High-pressure synthesis of new filled skutterudite compounds SrT4As12 (T = Fe, Ru, Os)

We have succeeded in synthesizing samples of new filled skutterudite compounds SrT 4As12 (T = Fe, Ru, and Os) using a high-pressure synthesis technique. These compounds have lattice constants of 8.351, 8.521, and 8.561 Å, respectively. The physical properties of the compounds are reported for the first time. The temperature dependences of the electrical resistivity for SrT 4As12 (T = Fe, Ru, and Os) exhibit metallic behaviors. The electrical resistivity and magnetic measurements indicates that SrOs4As12 is a new superconductor with a transition temperature of 4.8 K. A broad maximum of magnetic susceptibility at around 50 K and a large electronic specific heat coefficient of 58 mJ mol−1 K−2 suggest that SrFe4As12 is a nearly ferromagnetic metal with spin fluctuations of Fe 3d electrons

High-pressure Synthesis and Bulk Modulus of Non-centrosymmetric Superconductor Mo3Al2C

Mo3Al2C is a superconductor without inversion symmetry (the transition temperature T C ~ 9K). We have succeeded in preparing high-quality samples of Mo3Al2C using the high-pressure synthesis technique. The samples were characterized by powder x-ray diffraction (XRD) analysis. Furthermore, powder XRD patterns for the samples with synchrotron radiation have been studied under high pressures up to around 10 GPa and the volume versus pressure curve for the compound has been investigated. A bulk modulus was estimated to be 221 GPa

The structural, transport, and magnetic properties of Yb-filled skutterudites YbyFexCo4−xSb12 synthesized under high pressure

The effects of Fe-substitution on partially Yb filled skutterudites YbyFexCo4-xSb12 are presented from the viewpoint of crystal structure and thermoelectric, magnetic, and transport properties. A series of polycrystalline n-type YbyFexCo4-xSb12 (0.21 ≤ y ≤ 0.47, 0 ≤ x ≤ 0.76) samples were prepared using a high-pressure and high-temperature method. X-ray diffraction data suggest that all the compounds are high-purity skutterudites. For the YbyFexCo4-xSb12 with Yb content higher than 0.29 and Fe content lower than 1, the lattice constant shows a saturated behavior despite the change in the Yb/Fe content. Rietveld refinement based on the synchrotron radiation X-ray data implies that the rectangular Sb4 ring is transformed into square with increasing Yb content and/or Fe substitution content. The Yb valence gradually decreases as the Fe content increases from magnetic susceptibility analysis. According to the specific heat analysis, higher Yb filling benefits the lower Debye temperature while the Fe substitution leads to an increased Debye temperature. The Einstein temperature decreased with increasing Yb filling fraction, but Fe substitution for the Co site does not change the Einstein temperature further. Fe-substitution causes the reduction of total thermal conductivity κ, which mainly originates from the decrease of electron thermal conductivity contribution. The resistivity, Seebeck coefficient, thermal conductivity, and figure of merit (ZT) were effectively tuned due to the optimization of the carrier concentration. At the same carrier concentration, the hall mobility was decreased by Fe substitution. The proper Fe substitution content (0.2 in Yb0.25Fe0.2Co3.8Sb12) can result in a relatively high effective mass

High-field magnetization and magnetic phase transition in CeOs2Al10

We have studied the magnetization of CeOs2Al10 in high magnetic fields up to 55 T for H // a and constructed the magnetic phase diagram for H // a. The magnetization curve shows a concave H dependence below T_max \sim40 K which is higher than the transition temperature T_0 \sim29 K. The magnetic susceptibility along the a-axis shows a smooth and continuous decrease down to \sim20 K below T_max \sim40 K without showing an anomaly at T_0. From these two results, a Kondo singlet is formed below T_max and coexists with the antiferro magnetic order below T_0. We also propose that the larger suppression of the spin degrees of freedom along the a-axis than along the c-axis below T_max is associated with the origin of the antiferro magnetic component.Comment: 4 pages, 4 figures, to appear in Phys. Rev. B, Rapid Commu

Suppression of ferromagnetic spin fluctuations in the filled skutterudite superconductor SrOs4As12 revealed by As-75 NMR-NQR measurements

Motivated by the recent observation of ferromagnetic spin correlations in the filled skutterudite SrFe4As12 [Q.-P. Ding et al., Phys. Rev. B 98, 155149 (2018)], we have carried out As-75 nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements to investigate the role of magnetic fluctuations in the newly discovered isostructural superconductor SrOs4As12 with a superconducting transition temperature of T-c similar to 4.8 K. Knight shift K determined by the NQR spectrum under a small magnetic field (<= 0.5 T) is nearly independent of temperature, consistent with the temperature dependence of the magnetic susceptibility. The nuclear spin-lattice relaxation rate divided by temperature, 1/T1T, is nearly independent of temperature above similar to 50 K and increases slightly with decreasing temperature below the temperature. The temperature dependence is reasonably explained by a simple model where a flat band structure with a small ledge near the Fermi energy is assumed. By comparing the present NMR data with those in SrFe4As12, we found that the values of vertical bar K vertical bar and 1/T1T in SrOs4As12 are smaller than those in SrFe4As12, indicating no obvious ferromagnetic spin correlations in SrOs4As12. From the temperature dependence of 1/T-1 in the superconducting state, an s-wave superconductivity is realized

