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Chromium is an itinerant antiferromagnet with a Neel temperature of 311K. Bulk Cr has an inconmensurate spin-density wave, and a spin-reorientation transition at low temperature. Thin films of Cr show a range of behaviors, which have been exploited for applications in giant magnetoresistance, spin-valves and spintronic devices. However, there are surprisingly few structural studies of Cr films a few layers thick. This deficiency exists even though thin Cr films are frequently used as surrogates in surface science because bulk crystals are difficult to clean.
Here we thoroughly characterize the structure of one, two and three Cr layers on W(110), and also of thick Cr(110), using diffraction and ab-initio calculations. Experimental structures were determined from multiple-scattering simulations of low-energy electron diffraction data obtained from micron-sized areas using a low-energy electron microscope. The first-principles DFT calculations indicate that the first few layers of Cr on W(110) should be antiferromagnetically ordered. The magnetic moment of the Cr in these pseudomorphic films under tensile strain is generally enhanced over those in bulk Cr because of the increased volume per atom. The magnetic moment of top layer Cr atoms is highest at 2.5-2.7 that of bulk Cr. By comparing the experimental structures to theory, we will discuss the magnetic state of ultra-thin Cr films. The experiment-theory comparison also puts to test the ability of DFT to predict the energetics of surface wetting. |