Single-phase insulating BiFeO3 ceramics have been synthesized by a simple but effective method that conventional solid state reaction is followed immediately by quenching processing. At room temperature, the ceramics show a metastable, distorted rhombohedral phase and the refined structure parameters are presented based on x-ray diffraction. It is revealed that the formations of Fe2+ and oxygen deficiency are greatly suppressed by the quenching processing. A well-saturated ferroelectric hysteresis loop with a large remnant polarization (2Pr=23.5μC∕cm2) is observed with an applied field of 155kV∕cm. Temperature-dependent magnetic property is investigated and weak ferromagnetism with a remnant magnetization of 4×10−6μB∕Fe at 10K is established. These results may have implications for further studies on multiferroics.

Topological Dirac semimetals (TDSs) represent a new state of quantum matter recently discovered that offers a platform for realizing many exotic physical phenomena. A TDS is characterized by the linear touching of bulk (conduction and valance) bands at discrete points in the momentum space (i.e. 3D Dirac points), such as in Na3Bi and Cd3As2. More recently, new types of Dirac semimetals with robust Dirac line-nodes (with non-trivial topology or near the critical point between topological phase transitions) have been proposed that extends the bulk linear touching from discrete points to 1D lines. In this work, using angle-resolved photoemission spectroscopy (ARPES), we explored the electronic structure of the non-symmorphic crystals MSiS (M=Hf, Zr). Remarkably, by mapping out the band structure in the full 3D Brillouin Zone (BZ), we observed two sets of Dirac line-nodes in parallel with the kz-axis and their dispersions. Interestingly, along directions other than the line-nodes in the 3D BZ, the bulk degeneracy is lifted by spinorbit coupling (SOC) in both compounds with larger magnitude in HfSiS. Our work not only experimentally confirms a new Dirac line-node semimetal family protected by nonsymmorphic symmetry, but also helps understanding and further exploring the exotic properties as well as practical applications of the MSiS family of compounds.

The magnetocaloric effect was investigated in LaFe11.7Si1.3, which undergoes a first-order transition at ∼188 K from the ferromagnetic to paramagnetic state. The magnetic entropy change upon a field increase from 0 to 5 T is as large as 29 J/kg K (212 mJ/cm3 K). The adiabatic temperature change obtained via direct measurements reaches 4 K under a field change from 0 to 1.4 T. The large values of entropy change and adiabatic temperature change confirmed the large potential of present compound LaFe11.7Si1.3 as a magnetic refrigerant in the corresponding temperature range.

Two-dimensional optically active ZnO shells on polystyrene (PS) templates have been fabricated using a sputtering technique. Periodic ZnO hollow half-shell structure has been obtained by removing PS templates. It exhibits several anomalous dips in transmission spectra that have not been reported. The dips can be tuned up by changing the shell thickness and PS sphere size. The PL spectra confirm that the structure has enhanced defect emission of ZnO.