Márcio M. Soares

Robust perpendicular exchange coupling in an ultrathin CoO/PtFe double layer: Strain and spin orientation

We report on the exchange coupling and magnetic properties of a strained ultrathin CoO/PtFe double-layer with perpendicular magnetic anisotropy. The cobalt oxide growth by reactive molecular beam epitaxy on a Pt-terminated PtFe/Pt(001) surface gives rise to an hexagonal surface and a monoclinic distorted CoO 3nm film at room temperature. This distorted ultrathin CoO layer couples with the PtFe(001) layer establishing a robust perpendicular exchange bias shift. Soft x-ray absorption spectroscopy provides a full description of the spin orientations in the CoO/PtFe doublelayer. The exchange bias shift is preserved up to the Neel antiferromagnetic ordering temperature of TN=293 K. This unique example of selfsame value for blocking and ordering temperatures, yet identical to the bulk ordering temperature, is likely related to the original strain induced distortion and strengthened interaction between the two well-ordered spin layers.

Emergence of ferromagnetism and Jahn-Teller distortion in LaMn1−xCrxO3 (x < 0.15)

The emergence of a ferromagnetic component in LaMnO3 with low Cr-for-Mn substitution has been studied by x-ray absorption spectroscopy and x-ray magnetic circular dichroism at the Mn and Cr K edges. The local magnetic moment strength for the Mn and Cr are proportional to each other and follows the macroscopic magnetization. The net ferromagnetic components of Cr3+ and Mn3+ are found antiferromagnetically coupled. Unlike hole doping by La site substitution, the inclusion of Cr3+ ions up to x = 0.15 does not decrease the Jahn-Teller (JT) distortion and consequently does not signi cantly a ect the orbital ordering. This demonstrates that the emergence of the ferromagnetism is not related to JT weakening and likely arises from a complex orbital mixing.

Magnetic and structural properties of the Fe layers in CoO/Fe/Ag(001) heterostructure

The influence of interfacial oxidation on the magnetic behaviour of CoO covered Fe/Ag(001) is reported. Coverage with CoO causes the formation of a mixed Fe2O3-Fe3O4 interfacial oxide layer. The depth of the Fe-oxide varies with the thickness of pre-covered Fe and above 8 monolayers (MLs) of Fe the oxide depth becomes constant at 2 ML. Differences in exchange bias and coercivity obtained from magnetic field and zero field cooling nearly vanish above 8 ML Fe thickness, showing a direct correlation between the magnetic behaviour of Fe and structure of the interfacial Fe-oxide layer.

The Coherent X-ray Sub-micro and Nanoprobe Stations for the CARNAUBA Beamline at the Sirius-LNLS Storage Ring.

CARNAÚBA (Coherent X-Ray Nanoprobe Beamline) is the tender-to-hard X-ray nanoprobe under construction at the new Brazilian synchrotron light source SIRIUS [1]. The beamline provides two separated experimental stations, one with sub-micrometer resolution and another with nanometer resolution, to cover various analysis techniques, including XRD, XAS, XRF, XEOL, CDI and ptychography with 2D and 3D imaging capabilities exploring the coherent properties of the light. The innovative modified-Delta undulator, with four independent jaws, able to deliver any polarization, is optimized to provide photons with vertical polarization allowing for scattering in the horizontal plane from the source up to the endstations, with unitary polarization factor. The all achromatic CARNAÚBA optics, based on state-of-theart KB mirrors, covers continuously the energy range from 2.05 to 15 keV with a resolution of E/E=10 , using an in-house developed four-bounce crystal monochromator. An unprecedent coherent flux @Si(111)BW close to 10 – 10 ph/s/100mA will be delivered [2].

Strain driven monoclinic distortion of ultrathin CoO films in the exchange-coupled CoO/FePt/Pt(0 0 1) system

The structure and strain of ultrathin CoO films grown on a Pt(0 0 1) substrate and on a ferromagnetic FePt pseudomorphic layer on Pt(0 0 1) have been determined with in situ and real time surface x-ray diffraction. The films grow epitaxially on both surfaces with an in-plane hexagonal pattern that yields a pseudo-cubic CoO(1 1 1) surface. A refined x-ray diffraction analysis reveals a slight monoclinic distortion at RT induced by the anisotropic stress at the interface. The tetragonal contribution to the distortion results in a ratio [Formula: see text], opposite to that found in the low temperature bulk CoO phase. This distortion leads to a stable Co(2+) spin configuration within the plane of the film.