Hard x-ray photoelectron spectroscopy of buried Heusler compounds

This work reports on high energy photoelectron spectroscopy from the valence band of buried Heusler thin films (Co2MnSi and Co2FeAl0.5Si0.5) excited by photons of about 6?keV energy. The measurements were performed on thin films covered by MgO and SiOx with different thicknesses from 1 to 20?nm of the insulating layer and additional AlOx or Ru protective layers. It is shown that the insulating layer does not affect the high energy spectra of the Heusler compound close to the Fermi energy. The high resolution measurements of the valence band close to the Fermi energy indicate a very large electron mean free path of the electrons through the insulating layer. The spectra of the buried thin films agree well with previous measurements from bulk samples. The valence band spectra of the two different Heusler compounds exhibit clear differences in the low lying s bands as well as close to the Fermi energy.

[1]  T. Ishikawa,et al.  High resolution-high energy x-ray photoelectron spectroscopy using third-generation synchrotron radiation source, and its application to Si-high k insulator systems , 2003 .

[2]  Takayuki Ishikawa,et al.  Spin-dependent tunneling characteristics of fully epitaxial magnetic tunneling junctions with a full-Heusler alloy Co2MnSi thin film and a MgO tunnel barrier , 2006 .

[3]  E. Rotenberg,et al.  Direct extraction of exchange splittings from magnetic X-ray dichroism in photoelectron spectroscopy , 1998 .

[4]  Jürgen Kübler,et al.  Formation and coupling of magnetic moments in Heusler alloys , 1983 .

[5]  Marek Przybylski,et al.  Magnetic properties and spin polarization of Co 2 MnSi Heusler alloy thin films epitaxially grown on GaAs(001) , 2005 .

[6]  T. Marukame,et al.  Epitaxial Growth of Full-Heusler Alloy Co$_2$MnSi Thin Films on MgO-Buffered MgO Substrates , 2006, IEEE Transactions on Magnetics.

[7]  High energy, high resolution photoelectron spectroscopy of Co2Mn1−xFexSi , 2006, cond-mat/0611120.

[8]  G. Fecher,et al.  Detection of the valence band in buried Co2MnSi–MgO tunnel junctions by means of photoemission spectroscopy , 2008 .

[9]  H. Sukegawa,et al.  Preparation and characterization of highly L21-ordered full-Heusler alloy Co2FeAl0.5Si0.5 thin films for spintronics device applications , 2008 .

[10]  A. Sekiyama,et al.  High-energy bulk-sensitive angle-resolved photoemission study of strongly correlated systems , 2004 .

[11]  G. Fecher,et al.  Spintronics: a challenge for materials science and solid-state chemistry. , 2007, Angewandte Chemie.

[12]  S. Doniach,et al.  X-ray photoemission spectroscopy , 1974, Nature.

[13]  T. Marukame,et al.  High tunnel magnetoresistance in fully epitaxial magnetic tunnel junctions with a full-Heusler alloy Co2Cr0.6Fe0.4Al thin film , 2006 .

[14]  Koichiro Inomata,et al.  Highly spin-polarized materials and devices for spintronics∗ , 2008, Science and technology of advanced materials.

[15]  D. A. Shirley,et al.  Multiplet splitting of core-electron binding energies in transition-metal ions , 1969 .

[16]  Keisuke L. I. Kobayashi.  High-resolution hard X-ray photoelectron spectroscopy: Application of valence band and core-level spectroscopy to materials science , 2005 .

[17]  K.H.J. Buschow,et al.  New Class of Materials: Half-Metallic Ferromagnets , 1983 .

[18]  Thole,et al.  Spin polarization and magnetic dichroism in photoemission from core and valence states in localized magnetic systems. III. Angular distributions. , 1994, Physical review. B, Condensed matter.

[19]  G. Materlik,et al.  X‐ray standing waves and x‐ray photoemission measurements in the energy range 2.7–7 keV , 1992 .

[20]  R. Tommasini,et al.  Experimental setup for high energy photoemission using synchrotron radiation , 2005 .

[21]  W. Kuch,et al.  Spin polarization of single-crystalline Co2MnSi films grown by PLD on GaAs(0 0 1) , 2005 .

