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4f occupancy and magnetism of rare-earth atoms adsorbed on metal substrates
Singha, Aparajita,Baltic, Romana,Donati, Fabio,Wä,ckerlin, Christian,Dreiser, Jan,Persichetti, Luca,Stepanow, Sebastian,Gambardella, Pietro,Rusponi, Stefano,Brune, Harald American Physical Society 2017 Physical Review B Vol.96 No.22
<P>We report x-ray absorption spectroscopy and x-ray magnetic circular dichroism measurements as well as multiplet calculations for Dy, Ho, Er, and Tm atoms adsorbed on Pt(111), Cu(111), Ag(100), and Ag(111). In the gas phase, all four elements are divalent and we label their 4f occupancy as 4f(n). Upon surface adsorption, and depending on the substrate, the atoms either remain in that state or become trivalent with 4f(n-1) configuration. The trivalent state is realized when the sum of the atomic correction energies (4f -> 5d promotion energy E-fd + intershell coupling energy delta E-c) is low and the surface binding energy is large. The latter correlates with a high substrate density of states at the Fermi level. The magnetocrystalline anisotropy of trivalent RE atoms is larger than the one of divalent RE atoms. We ascribe this to the significantly smaller covalent radius of the trivalent state compared to the divalent one for a given RE element. For a given valency of the RE atom, the anisotropy is determined by the overlap between the spd states of the RE and the d states of the surface. For all investigated systems, the magnetization curves recorded at 2.5 K show absence of hysteresis indicating that magnetic relaxation is faster than about 10 s.</P>
Excited Spin-State Trapping in Spin Crossover Complexes on Ferroelectric Substrates
Wä,ckerlin, Christian,Donati, Fabio,Singha, Aparajita,Baltic, Romana,Decurtins, Silvio,Liu, Shi-Xia,Rusponi, Stefano,Dreiser, Jan American Chemical Society 2018 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.122 No.15
<P>We have studied thin films of Fe(II) spin crossover complexes deposited on differently poled ferroelectric PMN-PT ([Pb(Mg<SUB>1/3</SUB>Nb<SUB>2/3</SUB>)O<SUB>3</SUB>]<SUB>1-<I>x</I></SUB>[PbTiO<SUB>3</SUB>]<SUB><I>x</I></SUB>, <I>x</I> = 0.32) substrates by X-ray absorption spectroscopy. The X-ray spectra reveal the temperature-driven conversion between high-spin and low-spin states without any observable effect of the ferroelectric polarization on the spin state of the molecules down to 100 K. In the soft X-ray-induced excited spin-state trapping (SOXIESST) regime at 3 K, large differences occur between the two ferroelectric polarizations. The efficiency of X-rays in exciting the molecules to the high-spin state is more than an order of magnitude larger when the ferroelectric dipoles of the substrate are pointing toward the surface compared to the opposite polarization. We explain our findings by a modulation of the polarization-dependent efficiency of the scattering of X-ray-generated secondary electrons at the molecules. Our results provide a deep insight into the SOXIESST mechanism and suggest that such molecules could be used as detectors for electrons traveling in the substrate at energies lower than the substrate electron affinity.</P> [FIG OMISSION]</BR>
Erbium on MgO(100)/Ag(100) as candidate for single-atom-qubit
Stefano Reale,Jiyoon Hwang,Jeongmin Oh,Aparajita Singha,Safa L. Ahmed,Denis Krylov,Luciano Colazzo,Christoph Wolf,Carlo S. Casari,Alessandro Barla,Edgard Fernandes,Francois Patthey,Marina Pivetta,Stef 한국자기학회 2023 한국자기학회 학술연구발표회 논문개요집 Vol.33 No.1