N. Stojic

Publications (7)0 Total impact

• Source

  Available from: ArXiv

  Article: Temperature dependence of surface stress across an order-disorder transition: p(1x2)O/W(110)

  N. Stojic, T O Mentes, N. Binggeli, M. A. Nino, A. Locatelli, E. Bauer
  [show abstract] [hide abstract]
  ABSTRACT: Strain relaxations of a p(1x2) ordered oxygen layer on W(110) are measured as a function of temperature across the disordering transition using low-energy electron diffraction. The measured strains approach values of 0.027 in the [1-10] and -0.053 in the [001] direction. On the basis of the measured strain relaxations, we give quantitative information on temperature-dependent surface stress using the results of ab initio calculations. From the surface formation energy for different strains, determined by first-principles calculations, we estimate that surface stress changes from -1.1 for the ordered phase to -0.2N/m for the disordered one along [1-10], and from 5.1 to 3.4 N/m along [001]. Moreover, our observation that the strains scale inversely with domain size confirms that the strain relaxation takes place at the domain boundaries. Comment: 8 pages, 5 figures
  03/2010;
• Source

  Available from: Maya Kiskinova

  Article: Strain relaxation in small adsorbate islands: O on W(110)

  T O Mentes, N. Stojic, N. Binggeli, M. A. Nino, A. Locatelli, L Aballe, M Kiskinova, E. Bauer
  [show abstract] [hide abstract]
  ABSTRACT: The stress-induced lattice changes in a p(1x2) ordered oxygen layer on W(110) are measured by low-energy electron diffraction. We have observed that small oxygen islands show a mismatch with the underlying lattice. Our results indicate that along [1-10] the average mismatch scales inversely with the island size as 1/L for all oxygen coverages up to 0.5 ML, while along [001] it is significant only for the smallest oxygen islands and scales as a higher power of the inverse island size. The behaviour along [1-10] is described by a one-dimensional finite-size Frenkel-Kontorova model. Using this model, together with calculated force constants, we make a quantitative estimate for the change of surface-stress upon oxygen adsorption. The result is consistent with our ab-initio calculations, which give a relative compressive stress of -4.72 N/m along [1-10] and a minute relative tensile stress of 0.15 N/m along [001]. The scaling along [001] is qualitatively explained as an effect induced by the lattice relaxation in the [1-10] direction. Comment: 22 pages, 5 figures
  04/2008;
• Source

  Available from: arxiv.org

  Article: Role of magnetic and orbital ordering at the metal-insulator transition in NdNiO3

  V. Scagnoli, U Staub, A. M. Mulders, M. Janousch, G. I. Meijer, G. Hammerl, J. M. Tonnerre, N. Stojic
  [show abstract] [hide abstract]
  ABSTRACT: Soft x-ray resonant scattering at the Ni L2,3 edges is used to test models of magnetic and orbital-ordering below the metal-insulator transition in NdNiO3. The large branching ratio of the L3 to L2 intensities of the (1/2,0,1/2) reflection and the observed azimuthal angle and polarization dependence originates from a non collinear magnetic structure. The absence of an orbital signal and the non collinear magnetic structure show that the nickelates are materials for which orbital ordering is absent at the metal-insulator transition. Comment: 10 pages, 4 figures, Physical Review B rapid communication, to be published
  03/2006;
• Source

  Available from: arxiv.org

  Article: Surface magnetism of Rh(001) from LDA+U calculations

  N. Stojic, N. Binggeli, M. Altarelli
  [show abstract] [hide abstract]
  ABSTRACT: We report calculations indicating the presence of a surface magnetic moment for Rh(001), motivated by the detection of a finite moment by magnetic linear dichroism experiments. We show that, while the density functional with the local density or generalized gradient approximations (LDA and GGA) for exchange and correlation yields a non-magnetic ground state, the application of the GGA plus on-site Coulomb interaction U method predicts surface magnetism, thus offering a solution to the long-standing discrepancy between experiment and theory. The calculated moment on the outermost Rh atom increases with the strength of the effective on-site parameter Ueff=U-J, for Ueff>=1.2 eV, and is as large as 1.24 mu_B for Ueff=2.5 eV. Comment: 4 pages, 2 figures Accepted as Rap. Comm. Phys. Rev. B
  03/2006;
• Source

  Available from: Stefan Stanescu

  Article: Evidence of Orbital Ordering in Jahn-Teller Undistorted LaSr$_{2}$Mn$_{2}$O$_{7}$

  S. B. Wilkins, N. Stojic, T. A. W. Beale, N. Binggeli, P. Bencok, S. Stanescu, J. F. Mitchell, P. Abbamonte, P. D. Hatton, M. Altarelli
  [show abstract] [hide abstract]
  ABSTRACT: Resonant soft x-ray diffraction has been used to probe the temperature dependent orbital and magnetic structure of $\mathrm{LaSr_{2}Mn_{2}O_7}$. Previous crystallographic studies have shown that this material has almost no MnO$_{6}$ oxygen displacement due to Jahn-Teller distortions at low temperatures. Within the low-temperature A-type antiferromagnetic phase, we found strong intensity at the $({1/4},{1/4},0)$ orbital and $LaSr_{2}Mn_{2}O_7$ magnetic reflections. This shows that even in the near absence of Jahn-Teller distortion, this compound is strongly orbitally ordered. A fit to the Mn $L$-edge resonance spectra demonstrates the presence of orbital ordering of the Mn$^{3+}$ ions with virtually no Jahn-Teller crystal field in addition to possible Mn$^{3+}$ and Mn$^{2+}$~like valence fluctuations.
  01/2005;
• Source

  Available from: Christopher Castleton

  Article: Resonant Soft X-ray Scattering Investigation of Orbital and Magnetic Ordering in $\rm La_{0.5}Sr_{1.5}MnO_4$

  S. B. Wilkins, N. Stojic, T. W. A. Beale, N. Binggeli, C. W. M. Castleton, P. Bencok, D. Prabhakaran, A. T. Boothroyd, P. Hatton, M. Altarelli
  [show abstract] [hide abstract]
  ABSTRACT: We report resonant x-ray scattering data of the orbital and magnetic ordering at low temperatures at the Mn $L_{\rm 2,3}$ edges in \lsmo. The orderings display complex energy features close to the Mn absorption edges. Systematic modeling with atomic multiplet crystal field calculations was used to extract meaningful information regarding the interplay of spin, orbital and Jahn-Teller order. These calculations provide a good general agreement with the observed energy dependence of the scattered intensity {for a} dominant orbital ordering of the $ d_{x^2 - z^2} / d_{y^2 - z^2} $ type. In addition, the origins of various spectral features are identified. The temperature dependence of the orbital and magnetic ordering was measured and displays a strong interplay between the magnetic and orbital order parameters. Comment: 6 Figures, Submitted to Physical Review B
  10/2004;
• Article: Surfavce Magnetism of Rh(001) from LDA+U calculations

  N. Stojic, N. Binggeli, M. Altarelli
  [show abstract] [hide abstract]
  ABSTRACT: Journal article
  Phys. Rev. B 73(2006),100405(R).