Reversible phototuning of the large anisotropic magnetization at the interface between a self-assembled photochromic monolayer and gold.

We have observed the emergence of a large anisotropic magnetization and significant photoinduced changes in the magentization that appear at the interface between a gold film and an azobenzene-containing self-assembled monolayer. The magnetization value was extremely high, up to 50 mu(B) per adsorbed molecule. These photomagnetic effects can be attributed to a photoinduced change in the loss of d charge due to photoisomerization of the azobenzene monolayer, which is accompanied by inversion of the surface dipoles. Furthermore, we have also observed reversible changes in the work function of the gold film by alternating UV and visible light, showing that the value of the surface dipole moment is changed as a result of photoisomerization. This allowed us to control the magnetization by alternating the photoillumination between UV and visible light, and we have clarified the mechanism for these photomagnetic effects. A novel strategy such as this, which enables significant reversible phototuning of the magnetic order, has great potential for applications in future magneto-optical devices.