Nucleation, growth and magnetic properties of Fe ultrathin films grown on InAs(100)-4×2

Abstract We have studied the magnetic and structural properties of epitaxial BCC Fe grown at room temperature on InAs(1 0 0)-4×2 substrates using the magnetooptic Kerr effect (MOKE) in situ and scanning tunneling microscopy (STM). Growth occurs by the Volmer–Weber mode with the Fe islands nucleating in the channels between the first layer In dimer rows. With increasing Fe coverage a superparamagnetic to ferromagnetic phase transition is found to occur at a critical thickness dc of 3.5±0.05 ML consistent with a 2D percolation phase transition. The directly measured STM feature sizes are in excellent agreement with the size of the superparamagnetic islands estimated by fitting the M–H loops with a Langevin function below the critical thickness.