Structural, magnetic and transport properties of Ni-Fe-Al alloys

Melt spun ribbons (MSR) of the Ni55Fe20Al25 alloy exhibit a first-order martensitic transition (MT) in the vicinity of a second-order ferromagnetic-to-paramagnetic phase transition. Contrasted with a sharp, complete and thermoelastic MT in MSR, a partial, sluggish and non-thermoelastic MT occurs in annealed Ni55Fe20Al25 alloy that possesses a much higher degree of atomic order. However, the annealed samples have stronger local magnetocrystalline anisotropy and higher Curie temperature (TC) than MSR. Negative magnetoresistance, Δρ|/ρ, is two times larger in MSR than in the annealed case. Δρ|/ρvs. H isotherms in MSR change curvature from concave-upwards to concave-downwards as the temperature is raised through TC whereas concave-downward curvature persists over the entire temperature range in the annealed counterpart

Exchange-enhanced spin fluctuations in a new unconventional superconductor

Experimental evidence for the presence of antiferromagnetic spin fluctuations (ASF) in LaAg1-cMnc alloys is presented. In view of the present results, the most likely mechanism for electron pairing seems to be the one mediated by ASF

Antiferromagnetic-spin-fluctuation-mediated pairing as a likely mechanism for unconventional superconductivity in LaAg<SUB>1-c</SUB>Mn<SUB>c</SUB> alloys

Electrical resistivity, ac magnetic susceptibility, specific heat, dc magnetization, and dc magnetic susceptibility of superconducting LaAg1-cMnc alloys with c=0.0, 0.025, 0.05. 0.1, 0.2, and 0.3 have been measured in the temperature range of 0.35 K&#8804;T&#8804;300 K at external magnetic fields ranging from 0 to 90 kOe with a view to unravel the exact nature of the superconducting ground state. In these alloys, each Mn atom carries a magnetic moment of &#8773;4&#956; B. A comparison of the results of these investigations with the predictions of the existing theoretical models permits us to make a number of interesting observations that include the following. The intermetallic compound LaAg is an archetypal Bardeen-Cooper-Schrieffer (BCS) spin-singlet isotropic even-parity s-wave superconductor with a superconducting transition temperature of Tc=0.97 K. At low solute concentrations of c&#8776;0.03, Mn substitutes for La at the La sublattice sites in the LaAg parent compound and Tc suddenly drop from 0.97 to temperatures below 0.35 K, reflecting thereby the destruction of conventional phonon-mediated s-wave superconductivity of the LaAg host by pair-breaking magnetic (Mn) impurities. At a threshold concentration of Mn, c&#8773;0.05 (which corresponds to the antiferromagnetic instability/critical phase boundary in the magnetic phase diagram), superconducting gap opens up, Tc abruptly shoots up to 5 K, and unconventional superconductivity sets in at ambient pressure for T&#8804;Tc. Beyond this threshold concentration, Mn has exclusive site pre- ference for Ag at the Ag sublattice sites in LaAg and Tc increases from 5 to 6 K. The unconventional nature of superconductivity at these solute concentrations is signaled by strong departures from the BCS predictions. We present ample experimental evidence that favors antiferromagnetic-spin-fluctuation-mediated pairing as the most likely mechanism for the unconventional (d-wave) superconductivity observed in LaAg1-cMnc alloys with c&#8805;0.05

Unconventional superconductivity in LaAg<SUB>1-x</SUB>Mn<SUB>x</SUB>: relevance of spin-fluctuation-mediated pairing

We provide experimental evidence for unconventional superconductivity in a newly synthesized three-dimensional nearly antiferromagnetic metal, LaAg1-xMnx, and report results that indicate that the antiferromagnetic spin-fluctuation-mediated pairing may have a direct bearing on this phenomenon. Compared to the heavy-fermion systems, the superconducting transition temperature is nearly 10 times higher, superconductivity is robust against impurities and the specific-heat anomaly associated with the superconducting transition is extremely weak, or even absent. Our results are consistent with certain previously reported theoretical criteria for observing antiferromagnetic spin-fluctuation-mediated superconductivity at elevated temperatures

Increased expression of intercellular adhesion molecule 1, CD11/CD18 cell surface adhesion glycoproteins and alpha 4 beta 1 integrin in a rat model of chronic interstitial lung fibrosis

The expression of the intercellular adhesion molecule 1 (ICAM-1), and the integrins CD49, CD11b/c, and CD11a(LFA-1 alpha chain) was analyzed in an experimental model of pulmonary fibrosis. Adult rats were exposed to 75% oxygen during 10 weeks, and to 2.0 mg/kg of paraquat twice weekly. Rats were sacrificed at 2 days, and at 2 and 10 weeks after the first injection of paraquat. Lungs were fixed in 4% paraformaldehyde and used for histology and immunohistochemistry. At 2 days the lungs showed a diffuse inflammation composed of a mixed polymorphonuclear and mononuclear cell infiltrate. Afterwards, the inflammatory process was predominantly mononuclear, and an increasing fibroblast proliferation was observed. Early inflammatory events (48 h) correlated with a moderate increased expression of ICAM-1, LFA, and CD11b/c in epithelial cells as well as a pronounced expression of ICAM-1 and CD11b/c in macrophages. At 2 and 10 weeks, there was a progressive increased expression of CD11b/c and ICAM-1 by macrophages, as well as of LFA in epithelial cells, and of ICAM-1 and CD49 by epithelial and interstitial cells. Lymphocytes showed a slight increased expression of LFA at 2 weeks, and of CD49 at 2 and 10 weeks. These results suggest that macrophages expressing ICAM-1, CD11b/c, and CD49 are involved in the earlier and late phases of the disease whereas fibroblast and epithelial cells expressing ICAM-1 and CD49 might play a role in the cell interactions involved in the fibrotic phase

Electrical resistivity of Fe-Zr glasses from 4.2 to 1100 K

The results of electrical resistivity &#961;(T) measurements on Fe-rich Fe-Zr glasses in a wide temperature range are presented. The &#961;(T) data show minima at temperatures close to the Curie temperature (Tc). A change of slope around 600 K, resembling the behaviour of the Fe-Zr-Cu-B nanocrystalline alloy, is caused by the crystallisation process. An evaluation of various contributions to electrical resistivity reveals that the contribution due to the magnetic scattering is masked by electron-phonon, quantum interference and pseudo-Kondo scattering processes

Spin fluctuation effects in, and quantum corrections to, the conductivity of Fe<SUB>90+x</SUB>Zr<SUB>10-x</SUB> (x=0, 1) metallic glasses

Magnetization, M(H,T), and electrical resistivity, &#961;(T), measurements on amorphous Fe90+xZr10-x (x = 0, 1) alloys indicate that spin wave excitations, single-particle excitations plus local spin-density fluctuations (LSF) and LSF [Kondo spin-flip scattering, enhanced electron-electron interaction effects and weak localization as well as LSF effects] dominantly contribute to M(o, T) [&#961;(T)] at low, intermediate and high temperatures