The magnetoresistance of epitaxial Nd0.7Sr0.3MnOδ thin films has been studied. A giant magnetoresistance, with more than 4 orders of magnitude change in resistance (−ΔR/RH≳106%), was obtained at ∼60 K and a magnetic field of 8 T. This giant magnetoresistance (GMR) ratio is about one order of magnitude larger than the highest value reported previously which was observed in La–Ca–Mn–O film. We have also obtained a large GMR ratio with −ΔR/RH≳3000% for H=5 T in an in situ Nd0.7Sr0.3MnOδ thin film, a much larger effect than the previous results in doped manganese oxide films in which a large GMR ratio was obtained only in postannealed samples. Our results also show that the GMR effect in these films can be strongly influenced by the thin-film preparation conditions.

We study optical, structural, and surface anchoring properties of thermotropic nematic bent-core material A131. The focus is on the features associated with orientational order as the material has been reported to exhibit not only the usual uniaxial nematic but also the biaxial nematic phase. We demonstrate that A131 experiences a surface anchoring transition from a perpendicular to tilted alignment when the temperature decreases. The features of the tilted state are consistent with surface-induced birefringence associated with smectic layering near the surface and a molecular tilt that changes along the normal to the substrates. The surface-induced birefringence is reduced to zero by a modest electric field that establishes a uniform uniaxial nematic state. Both refractive and absorptive optical properties of A131 are consistent with the uniaxial order. We found no evidence of the "polycrystalline" biaxial behavior in the cells placed in crossed electric and magnetic fields. We observe stable topological point defects (boojums and hedgehogs) and nonsingular "escaped" disclinations pertinent only to the uniaxial order. Finally, freely suspended films of A131 show uniaxial nematic and smectic textures; a decrease in the film thickness expands the temperature range of stability of smectic textures, supporting the idea of surface-induced smectic layering. Our conclusion is that A131 features only a uniaxial nematic phase and that the apparent biaxiality is caused by subtle surface effects rather than by the bulk biaxial phase.

Novel regioisomeric alkylated-naphthalene liquids were designed and synthesized. In the solvent-free liquid state, 1-alkyloxy regioisomers showed excimeric luminescence, whereas 2-alkyloxy analogues exhibited monomer-rich luminescence features. Correlations among the molecular structures and the photophysical, calorimetric, and rheological properties are presented, demonstrating the impact of regioisomerism on the alkylated-chromophore liquid systems.

We present studies of chiral nematic liquid crystals composed of flexible dimer molecules subject to large dc magnetic fields between 0 and 31 T. We observe that these fields lead to selective reflection of light depending on temperature and magnetic field. The band of reflected wavelengths can be tuned from ultraviolet to beyond the IR-C band. A similar effect induced by electric fields has been presented previously, and was explained by a field-induced oblique-heliconical director deformation in accordance with early theoretical predictions. The use of magnetic field here instead of electric field allows precise measurements of some material constants and holds promise for wireless tuning of selective reflection.

Lasing in induced cholesteric liquid crystal (CLC) containing highly photosensitive azo chiral dopant (ChD) and pyrromethene laser dye was investigated. Due to the absence of excitation energy transfer from the dye molecules to the molecules of ChD in such a system, a low lasing threshold was achieved. When using violet and green lightemitting diodes, reversible frequency tuning was obtained in the range of about 30 nm with a tuning time 1-2 orders of magnitude smaller than in conventional CLC laser systems based on azo and azoxy photosensitive compounds. Further increase of the intensity of the excitation light by using a green laser pointer allowed us to achieve a record phototuning speed (∼21 nm in 148 ms).Distributed feedback (DFB) lasers based on dye-doped cholesteric liquid crystals (CLCs) were first established in 1980 [1]. Based on the characteristics reported to date, such as threshold excitation intensity, linewidth, and energy efficiency, they can actually be used for development of high-brightness laser displays [2]. Perfection of components for these devices, e.g., development of dye activators with minimal triplet-triplet absorption, CLCs with a high melting point and temperature-independent pitch length make it possible to produce lasing under continuous excitation [3].Since the creation of the DFB laser, a practical problem is to develop a method for tuning of its frequency, which would provide high speed and reversibility of this process. In practice, the tuning is achieved by changing the pitch of the CLC's helix, impacting on it by mechanical, thermal, electrical, or light factors [4]. The last process, photocontrolling of helical pitch, is of particular interest due to the remote, spatial, and temporal activation advantages of light stimulus. The method of tuning the lasing frequency based on this effect, which more generally is seen as a method of controlling light by means of light, is considered the most promising in terms of the above requirements of the process of tuning [4].Variation of the helical pitch under the influence of light is due to a change in the helical twisting power of chiral molecular switches in CLCs as a result of the photoconversion of molecules of the chiral dopant (ChD) [5-9], or liquid crystal host [10][11][12][13]. Often, these phototransformations (photo-Fries reaction, photolysis reaction, etc.) cause irreversible changes in the helical pitch [5,6]. However, some phototransformations (such as a trans-cis isomerization of azo and azoxy compounds) are generally reversible; the photoexcited cis isomers of such molecules relax to initial trans form when heated or exposed to light of a different wavelength. The case of cis-trans photoisomerization is the most interesting, because it allows one to change the frequency of lasing in two opposite directions by means of the same, quite a technological factor, i.e., light.Note that the efficiency of trans-cis and cis-trans photoisomerization and, consequently, the efficiency of lasing frequency tuning, depends on a number o...