Superconducting switching due to a triplet component in the Pb/Cu/Ni/Cu/Co₂Cr_1−xFe_xAl_y spin-valve structure

Abstract

We report the superconducting properties of the Co2Cr1 −x Fe x Al y /Cu/Ni/Cu/Pb spin-valve structure the magnetic part of which comprises the Heusler alloy layer HA = Co2Cr1 −x Fe x Al y with a high degree of spin polarization (DSP) of the conduction band and a Ni layer of variable thickness. The separation between the superconducting transition curves measured for the parallel (α = 0°) and perpendicular (α = 90°) orientation of the magnetization of the HA and the Ni layers reaches up to 0.5 K (α is the angle between the magnetization of two ferromagnetic layers). For all studied samples the dependence of the superconducting transition temperature T c on α demonstrates a deep minimum in the vicinity of the perpendicular configuration of the magnetizations. This suggests that the observed minimum and the corresponding full switching effect of the spin valve is caused by the long-range triplet component of the superconducting condensate in the multilayer. Such a large effect can be attributed to a half-metallic nature of the HA layer, which in the orthogonal configuration efficiently draws off the spin-polarized Cooper pairs from the space between the HA and Ni layers. Our results indicate a significant potential of the concept of a superconducting spin-valve multilayer comprising a half-metallic ferromagnet, recently proposed by A. Singh et al., Phys. Rev. X 2015, 5, 021019, in achieving large values of the switching effect.

Superconducting spin-valve effect in heterostructures with ferromagnetic Heusler alloy layers

“…In general the Pb layer should be sufficiently thin to make the whole SC layer sensitive to the magnetic part of the structure. The optimal thicknesses of the Pb layer for both structure types were determined from the T c (d P b ) curves for the HA RT /Cu/Pb and Ni/Cu/Pb trilayers measured at constant d HA RT = 12 nm and d N i = 5 nm, respectively (for preliminary data see our work [42]).…”

“…(Color online) Record splitting of the SC transition curves for the P and PP configurations of the magnetization of the Ni layer and the applied magnetic field H0 = 3.5 kOe which rotates the magnetization of the HA hot layer for the sample PLAK4216 (Experimental R(T ) dependences are reproduced from Ref. [42]). Shaded rectangle marks the operational area of the SSV.…”

“…Dependence of Tc on the angle α between the direction of the cooling field used to fix the direction of the magnetization of the Ni layer and the applied magnetic field H0 = 1 kOe which rotates the magnetization of the HA RT layer for samples PLAK4212 (a) and for the sample PLAK4216 (b) (experiemntal points in (b) are reproduced from Ref. [42]). Dashed lines depict the estimated angular dependence of the singlet SSV effect.…”

“…Some preliminary data on the use of HA RT and HA hot in different parts of the SSV were reported by us previously in Refs. [41,42].…”

Controllable two- vs three-state magnetization switching in single-layer epitaxial Pd1-xFex films and epitaxial Pd0.92Fe0.08/Ag/Pd0.96Fe0.04 heterostructure

“…The generation of the long-range triplet component of the superconducting pairing at noncollinear orientations of magnetizations in ferromagnetic layered systems is extensively studied in the framework of magnetic Josephson junctions (MJJ) (see reviews [1][2][3] and references therein for early works, and very recent papers [4,5] and references therein), and superconductive spin valves (SSV) [6][7][8][9]. The key points of underlying physics are non-uniform magnetic configurations in the system which mix singlet and triplet superconducting pairing channels.…”