Due to its high electrical conductivity and excellent transmittance at terahertz frequencies, graphene is a promising candidate as transparent electrodes for terahertz devices. We demonstrate a liquid crystal based terahertz phase shifter with the graphene films as transparent electrodes. The maximum phase shift is 10.8 degree and the saturation voltage is 5 V with a 50 µm liquid crystal cell. The transmittance at terahertz frequencies and electrical conductivity depending on the number of graphene layer are also investigated. The proposed phase shifter provides a continuous tunability, fully electrical controllability, and low DC voltage operation.

Recent discovery of intrinsic ferromagnetism in two-dimension (2D) van der Waals (vdW) crystals has opened up a new arena for spintronics, raising an opportunity of achieving the tunable intrinsic 2D vdW magnetism. Here, we show that the magnetization and the magnetic anisotropy energy (MAE) of the few-layered Fe3GeTe2 (FGT) is strongly modulated by a femtosecond (fs) laser pulse. Upon increasing the fs laser excitation intensity, the saturation magnetization increases in an approximately linear way and the coercivity determined by the MAE, decreases monotonically, showing unambiguously the effect of the laser pulse on magnetic ordering. This effect observed at room temperature reveals the emergence of the lightdriven room-temperature (300K) ferromagnetism in the 2D vdW FGT as its intrinsic Curie temperature is ~ 200 K. The light-tunable ferromagnetism is attributed to the changes in the electronic structure due to the optical doping effect. Our findings pave a novel way to optically tune the 2D vdW magnetism and enhance the up to the room temperature, promoting spintronic applications at or above the room temperature.

We prepared 3 kinds of Li + -doped BaTiO 3 ceramics by the solid-state reaction method: (i) (Ba 1Àx Li x )TiO 3Àx/2 having A-site Li + , (ii) Ba(Ti 1Àx Li x )O 3À3x/2 having B-site Li + , and (iii) x/2 Li 2 CO 3 +BaTiO 3 mixed one, for which we investigated the stable site of Li. The density of all prepared ceramics is above 95%. The results show that the lattice structure, the grain size, and the electric properties of Li + -doped BaTiO 3 ceramics are dependent on Li + site. According to the increase in Li content, the cell volume of Ba 1Àx Li x TiO 3Àx/2 decreases, but that of BaTi 1Àx Li x O 3À3x/2increases. That of x/2Li 2 CO 3 +BaTiO 3 decreases by the small addition of Li, but increases by the large addition of Li. All Li + -doped ceramics show antiferroelectriclike double hysteresis loops. The shape of loops and the dielectric properties are also dependent on the Li site. We suggest that the role of oxygen vacancy accompanied by the Li-doping is important. By comparison with the results of 3 type ceramics, it is concluded that at x/2Li 2 CO 3 +BaTiO 3 ceramics, the Li + prefers to favorably substitute Ba 2+ at A site for the low concentration of Li but its location was changed to Ti 4+ site for the high concentration of Li.

Laser-induced spin dynamics of in-plane magnetized CoFeB films has been studied by using time-resolved magneto-optical Kerr effect measurements. While the effective demagnetization field shows little dependence on the pump laser fluence, the intrinsic damping constant has been found to be increased from 0.008 to 0.076 with the increase in the pump fluence from 2 mJ/cm2 to 20 mJ/cm2. This sharp enhancement has been shown to be transient and ascribed to the heating effect induced by the pump laser excitation, as the damping constant is almost unchanged when the pump-probe measurements are performed at a fixed pump fluence of 5 mJ/cm2 after irradiation by high power pump pulses.