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The magnetic profile of the Si(100)/NiO(35 nm)/NiFe(10 nm)/Ta(1 nm) sample has been obtained by X-ray absorption spectroscopy (XAS) and the X-ray magnetic circular dichroism (XMCD). Two experimental procedures were used. In the procedure 1, the magnetic depth profile has been determines using samples deposited with different NiFe thicknesses, Si(100)/NiO(35 nm)/NiFe(t)/Ta(1 nm), t = 1 , 3 , 5 , 7 , 10 nm . In procedure 2, the sample (NiFe=10 nm), was thinned by several in situ sputtering cycles with Ar+ ions, followed by XAS and XMCD analysis. In both procedures, the calculated magnetic moments values tend to decrease close to interface with the NiO antiferromagnetic (AF) layer, however, this decreasement is more evidenced in the sputtered sample. There is no charge transfer between Ni and Fe in the inner part of the NiFe layer, a reduction of the m orb / m spin eff has been found at the NiFe/NiO interface. Procedure 1 emerged as the most indicated to analyse the interface region.

Two superconducting intermetallic compounds in the Ni-Bi system, namely NiBi and NiBi3, can be formed as result of interdiffusion, if Ni/Bi are produced as bilayers at room temperature by pulsed laser deposition (PLD). These two equilibrium phases are responsible for the observed superconductivity in this kind of bilayer material. Due to different behavior in external magnetic fields, there appear two-step superconducting transitions in the electrical transport measurements. In this work we studied the superconducting and magnetic properties of the Ni-Bi bilayers with the formation of the two intermetallic compounds, NiBi and NiBi3, which have similar Tc ~ 4.0 K but very different upper critical magnetic fields at zero temperature [Bc2(0)]. The magnetic hysteresis loops of the pure NiBi3 phase show the behavior of a weak type II superconductor without strong pinning effect. Upon formation of the NiBi phase caused by highly energetic atoms during pulsed laser deposition, strong pinning effects appeared in the hysteresis loops below Tc. The isotherm V(I) curves show that the residual Ni layer does not induce spontaneous vortices in the NiBi or NiBi3 phases.

57Fe Mossbauer effect (ME) experiments have been performed on RNiBC (R=Er, Ho, Dy, Tb, Gd) compounds. Below the magnetic ordering temperatures, TM, the 57Fe ME spectra show a transferred magnetic hyperfine field at the Fe (Ni) site for Tb and Er, but such a field is absent for Ho, Dy and Gd. The TM for RNiBC do not scale linearly with the de Gennes factor, and the crystal field effects in the different types of magnetic order of these compounds may be responsible for this behavior.

Features of the magnetic and charge ordering of the Fe3O2BO3 ludwigite have been studied using Mossbauer spectroscopy in the range of 4 K T K . From the temperature dependence of the magnetic hyperfine fields (Bhf), associated to four different iron sites, three magnetic transitions, at 112, 73 and 40 K, can be distinguished in agreement with previous magnetization measurements. In the temperature region where a weak ferromagnetism appears, the Bhf of some Fe sites show two different values related with different canting angles.