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Nonlinear current-voltage characteristics and magnetoresistance of point contacts between a normal metal (N) and films of amorphous ferromagnet (F) Сo₄₀Fe₄₀B₂₀ of different thickness, exchange-biased by antiferromagnetic Mn8₀Ir₂₀ are studied. A surface spin valve effect in the conductance of such F–N contacts is observed. The effect of exchange bias is found to be inversely proportional to the Сo₄₀Fe₄₀B₂₀ film thickness. This behavior as well as other magneto-transport effects we observe on single exchange-pinned ferromagnetic films are similar in nature to those found in conventional three-layer spin-valves.

I(V) characteristics and their first derivatives of ScS and ScN-type (S is superconductor, c is constriction, N is normal metal) point contacts (PCs) based on Ba₁₋xNaxFe₂As₂ (x = 0.25 and 0.35) were studied. ScS-type PCs with S = Nb,Ta, and Pb show Josephson-like resistively shunted I(V) curves with microwave induced Shapiro steps which satisfy relation 2eV = ω. The IcRN product (Ic is critical current, RN is normal state PC resistance) in these PCs is found to be up to 1.2 mV. All this data with the observed dependence of the Ic on the microwave power of ScS PCs with Pb counterelectrode indicates the presence of the singlet s-wave type pairing in Ba₁₋xNaxFe₂As₂. From the dV/dI(V) curves of ScN-type PCs demonstrating Andreev-reflection like features, the superconducting gap ∆ ratio 2∆/kBTc = 3.6 ± 1 for the compound with x = 0.35 was evaluated. Analysis of these dV/dI(V) at high biases V, that is well above ∆, testifies transition to the thermal regime in PCs with a voltage increase.

The point-contact spectra of the Andreev reflection dV / dI curves of the superconducting rare-earth nickel borocarbide ErNi₂B₂C (Tc≈11K) have been analyzed in the «one-gap» and «two-gap» approximations using the generalized Blonder–Tinkham–Klapwijk model and the Beloborod'ko model allowing for the pair-breaking effect of magnetic impurities. Experimental and calculated curves have been compared not only in shape, but in magnitude as well, which provide more reliable data for determining the temperature dependence of the energy gap (or superconducting order parameter) Δ(T). The anisotropic effect of antiferromagnetic ordering at TN≈6K on the superconducting gap/order parameter has been determined: as the temperature is lowered, Δ decreases by∼25% in the c-direction and only by∼4% in the ab-plane. It is found that the pair-breaking parameter increases in the vicinity of the magnetic transitions, the increase being more pronounced in the c-direction. The efficiency of the models was tested for providing Δ(T) data for ErNi₂B₂C from Andreev reflection spectra.

Analysis of the point-contact spectroscopy (PCS) data on the new dramatic high-Tc superconductor magnesium diboride MgB₂ reveals quite different behavior of two disconnected σ and π electronic bands, deriving from their anisotropy, different dimensionality, and electron—phonon interaction. PCS allows direct registration of both the superconducting gaps and electron—phonon interaction spectral function of the two-dimensional σ and three-dimensional π band, establishing correlation between the gap value and intensity of the high-Tc driving force — the E₂g boron vibration mode. PCS data on some nonsuperconducting transition-metal diborides are surveyed for comparison.

The superconducting gap in a CeRu₂ single crystal is investigated by point contacts. BCS-like behavior of the gap Δ in the temperature range below Tc* (Tc*

The measured dV/dI(V) curves of point contacts between the intermetallic compound CeRu2 in the superconducting state and the normal metal Cu correspond fairly well to the Blonder-Tinkham -Klapwijk model. It is used to obtain temperature and magnetic field dependence of the superconducting gap D. The D(T) dependence corresponds well to the BCS theory with 2D(0)/kbTc*=3.1±0.1. Additionally, a region of gapless superconductivity between Tc*»4,4-5,4K and Tcbulk»6.2K is found. The gap decreases approximately linearly in a magnetic field and vanishes in a field Bc*»3.5T, which is well below the upper critical field Bc2»6T and close to the irreversibility field.

We have measured the dV/dI vs. V characteristics of point contacts between the heavy-fermion superconductor URu₂Si₂ and the conventional superconductors Zn and NbTi. Contacts between URu₂Si₂ and Zn behave like a superconductor—normal metal—superconductor junction with a thick normal layer in the heavy-fermion part of the contact and show Andreev-reflection type structures related to both the heavy-fermion and the conventional superconductors. In contrast, contacts between URu₂Si₂ and NbTi become superconducting at low bias currents. The data indicate that proximity induced superconductivity is important for the coupling of the two types of superconductivity. With such contacts we also fabricated a closed-loop setup with two NbTi contacts on a URu₂Si₂ sample, which showed SQUID oscillation in a small magnetic field.