Annealing-induced extension of the antiferromagnetic phase in epitaxial terbium metal films

The temperature range of helical antiferromagnetic (AFM) order in epitaxially grown Tb metal films on W(110) was studied via ac susceptibility using the magneto-optical Kerr effect. The temperature range of the AFM phase was found to get wider with increasing annealing temperature, reaching a maximum width of 17 K when the film is annealed at T-an=1200 K. This shows that the AFM phase is stabilized in epitaxial films as compared to bulk Tb metal. Annealing-induced changes of the surface topography of the films were monitored by scanning tunnel microscope and low-eneregy electron diffraction, revealing a statistical surface roughness for T-an < 600 K and the formation of large terraces separated by monatomic steps for 600 K < T-an < 800 K. Annealing above approximate to 800 K results in step bunching, followed by a breakup of the film for T-an>1000 K. Both the extension of the AFM phase in the film and the annealing-induced changes of the surface topography can be explained by assuming the presence of a reconstructed Tb monolayer at the film-substrate interface that serves as an effective substrate on which a slightly strained Tb film lattice is stabilized upon annealing.