High-field magnetization and magnetic phase transition in CeOs2Al10

We have studied the magnetization of CeOs2Al10 in high magnetic fields up to 55 T for H // a and constructed the magnetic phase diagram for H // a. The magnetization curve shows a concave H dependence below T_max \sim40 K which is higher than the transition temperature T_0 \sim29 K. The magnetic susceptibility along the a-axis shows a smooth and continuous decrease down to \sim20 K below T_max \sim40 K without showing an anomaly at T_0. From these two results, a Kondo singlet is formed below T_max and coexists with the antiferro magnetic order below T_0. We also propose that the larger suppression of the spin degrees of freedom along the a-axis than along the c-axis below T_max is associated with the origin of the antiferro magnetic component.Comment: 4 pages, 4 figures, to appear in Phys. Rev. B, Rapid Commu

Inhibition of Uterine Sarcoma Cell Growth through Suppression of Endogenous Tyrosine Kinase B Signaling

Uterine leiomyosarcoma is an aggressive tumor typically found at advanced stages due to difficulties with early diagnosis. Because uterine leiomyosarcoma is resistant to conventional radiation and chemotherapy, the development of more potent medical therapeutics is anticipated. Using quantitative real-time RT-PCR and immunostaining, we found the expression of brain-derived neurotrophic factor (BDNF) and neurotropin-4/5, together with their receptor, tyrosine kinase B (TrkB), in different uterine sarcoma cell lines and primary tumor samples from uterine leiomyosarcoma patients. We noted that levels of BDNF were more abundant than those of neurotropin-4/5. Moreover, the expression of TrkB and its ligands was elevated in a multidrug-resistant cell line and samples obtained from patients with leiomyosarcoma. In cultured uterine sarcoma cells, inhibition of endogenous TrkB signaling by treatment with either the soluble TrkB ectodomain or the Trk receptor inhibitor, K252a, suppressed cell proliferation and increased apoptosis based on cell viability and proliferation, in situ terminal deoxynucleotidyl transferase-mediated 2\u27-deoxyuridine 5\u27-triphosphate nick end-labeling and caspase-3/7 assays, whereas an inactive plasma membrane nonpermeable K252b was ineffective. Correspondingly, treatment with exogenous BDNF increased cell proliferation. In in vivo studies in athymic nude mice bearing multidrug-resistant uterine sarcoma cell tumors, we demonstrate suppression of tumor growth by treatment with K252a, but not K252b, as reflected by decreased cell proliferation and increased levels of apoptosis and caspase-3/7 activities without obvious side effects. Our findings indicated that endogenous signaling of the TrkB pathway contributed to uterine sarcoma cell growth, and inhibition of TrkB signaling in these tumors could provide a novel medical therapy for patients with uterine sarcomas

Enhanced thermoelectric performance of optimized Yb-filled and Fe-substituted skutterudite compounds Yb0.6FexCo4−xSb12

Optimized Yb-filled Fe-substituted skutterudites Yb0.6Fe x Co4? x Sb12 (x = 0, 0.5, and 1.0) were synthesized using a high-pressure technique. The samples were characterized by powder X-ray diffraction (XRD) analysis and electron probe microanalysis (EPMA). The thermoelectric transport properties of the samples such as Seebeck coefficient, electrical conductivity, carrier concentration, and thermal conductivity were studied in the temperature range of 2?300 K. With 1/8 Fe substitution for the Co site (x = 0.5), the Seebeck coefficient and thermal conductivity were obviously optimized. Carrier concentration analysis indicates that proper Fe substitution can effectively compensate for the excess electrons and optimize the electric transport properties. The reduction in the total thermal conductivity κ could be mainly caused by the reduction in electron contribution to κ. Compared with an only-Yb-filled compound, a 26% improved figure of merit ZT was achieved at 300 K at the Fe substitution ratio x = 0.5 (ZT = 0.11). This result confirms that Fe substitution on the Co site is an effective approach to tuning and optimizing the thermoelectric properties of CoSb3-based skutterudites

Filled skutterudite superconductor CaOs4P12 prepared by high-pressure synthesis

In this paper, we report the transport, thermodynamic, and superconducting properties of a new filled skutterudite CaOs4P12 synthesized under high pressure and high temperature. The electrical resistivity of 3.4–4.8 mΩcm, carrier concentration of 3.8–6.1 × 1020cm−3 , and positive Hall coefficient suggest that CaOs4P12 is a semimetal with hole carriers. An anomaly due to low-energy optical modes corresponding to an Einstein temperature of 150 K was observed in the specific heat. Resistivity, dc magnetic susceptibility, and specific heat measurements indicate bulk superconductivity below 2.5 K. The specific heat anomaly at Tc, ∆C/γTc ≈ 1.4, is in agreement with the BardeenCooper-Schrieffer (BCS) value of 1.43. The electron-phonon coupling constant λep is estimated to be 0.47. CaOs4P12 is classified as a BCS-type, weakly coupled type-II superconductor with an upper critical field of Hc2 ≈ 22 kOe and Ginzburg-Landau coherence length of ξ ≈ 12 nm