-ZnSe), thin ZnSe (t-ZnSe) and ZnCdS (R-ZnCdS) intermediate alloy shell layers. These quantum dots in QLEDs show superior performance, including maximum current efficiency, external quantum efficiencies and a T50 lifetime (at 1000 cd/m2) of 47.2 cd/A, 11.2% and 504 h for R-CdS; 61.6 cd/A, 14.7% and 612 h for t-ZnSe; 70.5 cd/A, 16.8% and 924 h for T-ZnSe; and 82.0 cd/A, 19.6% and 1104 h for R-ZnCdS. Among them, the quantum dots with the ZnCdS interlayer exhibit deep electron confinement and shallow hole confinement capabilities, which facilitate the efficient injection and radiative recombination of carriers into the emitting layer. Furthermore, the optimal devices show a superior T50 lifetime of more than 1000 h. The proposed novel methodology of quantum dot band engineering is expected to start a new way for further enhancing QLED exploration.
ABSTRACT
BACKGROUND: Internal rectal prolapse (IRP) is one of the most common causes of obstructive constipation. The incidence of IRP in women is approximately three times that in men. IRP is mainly treated by surgery, which can be divided into two categories: Abdominal procedures and perineal procedures. This study offers a better procedure for the treatment of IRP. AIM: To compare the clinical efficacy of laparoscopic integral pelvic floor/ligament repair (IPFLR) combined with a procedure for prolapse and hemorrhoids (PPH) and the laparoscopic IPFLR alone in the treatment of IRP in women. METHODS: This study collected the clinical data of 130 female patients with IRP who underwent surgery from January 2012 to October 2014. The patients were divided into groups A and B. Group A had 63 patients who underwent laparoscopic IPFLR alone, and group B had 67 patients who underwent the laparoscopic IPFLR combined with PPH. The degree of internal rectal prolapse (DIRP), Wexner constipation scale (WCS) score, Wexner incontinence scale (WIS) score, and Gastrointestinal Quality of Life Index (GIQLI) score were compared between groups and within groups before surgery and 6 mo and 2 years after surgery. RESULTS: All laparoscopic surgeries were successful. The general information, number of bowel movements before surgery, DIRP, GIQLI score, WIS score, and WCS score before surgery were not significantly different between the two groups (all P > 0.05). The WCS score, WIS score, GIQLI score, and DIRP in each group 6 mo, and 2 years after surgery were significantly better than before surgery (P < 0.001). In group A, the DIRP and WCS score gradually improved from 6 mo to 2 years after surgery (P < 0.001), and the GIQLI score progressively improved from 6 mo to 2 years after surgery (P < 0.05). In group B, the DIRP, WCS score and WIS score significantly improved from 6 mo to 2 years after surgery (P < 0.05), and the GIQLI score 2 years after surgery was significantly higher than that 6 mo after surgery (P < 0.05). The WCS score, WIS score, GIQLI score, and DIRP of group B were significantly better than those of group A 6 mo and 2 years after surgery (all P < 0.001, Bonferroni) except DIRP at 2 years after surgery. There was a significant difference in the recurrence rate of IRP between the two groups 6 mo after surgery (P = 0.011). There was no significant difference in postoperative grade I-III complications between the two groups (P = 0.822). CONCLUSION: Integral theory-guided laparoscopic IPFLR combined with PPH has a higher cure rate and a better clinical efficacy than laparoscopic IPFLR alone.
ABSTRACT
Circularly polarized light carries light spin angular momentum, which may lead helicity-resolved Raman scattering to be sensitive to the electronic spin configuration in magnetic materials. Here, we demonstrate that all Raman modes in the 2D ferromagnet VI3 show different scattering intensities to left and right circularly polarized light at low temperatures, which gives direct evidence of the time-reversal symmetry breaking. By measuring the circular polarization of the dominant Raman mode with respect to the temperature and magnetic field, the ferromagnetic (FM) phase transition and hysteresis behavior can be clearly resolved. Besides the lattice excitations, quasielastic scattering is detected in the paramagnetic phase, and it gradually evolves into the acoustic magnon mode at 18.5 cm-1 in the FM state, which gives the spin wave gap that results from large magnetic anisotropy. Our findings demonstrate that helicity-resolved Raman spectroscopy is an effective tool to directly probe the ferromagnetism in 2D magnets.
ABSTRACT
The recent discovery of 2D magnets has revealed various intriguing phenomena due to the coupling between spin and other degrees of freedoms (such as helical photoluminescence, nonreciprocal SHG). Previous research on the spin-phonon coupling effect mainly focuses on the renormalization of phonon frequency. Here we demonstrate that the Raman polarization selection rules of optical phonons can be greatly modified by the magnetic ordering in 2D magnet CrI3. For monolayer samples, the dominant A1g peak shows an abnormally high intensity in the cross-polarization channel at low temperatures, which is forbidden by the selection rule based on the lattice symmetry. For the bilayer, this peak is absent in the cross-polarization channel for the layered antiferromagnetic (AFM) state and reappears when it is tuned to the ferromagnetic (FM) state by an external magnetic field. Our findings shed light on exploring the emergent magneto-optical effects in 2D magnets.
