Antiferromagnetic coupling of Mn adsorbates to Fe(100)

We investigate the magnetic properties of Mn adsorbates on Fe(100) in the regime up to a few monolayers. Magnetic circular dichroism in absorption shows long-range ferromagnetic order for the Mn adsorbate, with antiferromagnetic alignment with respect to the Fe substrate. Element-specific magnetic domain imaging and hysteresis measurements show that the macroscopic magnetic behavior of the Mn adlayer is fully determined by the Fe substrate. For coverages below 0.5 ML the Mn absorption spectra show rich structures that are typical for localized $d$ states. From this the Mn ground state is identified as a mixture of atomiclike $d^5$ and $d^6$ states, with a local spin moment of $4.5{\mu }_B.$ However, the circular dichroism is 2.4 times smaller than expected for this ground state, suggesting disorder within the Mn adsorbate with an ordered moment of $1.9{\mu }_B$ at 120 K. The magnetic signal vanishes near 1 ML coverage, consistent with the theoretically predicted $c(2\mathrm{}\times 2)$ antiferromagnetic ground state of the monolayer.