Thermal expansion of CaFe2As2: effect of cobalt doping and post-growth thermal treatment

We report thermal expansion measurements on Ca(Fe_(1-x)Co_x)_2As_2 single crystals with different thermal treatment, with samples chosen to represent four different ground states observed in this family. For all samples thermal expansion is anisotropic with different signs of the in-plane and c-axis thermal expansion coefficients in the high temperature, tetragonal phase. The features in thermal expansion associated with the phase transitions are of opposite signs as well, pointing to a different response of transition temperatures to the in-plane and the c-axis stress. These features, and consequently the inferred pressure derivatives, are very large, clearly and substantially exceeding those in the Ba(Fe_(1-x)Co_x)_2As_2 family. For all transitions the c-axis response is dominant

Combined effects of transition metal (Ni and Rh) substitution and annealing/quenching on physical properties of CaFe2_{2}As2_{2}

We performed systematic studies of the combined effects of annealing/quenching temperature ({\itshape T}$_{A/Q}$) and T = Ni, Rh substitution ({\itshape x}) on the physical properties of Ca(Fe$_{1-x}$T$_{x}$)$_{2}$As$_{2}$. We constructed two-dimensional, {\itshape T}$_{A/Q}$-{\itshape x} phase diagrams for the low-temperature states for both substitutions to map out the relations between ground states and compared them with that of Co-substitution. Ni-substitution, which brings one more extra electron per substituted atom and suppresses the {\itshape c}-lattice parameter at roughly the same rate as Co-substitution, leads to a similar parameter range of antiferromagnetic/orthorhombic in the {\itshape T}$_{A/Q}$-{\itshape x} space as that found for Co-substitution, but has the parameter range for superconductivity shrunk (roughly by a factor of two). This result is similar to what is found when Co- and Ni-substituted BaFe$_{2}$As$_{2}$ are compared. On the other hand, Rh-substitution, which brings the same amount of extra electrons as does Co-substitution, but suppresses the {\itshape c}-lattice parameter more rapidly, has a different phase diagram. The collapsed tetragonal phase exists much more pervasively, to the exclusion of the normal, paramagnetic, tetragonal phase. The range of antiferromagnetic/orthorhombic phase space is noticeably reduced, and the superconducting region is substantially suppressed, essentially truncated by the collapsed tetragonal phase. In addition, we found that whereas for Co-substitution there was no difference between phase diagrams for samples annealed for one or seven days, for Ni- and Rh- substitutions a second, reversible, effect of annealing was revealed by seven-day anneals

Boron isotope effect in single crystals of ErNi2_2B2_2C superconductor

The influence of local moment magnetism on the boron isotope effect of T$_c$ was studied on single crystals of ErNi$_2$B$_2$C. Values of the partial isotope effect exponent of $\alpha_B$=0.10$\pm$0.02 and $\alpha_B$=0.10$\pm$0.04 were obtained based on two different criteria applied to extract $T_c$. No significant change in the partial isotope effect exponent compared to the ones obtained for LuNi$_2$B$_2$C was observed. Based on this result we conclude that pair-breaking due to the Er local magnetic moment appears to have no detectable influence on boron isotope effect of T$_c$.Comment: 7 pages, 3 figure

Combined effects of post-growth thermal treatment and chemical substitution on physical properties of CaFe2 As2

This thesis summarizes experimental work using process of postgrowth thermal treatment and chemical substitution as tuning parameters in the study of physical properties of CaFe2As2. Details of sample preparation and characterization are given as well as various phase diagrams

Characterization and antitumor activity of camptothecin from endophytic fungus Fusarium solani isolated from Camptotheca acuminate

Background: Camptothecin (CPT) is a potent drug against cancers, originally from plants. The endophytic fungi could produce the secondary metabolite same as the host and is used as medicine.Objectives: The aim of this paper was to investigate an endophytic fungal CPT with anti-neoplastic activity.Methods: Endophytic fungi were isolated from Camptotheca acuminata in China. CPT from strain S-019 was characterized by TLC, HPLC and EI-MS analysis. Anti-tumor activity of fungal CPT was detected by MTT and fluorescent dye methods using Vero and PC-3 cells.Results: A total of 94 endophytic fungi strains were isolated from tissues of C. acuminata and 16 fungi strains displayed cytotoxic activity on Vero or PC3 cells. Of which, the fungal strain S-019, classified as Fusarium solani, displayed impressive cytotoxic activity on cancer cells and was found to produce CPT by analysis of TLC, HPLC and EI-MS methods. Bioassay studies confirmed that the fungi CPT had potent cytotoxicity on Vero cells and induced apoptosis of Vero cells.Conclusion: The endophytic fungi from camptotheca trees are a reliable source for natural anticancer compounds. The endophytic fungi could produce CPT same as plant. The fungal CPT exhibited effective activity at inhibiting cell growth and inducing apoptosis on Vero cells.Keywords: Endophytic fungi, camptothecin, anti-tumor, Camptotheca acuminat