Structural and magnetic properties of molecular beam epitaxy grown chromium selenide thin films

Chromium selenide thin films were grown epitaxially on $\mathrm{A}{\mathrm{l}}_{2}{\mathrm{O}}_{3}(0001)$ and Si(111)-(7 \ifmmode\times\else\texttimes\fi{} 7) substrates using molecular beam epitaxy. Sharp streaks in reflection high-energy electron diffraction and triangular structures in scanning tunneling microscopy indicate flat smooth film growth along the $c$ axis, which is very similar to that from a hexagonal surface. The x-ray diffraction pattern confirms the growth along the $c$ axis with a $c$-axis lattice constant of 17.39 \AA{}. The grown film is semiconducting, having a small band gap of about 0.034 eV, as calculated from the temperature-dependent resistivity. The antiferromagnetic nature of the film with a N\'eel temperature of about 40 K is estimated from the magnetic exchange bias measurements. A larger out-of-plane exchange bias, along with a smaller in-plane exchange bias is observed below 40 K. Exchange bias training effects are analyzed based on different models and are observed to be following a modified power-law decay behavior.