M. Ślęzak

Magnetism of ultrathin Fe films in MgO/Fe/MgO in epitaxial structures probed by nuclear resonant scattering of synchrotron radiation

Nuclear resonant scattering (NRS) of synchrotron radiation was used to investigate the magnetic anisotropy of iron films in MgO/Fe(t)/MgO(001) structures for t = (4–10) A. The low-temperature NRS spectra were analyzed using a static magnetization model involving two interface-like components and a bulk-like component. We confirmed the existence of perpendicular magnetic anisotropy in MgO/Fe/MgO structures at 10 K with an increasing in-plane component of the magnetization for t > 8 A over the entire thickness of the Fe film. The evolution of the magnetic structure with increasing temperature was studied for an Fe film thickness of 8.8 A, and the temperature dependence of superparamagnetic fluctuations with characteristic frequencies ranging over tens of MHz was interpreted in terms of a spin reorientation transition. We showed that interfacial magnetic moments are less sensitive to thermal excitations than the magnetic moments in the film center, which was attributed to the spin pinning at the interface.

Antiferromagnetic interlayer exchange coupling in epitaxial Fe/MgO/Fe trilayers with MgO barriers as thin as single monolayers

Comparative studies of the magnetic properties of epitaxial Fe/MgO/Fe trilayers, which were directly grown on an MgO(001) crystal and a homoepitaxial MgO buffer layer, were performed to examine the interlayer exchange coupling as a function of the MgO spacer thickness. Measurements of the magneto-optic Kerr effect at room temperature demonstrated that there was a strong antiferromagnetic coupling (AFC) between the Fe layers, which was mediated by the insulating MgO barrier. A measurable AFC was found in a range of MgO thickness (dMgO) from a single monolayer (2 A) to 6 A, which had a maximum strength of −1.15 ergs/cm2 at dMgO = 2.7 A for the Fe/MgO/Fe trilayers that were prepared on the buffered sample and was notably weaker for the trilayers that were prepared directly on the MgO(001).

Magnetization processes in ultrathin Au∕Co∕Au films grown on a bifacial Mo(110)/Mo(540) single crystal

We studied magnetization reversal processes and magnetic anisotropy in ultrathin Au∕Co∕Au films deposited on a bifacial Mo(110)/(540) single crystal. The influence of the Co thickness and miscut angle on the spin reorientation from out-of-plane into in-plane magnetization were investigated by means of the magneto-optical Kerr effect (MOKE). In the case of Co grown on a vicinal Au∕Mo(540) substrate, the perpendicular magnetization component was found throughout the 1–8nm Co thickness range. The canted orientation of magnetization was deduced from vectorial MOKE magnetometry. The out-of-plane switching field, which is 160Oe for the perpendicular magnetization, increases to about 960Oe as observed at 8nm Co thickness on the vicinal part. The experimental data are discussed taking into account both uniaxial out-of-plane and in-plane magnetic anisotropy energy terms. The results indicate the possibility of tuning the perpendicular magnetization component with the use of vicinal substrates, and are important fr...

Magnetic properties of Eu-Fe thin films

We studied the formation of alloys and compounds of the Eu-Fe binary system, in the form of thin films, prepared using molecular beam epitaxy. Diffraction and photoelectron spectroscopy investigations revealed mixing of the elements during the annealing at relatively low temperature. Magnetic studies showed ferromagnetic behavior up to 400 K, and strong thermomagnetic effects and exchange bias indicating the presence of an antiferromagnetic phase and superparamagnetic particles. X-ray photoemission microscopy with dichroic contrast confirmed this hypothesis, showing two types of Eu-Fe alloys with various stoichiometries and showing ferromagnetically ordered particles of 100–500 nm in size. Ferromagnetic particles contain divalent Eu atoms, whereas the antiferromagnetic alloy is probably composed of the trivalent Eu atoms detected in the photoelectron spectra.