Upper critical fields and interface transparency in superconductor/ferromagnet bilayers

Abstract

Proximity effect in Nb/ Pd 0.86 Ni 0.14 , Nb/Cu 0.46 Ni 0.54 , and Nb/ Cu 0.42 Ni 0.58 bilayers has been studied in the presence of an external magnetic field. Upper critical field measurements, performed in parallel configuration, reveal a shift of the two-dimensional-three-dimensional crossover temperature, which we relate to the different interface transparencies of the three analyzed systems.

Giant coercivity enhancement and dimensional crossover of superconductivity in Co2FeSi-NbN nanoscale bilayers

“…Note that calculated d eff for pure NbN film is close to the actual thickness ( 35 nm) of the film, which confirms the reliability of the data. Similar behavior of dimensional crossover is seen in other systems of FSBs with soft ferromagnet where T C -T CR 1 K is reported 15 .The observation of a square hysteresis loop with very low coercivity (as shown below) in the normal state (T >T c ) suggests that the CFS layer is a single magnetic entity. In that case, the 4 Cooper pair electrons with opposite spins in the NbN layer will not diffuse into a fully spin polarized CFS layer, which makes the origin of the decrease in T c and d eff in FSB with respect to pure NbN a-priori unclear.…”

“…In addition, for both the samples H c2 (T) shows a linear behavior at T << T c and a nonlinear behavior at T < T c . We identify this result with a 2D-3D crossover, occurring at a characteristic temperature T CR , which has been frequently observed in S and S-F heterostructures [15][16][17] . At lower temperatures, when the coherence length perpendicular to the plane of the film (T) < d s (S-layer thickness) the film behaves like a 3D system.…”

“…The NbN thin films have been reported to show anisotropic behavior also due to the grain morphology 19 . Thus, we prefer to employ an anisotropic GL (Ginzburg Landau) model to describe the behavior of H c2// (T) in our films, which in the 3D regime ( (T) < d s ) is given by 20,15 : It is interesting to note that the values of T C -T CR for pure NbN and FSB are 0.2 and 1 K respectively. While the thickness of NbN is same in both the samples, the higher value of T C -T CR in FSB sample can be attributed to the reduction of the effective thickness (d eff ) of the NbN layer in FSB due to the proximity of the CFS layer.…”

“…The NbN thin films have been reported to show anisotropic behavior also due to the grain morphology 19 . Thus, we prefer to employ an anisotropic GL (Ginzburg Landau) model to describe the behavior of H c2// (T) in our films, which in the 3D regime ( (T) < d s ) is given by 20,15 :…”

Modulation of the properties of thin ferromagnetic films with an externally applied electric field in ferromagnetic/piezoelectric/ferromagnetic hybrids

“…For instance, the modulation of the properties of a superconductor (SC) by the exchange field (superconducting spin valve effect) and/or stray fields (superconducting magnetoresistance effect) provided by an adjacent ferromagnet (FM) has been studied in great detail both experimentally [1][2][3][4][5] and theoretically 6,7 in various versions of SC/FM hybrids. Another example comes from the field of exchange bias where the exchange coupling between a FM and an adjacent antiferromagnet is effective only in the limit of thin films since the cornerstone macroscopic parameter involved in this effect, the so-called exchange bias field, is inversely proportional to the thickness of the FM layer due to the limited penetration of the coupling field inside its interior.…”