Electronic phenomena studied in the nordic countries

Spin sensitive spectroscopy studies at MAX IV-lab: the magnetism and electronic structure of new spintronic materials

Not scheduled

15m

Max IV Lund

Speaker

Dr Dimitri Arvanitis (Physics and Astronomy, Uppsala University)

Description

We present some of the opportunities specifically offered by synchrotron radiation based spectroscopy in the soft x-ray and the VUV spectral domains to characterize the magnetism and electronic structure of materials suitable for spintronic applications. Spintronic materials exploit the intrinsic spin of the electron in addition to the electron charge. We present studies performed at MAX IV-lab, at the I1011 and I3 beamlines, which allow probing both the spin and electronic state of the photo-excited atoms, by control of the polarization state of the x-rays as well as the characterization of the spin state of the photoemitted electrons. We discuss results from the dilute magnetic semiconductors (DMS) systems GaN doped with Fe and ZnO doped with Bi, using soft x-ray X-ray Absorption Spectroscopy (XAS). [1,2] We also discuss XAS and spin resolved photoemission results of molecular adsorption on ferromagnetic surfaces. [3] We use the chiral 1,2-diphenyl-1,2-ethanediol (DPED) molecule, which is adsorbed in an enantio-pure form on a ferromagnetic and a non-ferromagnetic surface. For the DMS systems, XAS at the oxygen and nitrogen K-edges allow to characterize the contribution of the oxygen and nitrogen 2p electronic states in the magnetism of Fe doped GaN and Bi doped ZnO. [1,2] Using the I1011 beamline at the MAX II storage ring, it has been possible to obtain weak x-ray magnetic circular dichroism (XMCD) signals in the range of 3 10$^{-3}$ of the atomic cross section at these edges. The GaN system doped with Fe, allows to illustrate the importance of a good control of the polarization state of the x-rays. For this system by recording the XMCD at the Fe L-edges we measure the spin and orbital moments of the ferromagnetic component of the magnetisation. At the I1011 beamline, it has also been possible to systematically record the small X-ray Linear Magnetic Dichroism (XLMD) signal at the Fe L-edges of Fe thin films and of diluted Fe in GaN. [4] XLMD allows to measure the magnetic moment of the Fe atoms also in the anti-ferromagnetic state. We finally discuss the observation of X-ray Natural Circular Dichroism (XNCD) in the case of enantio-pure DPED molecules adsorbed on a non-ferromagnetic surface. Chiral molecules on surfaces can produce spin polarisation along different directions acting not only as spin filters but also as spin polarisers. [3] We acknowledge the Polish NCN Grant No. 2011/03/D/ST3/02654 and the Carl Tryggers foundation for scientific research, contracts CTS 14-32 and CTS 16-32. 1. I. A. Kowalik, A. Persson, M. Á. Niño et al. Phys. Rev. B 85, 184411 (2012) 2. Juwon Lee, N. G. Subramaniam, I. A. Kowalik et al. Sci. Rep. 5, 17053 (2015) 3. M. Á. Niño, I. A. Kowalik, F. J. Luque et al. Adv. Mater. 26, 7474 (2014) 4. I. A. Kowalik, Acta Physica Polonica A, 127, 831 (2015)