Knight shift in superconducting vanadium

The Knight shift in metallic vanadium in the normal and superconducting states has been measured. In contrast to the previously obtained results, this shift appears to change after the transition to the superconducting state. The behavior of the Knight shift in the superconducting state in vanadium samples doped with iron impurities has been found to be different from that in the "pure" samples. As a possible explanation of the effect, the broadening of the peak of the density of states near the Fermi level due to the scattering of conduction electrons on the iron impurities and the earlier predicted impurity polarization shift of the NMR line are discussed. © 2008 Pleiades Publishing, Ltd

Experimental observation of the spin screening effect in superconductor/ferromagnet thin film heterostructures

When studying the nuclear magnetic resonance (NMR) of 51V nuclei in superconductor/ferromagnet thin film heterostructures, anomalous behavior of the NMR signal was observed. This effect was manifested as a systematic distortion of the high-field wing of the resonance line. We consider this to be the first experimental evidence for penetration of ferromagnetism into a superconductor. © 2010 Allerton Press, Inc

Spin screening effect in superconductor/ferromagnet thin film heterostructures studied using nuclear magnetic resonance

Using NMR spectroscopy of the V 51 nuclei in the superconducting state of Ni/V/Ni and Pd1-x Fex /V/ Pd1-x Fex trilayers we reported in a recent letter an experimental observation of the spin screening effect. This effect, which designates the formation of a spin polarization in the superconducting state, was predicted previously by Bergeret. Here, we extend our earlier experiments by varying the thickness of the superconducting V layer and by applying the magnetic field not only perpendicular to the film plane as in the previous experiments, but also in the parallel direction. For the latter geometry, which for experimental reasons is difficult to realize, the film is in the vortex-free state. This allows a direct quantitative comparison of the experimental screening effect as derived from a characteristic distortion of the high-field wing of the resonance line in the superconducting state and the theoretical model calculations. We derive a reasonable agreement between theory and experiment, confirming the spin screening effect in the superconductor. © 2009 The American Physical Society

EPR study of polycrystalline superconductors with YBa2Cu3O7 structure

Electron paramagnetic resonance (EPR) of Gd3+, Eu2+, and copper ions has been investigated in the high-Tc superconductor with YBa2Cu3O7-α structure. It has been established that the system is heterogeneous at 0.15≤δ≤0.5 and consists of metallic and dielectric regions. The former arises due to oxygen enrichment while the later due to oxygen deficiency. The integral of exchange interaction between Gd3+ localized moments and conduction electrons Jsf=0.016 eV has been determined from the normal state temperature dependence of Gd3+ EPR linewidth for metallic regions. Tc depression by gadolinium-localized moments for GdBa2Cu3O7-α was estimated to be ΔTc{reversed tilde equals}-2K. Anomalies in linewidth temperature dependence upon transition from the normal to the superconducting state have given information about the value and temperature behavior of the superconductor's energy gap. The model, which gives the opportunity to understand some peculiarities of the EPR signal for YBa2Cu3O7-α samples, is proposed in terms of several bottlenecked spinsubsystems: spin-liquid in CuO planes and Cu2+-O- and Cu2+-O2- fragments in CuO chains. © 1989 Plenum Publishing Corporation

Experimental observation of the spin screening effect in superconductor/ferromagnet thin film heterostructures

We have studied the nuclear magnetic resonance (NMR) of V51 nuclei in the superconductor/ferromagnet thin film heterostructures Pd1-xFex/V/Pd1-xFex and Ni/V/Ni in the normal and superconducting state. Whereas the position and shape of the NMR line in the normal state for the trilayers is identical to that observed in a single V layer, in the superconducting state the line shape definitely changes, developing a systematic distortion of the high-field wing of the resonance line. We consider this as the first experimental evidence for the penetration of ferromagnetism into the superconducting layer, a phenomenon which has been theoretically predicted recently and dubbed the spin screening effect. © 2009 The American Physical Society

Possible origin for oscillatory superconducting transition temperature in superconductor/ferromagnet multilayers

We have studied superconducting and magnetic properties of sputtered Fe/Nb/Fe trilayers. For a fixed Nb thickness and with changing Fe thickness, dFe, a nonmonotonic behavior of the superconducting transition temperature Tc was observed with a maximum at dFe ≈ 10 Å. The analysis of the magnetization data revealed that for dFFe ≤7 Å the Fe layer is nonmagnetic. The interpretation of the observed Tc behavior is attributed to the existence of this magnetically "dead" layer and the change of the interaction of the Cooper pairs with this layer at the onset of ferromagnetism for dFe ≥ 7 Å