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

1-Ethyl-2,3-dimethylimidazolium paramagnetic ionic liquids with 3D magnetic ordering in its solid state: synthesis, structure and magneto-structural correlations

Financial support from the Spanish Ministerio de Ciencia e Innovaci´on (Projects MAT2011-27573-C04) and Becas Iberoamericas J´ovenes Profesores Investigadores, 2015, Santander Universidades is acknowledged. The authors gratefully acknowledge the MALTA Consolider Ingenio 2010 (Ref. CSD2007-00045). IH acknowledges funding from the EU FP7 (Marie Curie-CIG 303535)

Nanoflowers Versus Magnetosomes Comparison Between Two Promising Candidates for Magnetic Hyperthermia Therapy

Magnetic Fluid Hyperthermia mediated by iron oxide nanoparticles is one of the most promising therapies for cancer treatment. Among the different candidates, magnetite and maghemite nanoparticles have revealed to be some of the most promising candidates due to both their performance and their biocompatibility. Nonetheless, up to date, the literature comparing the heating efficiency of magnetite and maghemite nanoparticles of similar size is scarce. To fill this gap, here we provide a comparison between commercial Synomag Nanoflowers pure maghemite and bacterial magnetosomes pure magnetite synthesized by the magnetotactic bacterium Magnetospirillum gryphiswaldense of amp; 10216;D amp; 10217; amp; 8776; 40 45 nm. Both types of nanoparticles exhibit a high degree of crystallinity and an excellent degree of chemical purity and stability. The structural and magnetic properties in both nanoparticle ensembles have been studied by means of X Ray Diffraction, Transmission Electron Microscopy, X Ray Absorption Spectroscopy, and SQUID magnetometry. The heating efficiency has been analyzed in both systems using AC magnetometry at several field amplitudes 0 88 mT and frequencies 130, 300, and 530 kH

Magnetic and nuclear structure of the perovskite like oxides (LaBi)0.7Ca 0.3MnO3

Progressive substitution of La by Bi in the mixed oxides (LaBi)(0.7)Ca0.3MnO3 leads to great changes in the magnetic and transport properties of these compounds. From neutron diffraction experiments performed at D1B and D2B apparatus in the ILL, we have observed changes in the magnetic structure from ferromagnetic La0.65Bi0.05Ca0.3MnO3 to antiferro Bi0.7Ca0.3MnO3. The intermediate compounds show antiferromagnetism in a crystalline plane and ferromagnetism in the perpendicular direction. The distance Bi-O turns out to be shorter than the La-O due to the covalent character of the former. This can explain the increasing localization of the 3d electrons of Mn atoms and the insulating character of Bi0.7Ca0.3MnO3

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