Current-field diagram of magnetic states of a surface spin valve in a point contact with a single ferromagnetic film

We present a study of the influence of an external magnetic field H and an electric current I on the spin-valve (SV) effect in point contact between a ferromagnetic thin film (F) and a sharp tip of a nonmagnetic metal (N). To explain our observations, we propose a model of a local surface SV which is formed in such a N/F contact. In this model, a ferromagnetic cluster at the N/F interface plays the role of the free layer in this SV. This cluster exhibits a larger coercive field than the bulk of the ferromagnetic film, presumably due to its nanoscale nature. Finally, we construct a magnetic state diagram of the surface SV as a function of I and H

Stimulated emission and absorption of photons in magnetic point contacts

Point contacts between high anisotropy ferromagnetic SmCo5 and normal metal Cu are used to achieve a strong spin-population inversion in the contact core. Subjected to microwave irradiation in resonance with the Zeeman splitting in Cu, the inverted spin population relaxes through stimulated spin-flip photon emission, detected as peaks in the point-contact resistance. Resonant spin-flip photon absorption is detected as resistance minima, corresponding to sourcing the photon field energy into the electrical circuit. These results demonstrate fundamental mechanisms that are potentially useful in designing metallic spin-based lasers

Josephson effect and Andreev reflection in Ba₁₋xNaxFe₂As₂ (x = 0.25 and 0.35) point contacts

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

Point-contact-spectroscopy investigation of the Kondo size effect in CuCr and AuFe alloys

Size effects in Kondo scattering are studied on CuCr and AuFe alloys (TK=2 K and 0.2 K, respectively) by applying point-contact spectroscopy in break-junction type contacts. It is shown that as the contact diameter is decreased under the condition of ballistic electron transport, the size effect enhances the interaction of the conduction electrons with the Kondo impurity (as compared to the phonons) and increases the Kondo temperature in the contact region. In an external magnetic field the size effect decreases the negative magnetoresistance in CuCr and suppresses the Kondo peak splitting in AuFe

Size-effect of Kondo scattering in point contacts (revisited)

The size-effect of Kondo-scattering in nanometer-sized metallic point contacts is measured with the simplified, mechanically-controlled break-junction technique for CuMn alloy of different Mn concentrations: 0.017; 0.035; and 0.18 (± 0.017) at.%. The results are compared with our previous publication on nominally 0.1 at.% CuMn alloy [1,2]. The increase of width of the Kondo resonance and enhanced ratio of Kondo-peak intensity to electron-phonon scattering intensity is observed for contacts with sizes smaller than 10 nm. From the comparison of electron-phonon scattering intensity for the pressure-type contacts, which correspond to the clean orifice model, we conclude that the size effect is observed in clean contacts with the shape of a channel (nanowire)

Spin-valve effects in point contacts to exchange biased Сo₄₀Fe₄₀B₂₀ films

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

Point-contact-spectroscopy evidence of quasi-particle interactions in RNi₂B₂C(R=Ho, Y)

The point-contact (PC) d²V/dI²-spectra of HoNi₂B₂C and YNi₂B₂C reveal structure at applied voltages corresponding to the phonon frequencies. At about 4 meV a maximum is observed in the phonon density of states by analogy to the soft-phonon structure in neutron scattering experiments for LuNi₂B₂C [ P. Dervenagas et al., Phys. Rev. B52, R9839 (1995)] and YNi₂B₂C [H. Kawano et al., Cech. J. Phys. 46, S2-825 (1996) Phys. Rev Lett. 77, 4628 (1996)]. In the Ho compound the low-energy phonon peak is suppressed by an applied magnetic field in an anisotropic way, pointing to an interaction between the phonons and the magnetic systems Surprisingly, in the nonmagnetic Y compound the 4-meV peak is also suppressed by a magnetic field. In the Ho-compound contacts which show the «quasi-thermal» behavior, the detailed magnetic-field and temperature dependences of the PC spectra suggest that the magnetic order is destroyed due to the coupled phonon-magnon subsystem which is driven out of equilibrium by electrons that pass through the contact, by analogy with the nonequilibrium phonon-induced destruction of the superconducting state in point contacts [I. K. Yanson et al., JETP Lett 45, 543 (1987)]. The PC electron-phonon interaction (EPI) spectral functions are reconstructed and the estimates for the λ-parameter yield values of the order of 0.1. Comparison with PC EPI spectra of nonsuperconducting and nonmagnetic LaNi₂B₂C [I K. Yanson et al, Phys Rev. Lett. 78, 935 (1997)], as well as the comparative study of PC EPI and Andreev-retlection spectra tor various contacts with superconducting Ho and Y compounds suggest that the low-energy part ot the electron-quasi-particle interaction spectral function is responsible for the Cooper pairing in these materials