Conductance features in point contact Andreev reflection spectra.

Point contact Andreev reflection (PCAR) spectroscopy is a common technique for determining the spin polarization of a ferromagnetic sample. The polarization is extracted by measuring the bias dependence of the conductance of a metallic/superconducting point contact. Under ideal conditions, the conductance is dominated by Andreev reflection and the Blonder-Tinkham-Klapwijk (BTK) model can be used to extract a value for the polarization. However, PCAR spectra often exhibit unwanted features in the conductance that cannot be appropriately modelled with the BTK theory. In this paper we isolate some of these unwanted features and show that any further extraction of the spin polarization from these non-ideal spectra proves unreliable. Understanding the origin of these features provides an objective criterion for rejection of PCAR spectra unsuitable for fitting with the modified BTK model.

Experimental observation of the spin screening effect in superconductor/ferromagnet thin film heterostructures.

We have studied the nuclear magnetic resonance (NMR) of 51V nuclei in the superconductor/ferromagnet thin film heterostructures Pd_{1-x}Fe_{x}/V/Pd_{1-x}Fe_{x} and Ni/V/Ni in the normal and superconducting state. Whereas the position and shape of the NMR line in the normal state for the trilayers is identical to that observed in a single V layer, in the superconducting state the line shape definitely changes, developing a systematic distortion of the high-field wing of the resonance line. We consider this as the first experimental evidence for the penetration of ferromagnetism into the superconducting layer, a phenomenon which has been theoretically predicted recently and dubbed the spin screening effect.

Superconducting spin valve effect of a v layer coupled to an antiferromagnetic [Fe/V] superlattice.

We studied superconducting V layers deposited on an antiferromagnetically coupled [Fe(2)V(11)](20) superlattice. The parallel upper critical magnetic field exhibits an anomalous T dependence up to the ferromagnetic saturation field of the superlattice, indicating that the superconducting transition temperature T(S) decreases when rotating the relative sublattice magnetization directions of the superlattice from antiparallel to parallel. This proves that the pair breaking effect of a Fe2 layer is reduced if at a distance of 1.5 nm a second Fe2 layer with antiparallel spin orientation exists.

Magnetic superlattices with variable interlayer exchange coupling: a new approach for the investigation of low-dimensional magnetism.

We have investigated the magnetic order in an [Fe(2)/(VHx)(13)] x 200 superlattice as a function of temperature and hydrogen content in the vanadium layers. A J(radially)-T magnetic phase diagram was established where J(radially) denotes the interlayer exchange coupling between adjacent Fe planes. We propose that Fe/V superlattices, in which the ratio of interlayer to intralayer coupling can be tuned continuously and reversibly via hydrogen in the nonmagnetic vanadium, offer a new approach for the study of low-dimensional magnetism and crossover effects near the transition from ferromagnetic to antiferromagnetic order.