We report on high-resolution terahertz spectroscopic studies of quantum spin dynamics in the quasi-one-dimensional Ising-like ferromagnet CoNb$_2$O$_6$ and antiferromagnet BaCo$_2$V$_2$O$_8$ as a function of an applied transverse magnetic field. In the ordered phases stabilized by inter-chain couplings, we reveal characteristics for confined spinon excitations, $E_8$ dynamical spectrum, and field-induced quantum phase transitions. The connections between these characteristic dynamical features are found in the field-dependent evolution of the excitation spectra.

Poly (3-hexylthiohene) (P3HT) has attracted much attention due to their chemical and thermal stability as well as their potential to be used as an active material in solar cells. Recently, bulk-heterojunction BHJ solar cell has been intensively developed due to its potential for high power conversion efficiency and low cost solar cells. Many studies have been done to understand the effect of PCBM to the morphology of the P3HT:PCBM blend and to performance of its solar cells. However, the clearly explanation about the effect of PCBM to the charge carrier dynamics in P3HT is not well understood yet. We have studied charge carrier dynamics in active material of solar cell P3HT:PCBM along and perpendicular to the chain by means of longitudinal field (LF) muon-spin-relaxation (μSR) method to elucidate the intra and inter-chain charge carrier in polymer hybrid P3HT:PCBM. We found the charge carrier transport changes from intra-chain to inter-chain diffusion. One dimensional intra-chain diffusion is observed in the samples at low temperatures below 10K, while three dimensional inter-chain is observed at high temperatures above 15K. This temperature is lower than that of P3HT only.

We report the effects of oxygen deficiency to the electronic and magnetic properties of SrCoO3 calculated using spin-polarized Density Functional Theory. The correlation effects of the Co 3d orbitals are considered explicitly using the effective Hubbard U eff parameter. The U eff consists of the subtraction between the U value of 3 eV to denote the Coulomb interaction and the Hund’s coupling parameter J of 0.95 eV. Our results show that the localized character of the Co 3d orbitals strongly depends on the oxygen content. The magnetic exchange interaction between two neighboring Co ions is therefore altered. As a consequence, a change of magnetic ground state using the same U eff value from ferromagnetic ordering in full oxygen content to antiferromagnetic ordering in SrCoO2.5 is obtained.

The dream to have multifunctional materials has triggered an intense study of multiferroicity,i.e.of materials in which magnetic and electric polarizations are simultaneously present and strongly coupled. Here we study TbMnO3, a perovskite manganite exhibiting multiferroicity. It has an incommensurate antiferromagnetic ordering transition at 41 K and a transition into a multiferroic spin spiral state at 26 K. In this study, Raman spectroscopy has been used to elucidate the nature of the excitations related to phase transitions. We show that the optical phonons in TbMnO3resemble the phonon characteristics typical for perovskite manganites, corresponding to MnO6octahedral vibrations. The appearance of a new low energy modes at 32 cm-1, 40 cm-1, and 63 cm-1observed below 41 K signifies the antiferromagentic ordering in TbMnO3. The 32 cm- 1and 63 cm-1are interpreted as spin ordering activated phonon while the 40 cm-1is interpreted as spin ordering induced splitting of Tb quasi doublet cystal field level.

Spinel material Cobalt Chromite (CoCr2O4) is a ferrimagnetic material with TC of about 93 K. This compound has attracted much attention due to the presence of electrical polarization which related to spiral magnetic transition at TS = 26 K. [Physical Review B, 70, 214434, 2004]. This spiral magnetic transition phenomena could be explored by experiment using Muon Spin Rotation, Relaxation, and Resonance (liSR) . Positive muon in liSR plays a role as a local magnetic probethus, we need to determine the muon stopping site information. In this study, we investigate the muon stopping site of CoCr2O4 with ferrimagnetic ground state using spin polarized Density Functional Theory implemented in Full-potential Linearized Augmented Plane Wave (FLAPW) method. The exchange-correlation effect was considered in the scheme of GGA+Ueff approximation. Based on the minimum energy of electrostatic potential, we obtain the muon stopping site around the three Oxygen ions in the tetrahedral site of Cobalt.