[en] The ac susceptibility of single crystals of Ni₄ single-molecule magnets is measured by a compensation measurement setup. The magnetic relaxation time calculated from the peak of the out-phase component of the susceptibility fits the Arrhenius law well and gives an effective spin-flipping energy barrier of U_eff = 7.2 K. This value is far below the classical activation energy barrier of U = 14 K, whereas it is close to the energy gap between the S_z = ±4 and S_z = ±3 doublets, which indicates that quantum tunneling between the S_z = 3 and S_z = −3 states plays a key role in the magnetic relaxation. Therefore the relaxation process combines thermal activation and quantum tunneling. Also we deduce that the blocking temperature of Ni₄ single-molecule magnets is lower than 0.3 K by extrapolating the relaxation time plot, which ensures that this single-molecule magnet material enters a long-range magnetic ordered state instead of a spin glass state at 0.91 K. (condensed matter: electronicstructure, electrical, magnetic, and opticalproperties)

[en] We study the photodarkening effect in a double clad ytterbium-doped silica fiber fabricated by modified chemical vapor deposition and solution doping. A common measurement technology for photodarkening is used to study the photodarkening-induced absorption spectra. We present a fast and simple method to observe the PD effect by measurement of the fluorescence spectra. The method proposed here can be used to observe the influence for a short time, and thus reduces the requirements of system stability and heat management. It is obtained that under the condition of 45.5% Yb ion inversion level, photodarkening-induced excessive loss at an equilibrium state is above 4.5dB/m and florescence intensity degradation is above 10% after 500min pumping at 1041 nm for the home-made normal Yb/Al co-doped silica fiber

[en] In this work, hydrothermal synthesis and ceramic sintering process were applied to fabricate (1−x)Pb(Zr_0.52Ti_0.48)O₃−(x)CoFe₂O₄ (PZT–CFO) (x=0.20, 0.35, and 0.50) magnetoelectric (ME) composites. The X-ray diffraction (XRD) studies revealed that no chemical reaction occurred between individual PZT and CFO phases and confirmed the manifestation of PZT and CFO phases within the ME composite. Scanning electron microscopy (SEM) was used to investigate the microstructure and connectivity scheme in the ME composites. The dielectric constant (ε) and loss tangent (tan δ) were determined as functions of frequency and temperature for all the composites prepared. The polarization–electric field (P–E) and magnetization–magnetic field (M–H) hysteresis loops obtained indicate that both ferroelectric and ferromagnetic properties coexist in the ME composites prepared. The direct (DME) and converse magnetoelectric effects (CME) were measured only for the PZT–CFO20 (20 mol% CoFe₂O₄) composite sintered at 1100 °C for 4 h. The maximum values of ME voltage coefficient α_ME(dE/dH) and ME susceptibility coefficient α_me (dH/dE) were 226 mV cm⁻¹ Oe⁻¹ at frequency of 75.1 kHz and 1.15×10⁻⁸ s/m at frequency of 66.8 kHz, respectively. - Highlights: • PZT–CFO composite was prepared by hydrothermal method and ceramic sintering process. • Effect of CoFe₂O₄ content on the electrical and magnetic properties is studied. • CoFe₂O₄ particles are uniformly distributed in the PZT matrix. • P–E and M–H hysteresis loops confirm room-temperature multiferroic characteristics. • T_m shifts to higher values with the increase in the measurement frequency