[22]  N. Tezuka,et al.  175% tunnel magnetoresistance at room temperature and high thermal stability using Co2FeAl0.5Si0.5 full-Heusler alloy electrodes , 2006 .

[23]  T. Koide,et al.  X-ray absorption spectroscopy and x-ray magnetic circular dichroism of epitaxially grown Heusler alloy Co2MnSi ultrathin films facing a MgO barrier , 2007 .

[24]  T. Ishikawa,et al.  Development of hard X-ray photoelectron spectroscopy at BL29XU in SPring-8 , 2005 .

[25]  Claudia Felser,et al.  Calculated electronic and magnetic properties of the half-metallic, transition metal based Heusler compounds , 2006, cond-mat/0611179.

[26]  G. Fecher,et al.  Rational design of new materials for spintronics: Co2FeZ (Z=Al, Ga, Si, Ge) , 2008, Science and technology of advanced materials.

[27]  N. Tezuka,et al.  Tunnel magnetoresistance for junctions with epitaxial full-Heusler Co2FeAl0.5Si0.5 electrodes with B2 and L21 structures , 2006 .

[28]  K. Siegbahn.  Preface to hard X-ray photo electron spectroscopy (HAXPES) , 2005 .

[29]  G. Fecher,et al.  Substituting the main group element in cobalt–iron based Heusler alloys: Co2FeAl1−xSix , 2006, cond-mat/0612241.

[30]  T. Marukame,et al.  Fabrication of fully epitaxial magnetic tunnel junctions with a Co2MnSi thin film and a MgO tunnel barrier , 2007 .

[31]  Takayuki Ishikawa,et al.  Highly spin-polarized tunneling in fully epitaxial Co2Cr0.6Fe0.4Al∕MgO∕Co50Fe50 magnetic tunnel junctions with exchange biasing , 2007 .

[32]  G. Fecher,et al.  Structural and magnetic properties of Co2FeAl1−xSix , 2007 .

[33]  N. Tezuka,et al.  Giant Tunnel Magnetoresistance at Room Temperature for Junctions using Full-Heusler Co2FeAl0.5Si0.5 Electrodes , 2007 .

[34]  Kazuhiro Hono,et al.  Ab initio predictions for the effect of disorder and quarternary alloying on the half-metallic properties of selected Co2Fe-based Heusler alloys , 2007 .

[35]  J. Zegenhagen,et al.  Hard X-ray photoelectron spectroscopy from 5 14.5 keV , 2004 .

[36]  S. Yuasa,et al.  Giant tunneling magnetoresistance in MgO-based magnetic tunnel junctions and its industrial applications , 2006, 2006 IEEE Nanotechnology Materials and Devices Conference.

[37]  G. Fecher,et al.  Correlation in the transition metal based Heusler compounds Co2MnSi and Co2FeSi , 2006, cond-mat/0601671.

[38]  W. Meisel.  Corrosion processes and their inhibition as studied by Mössbauer conversion and other electron spectroscopies , 1989 .

[39]  C. Nordling,et al.  Precision Method for Obtaining Absolute Values of Atomic Binding Energies , 1957 .

[40]  M. Martins,et al.  Multiplet splitting and valence-shell recoupling in the core-level 2 p photoelectron spectrum of atomic Mn and of Mn compounds , 2001 .

[41]  E. Kurmaev,et al.  Local moments in Mn-based Heusler alloys and their electronic structures , 1999 .

[42]  H. Sukegawa,et al.  Fabrication of fully epitaxial magnetic tunnel junctions using L21-ordered Co2FeAl0.5Si0.5 electrodes and their tunneling magnetoresistance characteristics , 2008 .

[43]  R. Tommasini,et al.  High-energy photoemission in silver: resolving d and sp contributions in valence band spectra , 2005 .

[44]  G. Fecher,et al.  Properties of the quaternary half-metal-type Heusler alloy Co2Mn1-xFexSi , 2006, cond-mat/0606108.

[45]  D. R. Penn,et al.  Calculations of electron inelastic mean free paths. III. Data for 15 inorganic compounds over the 50–2000 eV range , 1991 .

[46]  Takayuki Ishikawa,et al.  Fabrication of fully epitaxial Co2MnSi∕MgO∕Co2MnSi magnetic tunnel junctions , 2008 .