Magnetic and superconducting phase diagram of Nb/Gd/Nb trilayers

Abstract

We report on a study of the structural, magnetic and superconducting properties of Nb(25nm)/Gd(d f )/Nb(25nm) hybrid structures of a superconductor/ ferromagnet (S/F) type. The structural characterization of the samples, including careful determination of the layer thickness, was performed using neutron and X-ray scattering with the aid of depth sensitive mass-spectrometry. The magnetization of the samples was determined by SQUID magnetometry and polarized neutron reflectometry and the presence of magnetic ordering for all samples down to the thinnest Gd(0.8nm) layer was shown. The analysis of the neutron spin asymmetry allowed us to prove the absence of magnetically dead layers in junctions with Gd interlayer thickness larger than one monolayer. The measured dependence of the superconducting transition temperature Tc(d f ) has a damped oscillatory behavior with well defined positions of the minimum at d f =3nm and the following maximum at d f =4nm; the behavior, which is in qualitative agreement with the prior work (J.S. Jiang et al, PRB 54, 6119). The analysis of the Tc(d f ) dependence based on Usadel equations showed that the observed minimum at d f =3nm can be described by the so called "0" to "π" phase transition of highly transparent S/F interfaces with the superconducting correlation length ξ f ≈ 4nm in Gd. This penetration length is several times higher than for strong ferromagnets like Fe, Co or Ni, simplifying thus preparation of S/F structures with d f ∼ ξ f which are of topical interest in superconducting spintronics.

Magnetic proximity effect in Nb/Gd superlattices seen by neutron reflectometry

“…Thus AF alignment or any other modification of the magnetic period can be excluded in our structure. Moreover in our previous study of Nb(25nm)/Gd(d F )/Nb(25nm) trilayers we did not observe any statistically significant change of the spin asymmetry below T c [30]. All these observations point to an electrodynamical origin of the effect.…”

Proximity effect in [Nb(1.5 nm)/Fe(x)]10/Nb(50 nm) superconductor/ferromagnet heterostructures

“…From H c2 (0) we can estimate the superconducting correlation length ξ S = 12 nm. We note that 2D superconductivity was reported earlier for various structures with Nb layer thicknesses of 100 nm or less [5,33,35,36,41].…”

“…Superconductor(S)/ferromagnet(F) heterostructures are intensively studied systems, which are interesting for fundamental physics due to a big number of predicted and detected phenom-ena such as the appearance of non-uniform superconducting states (see reviews [1][2][3]). Among these phenomena are π-Josephson junctions [4][5][6][7] with a π-phase difference of super-conducting correlations between two neighboring interfaces, long-range triplet superconductivity [8][9][10][11][12][13][14][15][16] generated in S/F systems with a non-collinear (NC) magnetic configuration of the F system, and re-entrant superconductivity as evidence of nonuniform LOFF-states [17][18][19][20]. Apart from the interest in basic science, the proximity effect in S/F structures has great technological importance for the creation of spintronics devices, where the transport properties of the structure are controlled via the manipulation of the magnetic order in the F subsystem [21][22][23][24][25][26].…”

Spin transport and Spin Tunnelling Magneto-Resistance (STMR) of F|NCSC|F spin valve

“…To understand feasibility of ferromangetism and superconductivity, and also the role of magnetization in F|S hybrids, many superconducting spintronic SVs had been extensively studied theoretically [76][77][78][79][80][81][82][83][84][85][86] and experimentally [87][88][89][90][91][92][93][94][95][96]. Previous works on F|S heterostructure and superconducting SVs strongly indicates that the superconducting critical temperature is dependent on the orientation of magnetization.…”