The giant spin blocking of tunnel currents discovered by us (Low. Temp. Phys. 36, 186 (2010)) is investigated theoretically and experimentally in ferromagnet F (Co2CrAl)- insulator I- superconductor S (Pb) heterostructures with a wide range of specific resistances (10−7–10−4 Ω · cm2). The magnitude of this effect is found to depend on the specific resistance of the junction in the normal state and on recombination spin depolarization. A theoretical model which provides an adequate description of the tunnelling of spin-polarized electrons in F-I-S junctions is proposed. It is found that the normalized conductivity σFS of an F-I-S tunnel junction can be considerably lower than the fundamental normalized conductivity σNS of an N-I-S junction (where N is a normal metal). The proposed model is used to estimate the degree of spin polarization p of films of the ferromagnetic semimetal Co2CrAl (Heusler alloy) with B2- and L21-type crystal structures, which is close to 1 (p ≈ 0.97). The temperature dependence σFS(T) of a Co2CrAl-I-Pb F-I-S tunnel junction is studied experimentally. A theoretical model is proposed which provides an adequate description of the temperature behavior of the normalized conductivity σFS(T) with features of spin-polarized tunnelling taken into account.

F-I-S tunnel junctions of Co2CrAl-I-Pb and Co2Cr0.6Fe0.4Al-I-Pb based on films of semimetal ferromagnetic Heusler alloys Co2CrAl (Curie temperature TC ≈ 334 K) have been fabricated and the features of spin-polarized current in them studied. A theoretical model of spin blocking of the tunnel current shows that the degree of spin polarization of the conduction electrons in quasi-single crystal films of Co2Cr0.6Fe0.4Al and Co2CrAl with B2- and L21-type order is 0.91–0.97.

A physical model of tunneling processes leading to a nonequilibrium superconducting state in ferromagnet-superconductor junctions is proposed and confirmed experimentally. The model is based on the analysis of experimental current-voltage characteristics and the determination of junction voltage dependences of the energy gap, the effective chemical potential and the effective temperature of quasiparticles in the modified energy distribution of quasiparticles as well as on taking into account the change in the density of electron states due to destruction of the Cooper pairs, caused by the proximity effect.

With allowance for possible deviations of the current–phase relation from the usual sinusoidal dependence, a modified Ferrell–Prange equation is used to examine the steady-state electrodynamics of transparent Josephson junctions in an external magnetic field. It is shown that in this case the penetration of a weak magnetic field into a transparent Josephson junction is generally nonexponential, and the field Hc1 at which vortices arise in transparent junctions and the dependence of the critical current on the magnetic field in them are calculated.

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