A unified approach combining polarized neutron and resonant x-ray magnetic reflectometry has been applied to determine the magnetic structure in an ͓Fe͑35 Å͒ / Gd͑50 Å͔͒ 5 multilayer as a function of temperature and magnetic field. Simultaneous self-consistent refinement of neutron and x-ray data made it possible to resolve the element-specific magnetization profile in the multilayer with unprecedented accuracy. It is shown that the small number of bilayer periods together with the asymmetric termination ͑Fe-top, Gd-bottom͒ lead to unique low-temperature magnetic phases characterized by significant twisting of Fe and Gd magnetic moments and nonuniform distribution of vectorial magnetization within Gd layers. A twisted magnetic state was found to be stable at small magnetic fields and at a low temperature of 20 K, which is well below the compensation temperature of this artificial ferrimagnetic system.

Static and dynamic magnetic properties of a [Fe(35 Å)/Gd(50 Å)] superlattice are investigated experimentally in the temperature range 5-295 K using SQUID magnetometery and the ferromagnetic resonance (FMR) technique at frequencies 7-38 GHz. The obtained magnetization curves and FMR spectra are analysed theoretically using numerical simulation on the basis of the effective field model. At every given temperature, both static and resonance experimental data can be approximated well within the proposed model. However, a considerable temperature dependence of the effective field parameter in gadolinium layers has to be taken into account to achieve reasonable agreement with the experimental data in the entire temperature range studied. To describe the peculiarities of experimental FMR spectra, a non-local diffusion-type absorption term in Landau-Lifshitz equations is considered in addition to the Gilbert damping term. Possible reasons for the observed effects are discussed.

We report on a study of the structural, magnetic and superconducting properties of Nb(25nm)/Gd(d f )/Nb(25nm) hybrid structures of a superconductor/ ferromagnet (S/F) type. The structural characterization of the samples, including careful determination of the layer thickness, was performed using neutron and X-ray scattering with the aid of depth sensitive mass-spectrometry. The magnetization of the samples was determined by SQUID magnetometry and polarized neutron reflectometry and the presence of magnetic ordering for all samples down to the thinnest Gd(0.8nm) layer was shown. The analysis of the neutron spin asymmetry allowed us to prove the absence of magnetically dead layers in junctions with Gd interlayer thickness larger than one monolayer. The measured dependence of the superconducting transition temperature Tc(d f ) has a damped oscillatory behavior with well defined positions of the minimum at d f =3nm and the following maximum at d f =4nm; the behavior, which is in qualitative agreement with the prior work (J.S. Jiang et al, PRB 54, 6119). The analysis of the Tc(d f ) dependence based on Usadel equations showed that the observed minimum at d f =3nm can be described by the so called "0" to "π" phase transition of highly transparent S/F interfaces with the superconducting correlation length ξ f ≈ 4nm in Gd. This penetration length is several times higher than for strong ferromagnets like Fe, Co or Ni, simplifying thus preparation of S/F structures with d f ∼ ξ f which are of topical interest in superconducting spintronics.

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