Comparison of the crystalline structure, morphology, and magnetic properties ofγ-phaseMn∕Cu3Au(100)ultrathin films by varying the growth temperature

Abstract

The structural and magnetic properties of room-temperature (RT: $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$)-grown and low-temperature (LT: $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$)-grown $\mathrm{Mn}∕{\mathrm{Cu}}_{3}\mathrm{Au}(100)$ thin films were investigated. Mn films deposited at RT and LT demonstrate very different behaviors in the crystalline structure, morphology, and magnetism. $\mathrm{RT}\text{\ensuremath{-}}\mathrm{Mn}$ films reveal apparent layer-by-layer growth for $0--2\phantom{\rule{0.3em}{0ex}}\mathrm{ML}$ (monolayer) followed by reduced oscillations. Although the medium-energy electron diffraction (MEED) oscillation is reduced, the intensity of specular spot increases monotonically after $6--7\phantom{\rule{0.3em}{0ex}}\mathrm{ML}$, inferring the tendency of smooth morphology. The study of scanning tunneling microscopy also shows that even in $19\phantom{\rule{0.3em}{0ex}}\mathrm{ML}$ $\mathrm{Mn}∕{\mathrm{Cu}}_{3}\mathrm{Au}(100)$, the surface morphology is composed of large terraces with the size up to hundreds of nanometers. The $\mathrm{LT}\text{\ensuremath{-}}\mathrm{Mn}$ films reveal apparent layer-by-layer growth for $0--5\phantom{\rule{0.3em}{0ex}}\mathrm{ML}$ followed by the reduced oscillations, and then the MEED intensity remains at low intensity, inferring the rough surface. The RT- and $\mathrm{LT}\text{\ensuremath{-}}\mathrm{Mn}$ films exhibit a thickness-dependent structural transition from a face-centered cubic to a face-centered tetragonal structure at different critical thicknesses, $\ensuremath{\sim}12--14$ and $\ensuremath{\sim}8\phantom{\rule{0.3em}{0ex}}\mathrm{ML}$, respectively. Significant exchange bias is observed in $\mathrm{Fe}∕\mathrm{RT}\text{\ensuremath{-}}\mathrm{Mn}$ bilayers. It increases monotonously with Mn thickness. The exchange bias coupling in $\mathrm{Fe}∕\mathrm{LT}\text{\ensuremath{-}}\mathrm{Mn}$ is much weaker than $\mathrm{Fe}∕\mathrm{RT}\text{\ensuremath{-}}\mathrm{Mn}$ and drastically varies with Mn film thickness. The presence of exchange bias in the $\mathrm{Fe}∕\mathrm{Mn}$ bilayers also indicates the antiferromagnetism of $\ensuremath{\gamma}$-phase $\mathrm{Mn}∕{\mathrm{Cu}}_{3}\mathrm{Au}(100)$.