First-principles study of a single-molecule magnetMn12monolayer on the Au(111) surface

Abstract

The electronic structure of a monolayer of single-molecule magnets Mn 12 on a Au͑111͒ surface is studied using spin-polarized density-functional theory. The Mn 12 molecules are oriented such that the magnetic easy axis is normal to the surface, and the terminating ligands in the Mn 12 are replaced by thiol groups ͑-SH͒ where the H atoms are lost upon adsorption onto the surface. This sulfur-terminated Mn 12 molecule has a total magnetic moment of 18 B in the ground state, in contrast to 20 B for the standard Mn 12 . The Mn 12 molecular orbitals broaden due to the interaction of the molecule with the gold surface and the broadening is of the order of 0.1 eV. It is an order of magnitude less than the single-electron charging energy of the molecule so the molecule is weakly bonded to the surface. Only electrons with majority spin can be transferred from the surface to the sulfur-terminated Mn 12 since the gold Fermi level is well above the majority lowest unoccupied molecular orbital ͑LUMO͒ but below the minority LUMO. The amount of the charge transfer is calculated to be 1.23 electrons from a one-dimensional charge density difference between the sulfur-terminated Mn 12 on the gold surface and the isolated sulfur-terminated Mn 12 , dominated by the tail in the electronic distribution of the gold surface. A calculation of a level shift upon charging provides 0.28 electrons being transferred. The majority of the charge transfer occurs at the sulfur, carbon, and oxygen atoms close to the surface. The total magnetic moment also changes from 18 B to 20 B , which is due to rearrangements of the magnetic moments on the sulfur atoms and Mn atoms upon adsorption onto the surface. The magnetic anisotropy barrier is computed including spin-orbit interaction self-consistently in density-functional theory. The barrier for the Mn 12 on the gold surface decreases by 6 K in comparison to that for an isolated Mn 12 molecule.

Effects of bonding type and interface geometry on coherent transport through the single-molecule magnetMn12

“…The largest force is found at the interface between the linker molecules and the electrodes. 43 Thus, the geometry relaxation with a fixed d allows the linker molecules and the Mn 12 to relax further and lowers the force at the interface. Prior to the transport calculations, all of the geometries of the scattering region or interface geometries considered are relaxed with a fixed distance d between the electrodes, using SIESTA, until the magnitude of the maximum force exerted on the atoms becomes less than 0.1 eV/ Å, unless stated otherwise.…”

Renormalization of the tunnel splitting in a rotating nanomagnet

“…Later, beams of small magnetic clusters were investigated [7][8][9][10][11][12] and more recently free magnetic nanoparticles confined within solid nanocavities have been studied 6 . Experimentalists have also worked with molecular nanomagnets deposited on surfaces [13][14][15][16] or carbon nanotubes 17 , as well as with single magnetic molecules bridged between metallic electrodes [18][19][20][21][22] . In such experiments the particles retain some mechanical freedom.…”

Single-molecule magnetMn12on graphene

“…[13][14][15][16][17][18][19] To understand the effect of physical environment on properties of SMMs, especially that of a supporting substrate, it is desirable to place Mn 12 on well-defined surfaces and investigate the electronic and magnetic properties of individual molecules and monolayers. Much effort has already been made to deposit Mn 12 on various substrates, such as the metal Au(111), 20,21 the semi-metal Bi(111), 22 and even the ferromagnetic substrate Ni(111). 23 However, to our knowledge, first-principles methods have not been used to study hybrid nanoarchitectures consisting of SMMs (Mn 12 ) and graphitic materials.…”