Itai Carmeli

Magnetism induced by the organization of self-assembled monolayers

Unique occurrence of magnetism is shown, in which magnetism appears ex nihilo, when organic molecules are self-assembled as monolayers on gold substrate. The molecules as well as the substrate, when they stand alone, are diamagnetic. Using a superconducting quantum interference device type magnetometer we obtained direct evidence that close-packed organized thio-organic films adsorbed on gold substrates possess magnetic properties at room temperature. The films studied show very high specific magnetization, up to many tens Bohr magnetons per adsorbed molecule, with a very small hysteresis. It is highly anisotropic and shows almost no temperature dependence. The magnetism observed is related to charge transfer between the organic layer and the metal substrate. Yet, the uniqueness here is that many spins are polarized per adsorbed molecules. The magnetic effect is related to the two dimensional organization of the organic molecules on the metal substrate which might explain the high anisotropy.

Molecular enhancement of ferromagnetism in GaAs∕GaMnAs heterostructures

The authors investigate effects of chemisorption of polar organic molecules onto ferromagnetic GaAs∕GaMnAs heterostructures. The chemisorbed heterostructures exhibit striking anisotropic enhancement of the magnetization, while GaAs substrates that are physisorbed with the same molecules show no change in magnetic properties. Thus the enhanced magnetism of the chemisorbed heterostructures reflects changes in spin alignment that arise from surface bonding of the organic monolayer.

New electronic and magnetic properties of monolayers of thiols on gold

New electronic and magnetic properties are induced by the adsorption of close-packed monolayers of thiols on gold. In layers made from chiral molecules, unexpectedly large electronic dichroism is observed, which manifests itself as spin-specific electron transmission. For many thiolated molecules self-assembled on gold, a surprisingly large ferromagnetism is observed. All the observations can be rationalized by assuming orbital ferromagnetism of the organic thin layer. This is a new type of magnetism, induced by the formation of a closed packed layer of organic molecules on metal. The adsorption results in charge transfer between the substrate and the adsorbed layer, which is the origin of this magnetism.

Electronic‐Magnetic Properties of Monolayers of Chiral Bio‐organic Molecules

Measurements of the spin‐correlated transmission of electrons through organized monolayers of polypeptide helices, absorbed on gold substrate, show high spin selectivity. The direction of the magnetic moment of the layer depends on the handedness of the helix molecule and on the direction of their dipole moment with respect to the metal substrate.