Critical behavior and exchange splitting in the two-dimensional antiferromagnet Mn on Re(0001)

We investigated the temperature-dependent electronic structure of the antiferromagnetic fcc-monolayer Mn on Re(0001) using vacuum-ultraviolet momentum microscopy. At T = 25 K the collinear, row-wise antiferromagnetic phase of the Mn monolayer results in a spin splitting of states. Density-functional theory, being in good agreement with the experimental results, reveals the spin and orbital projection of the observed electronic bands. The exchange split bands shift in opposite directions with increasing temperature, decreasing the exchange splitting of a pair of itinerant bands from 280 +/- 10 meV at 25 K down to 185 +/- 10 meV at the Neel temperature T-N = 75 +/- 5 K. The exchange splitting remains constant for T > TN. The persisting exchange splitting is attributed to a remaining short-range, fluctuating antiferromagnetic order far above TN.