Magnetic properties and surface structure of ultrathin Fe/Ir(111) films have been investigated using the surface magneto-optic Kerr effect and low-energy electron diffraction. Layer-by-layer growth of Fe/Ir(111) is observed for the first three monolayers at room temperature. For Fe thinner than three monolayers, pseudomorphic growth of Fe films is observed. The layer distance is close to that of
fcc(111) Fe. For Fe thicker than three monolayers, the surface structure can be identified to be related to the bcc(110) arrangement of Fe atoms in Kurdjumov-Sachs orientation. As the Fe thickness increases, the linear increase of the Kerr intensity is observed. The Kerr intensity comes from the bcc-Fe and a thin magnetic dead layer is observed at the interface.
The magnetic properties and surface structure of ultrathin Fe/Ir(111) films after high temperature annealing treatment have also been investigated. The Fe atoms diffuse into the Ir(111) substrate to be a FexIr1-x alloy as annealing temperature increases. For annealing temperature between 750 K and 800 K, there is a blocking of the interdiffusion behavior for Fe atoms into the Ir(111) substrate and the existence of the specific concentration of Fe of the FexIr1-x interface alloy which shows a stable state at this annealing temperature region. Combining the experimental results of Auger analysis, LEED patterns and the theoretical calculations, one can conclude that the specific concentration of Fe of the FexIr1-x interface alloy at the stable state is Fe0.5Ir0.5 as annealing temperature between 750 K and 800 K. For 5~9 ML Fe/Ir(111) films, a layered structure of Fe/FexIr1-x/Ir(111) could be obtained after high temperature annealing treatment. The surface of this layered structure becomes flatter after the high temperature annealing treatment. The structure of the top Fe films can be identified to be related to the bcc(110) arrangement of Fe atoms in Kurdjumov-Sachs orientation, however, strained by the underneath Fe0.5Ir0.5 interface alloy since this interface alloy is also strained by Ir(111) substrate which leads to the change of the lattice parameter of the unit cell of Fe bcc(110) at the surface from 0.248 nm to 0.272 nm. The surface structure transition between the KS orientation to strained KS orientation for 5~9 ML Fe/Ir(111) at annealing temperature from 300 K to 700 K have also been investigated. For annealing temperature less than 550 K, the KS orientation shows low periodicity. The periodicity of this KS orientation gets better as annealing temperature increases and become stable as annealing temperature larger than 700 K. Finally, the structural, compositional and magnetic phase diagram of Fe/Ir(111) is constructed. For Fe film thinner than 3 ML at annealing temperature between 300 K and 900 K, no Kerr intensity is observed due to the fcc arrangement of Fe films and FexIr1-x alloy. For Fe films thicker than 3 ML, Kerr intensity could be observed owing to the bcc arrangement of Fe films. The coercivity and saturation magnetization enhanced abruptly (higher than Fe/Pt(111) system) after the high temperature annealing treatment which is because of the compositional and structural change of this system.

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