Exchange Interaction of Strongly Anisotropic Tripodal Erbium Single-Ion Magnets with Metallic Surfaces

Abstract

We present a comprehensive study of Er(trensal) single-ion magnets deposited in ultrahigh vacuum onto metallic surfaces. X-ray photoelectron spectroscopy reveals that the molecular structure is preserved after sublimation, and that the molecules are physisorbed on Au(111) while they are chemisorbed on a Ni thin film on Cu(100) single-crystalline surfaces. X-ray magnetic circular dichroism (XMCD) measurements performed on Au(111) samples covered with molecular monolayers held at temperatures down to 4 K suggest that the easy axes of the strongly anisotropic molecules are randomly oriented. Furthermore XMCD indicates a weak antiferromagnetic exchange coupling between the single-ion magnets and the ferromagnetic Ni/Cu(100) substrate. For the latter case, spin-Hamiltonian fits to the XMCD M(H) suggest a significant structural distortion of the molecules. Scanning tunneling microscopy reveals that the molecules are mobile on Au(111) at room temperature, whereas they are more strongly attached on Ni/Cu(100). X-ray photoelectron spectroscopy results provide evidence for the chemical bonding between Er(trensal) molecules and the Ni substrate. Density functional theory calculations support these findings and, in addition, reveal the most stable adsorption configuration on Ni/Cu(100) as well as the Ni–Er exchange path. Our study suggests that the magnetic moment of Er(trensal) can be stabilized via suppression of quantum tunneling of magnetization by exchange coupling to the Ni surface atoms. Moreover, it opens up pathways toward optical addressing of surface-deposited single-ion magnets.

4f occupancy and magnetism of rare-earth atoms adsorbed on metal substrates

“…1) are in very good agreement with the spectra simulated for the 4f 11 configuration as well as with previous reports for trivalent Er [30,51]. The relative amplitudes of the multiplet peaks within the M 5 edge vary with the substrate due to the presence of a different ligand environment.…”

Giant Hysteresis of Single‐Molecule Magnets Adsorbed on a Nonmagnetic Insulator

“…These values vastly exceed the corresponding records reported for any surface-adsorbed SMM [4][5][6][7][8][9][10][11][12][13]26 ] as well as the ones reported for bulk TbPc 2 . [ 20 ] The large remanence indicates that quantum tunneling of magnetization is strongly suppressed for fi elds below 3 T, with only a very subtle modulation of the relaxation rate across the hysteresis loop.…”

“…Overall, the detailed knowledge on TbPc 2 makes it an ideal candidate to test if a tunnel barrier can boost the magnetic properties of surface-adsorbed SMMs. In this communication we show that the magnetic remanence and hysteresis opening obtained with TbPc 2 on MgO tunnel barriers outperform the ones of any other surface-adsorbed SMM [4][5][6][7][8][9][10][11][12][13]26 ] as well as those of bulk samples of TbPc 2 . [ 20 ] The scanning tunneling microscopy (STM) images in Figure 1 b,c show that TbPc 2 self-assembles by forming perfectly ordered 2D islands on two monolayers (MLs) of MgO on Ag(100).…”

Molecular lanthanide single-ion magnets: from bulk to submonolayers

“…Out of the Ln(trensal) family [58,108,110,111], the Er(trensal) SIM was studied in the monolayer regime on Au (1 1 1) and Ni/Cu(1 0 0) surfaces [180]. The shape of the ligand is tripodal with the three legs being linked at an apex nitrogen atom as described in section 4.2.…”