Growth, structure, and magnetic properties of epitaxialNixMn100−xsingle layers andCo/NixMn100−xbilayers onCu3Au(100)

Abstract

The growth and structure of single-crystalline ultrathin ${\text{Ni}}_{x}{\text{Mn}}_{100\ensuremath{-}x}$ films on ${\text{Cu}}_{3}\text{Au}(100)$, and also the magnetic properties of Co ultrathin films on ${\text{Ni}}_{x}{\text{Mn}}_{100\ensuremath{-}x}/{\text{Cu}}_{3}\text{Au}(100)$ have been investigated by x-ray photoelectron and Auger electron spectroscopy, low-energy electron diffraction, reflection high-energy electron diffraction, and magneto-optical Kerr effect (MOKE). For the investigated concentration range $(10\ensuremath{\le}x\ensuremath{\le}77)$, our results reveal good epitaxial layer-by-layer growth at a substrate temperature of 300 K. A weak $c(2\ifmmode\times\else\texttimes\fi{}2)$ superstructure was observed at the surface of all NiMn films. The average perpendicular interlayer spacing of the NiMn alloy films decreases from $1.88\text{ }\text{\AA{}}$ at $x=10$ to $1.69\text{ }\text{\AA{}}$ at $x=77$. The lattice parameters of equiatomic NiMn films were determined to be $3.52\text{ }\text{\AA{}}$ perpendicular to the sample surface and $3.76\text{ }\text{\AA{}}$ in the sample plane, indicating a face-centered tetragonal (fct) structure as expected for the $L{1}_{0}$ NiMn phase with the $c$ axis along the film normal (``$c$-axis growth''). For the Co/NiMn bilayers $(23\ensuremath{\le}x\ensuremath{\le}55)$, MOKE hysteresis loops show a thickness-independent coercivity, suggesting no magnetic coupling at the Co/NiMn interface. Although the structural results indicate the formation of fct NiMn in the equiatomic concentration range, we have no indication of antiferromagnetism for the NiMn films epitaxially grown on ${\text{Cu}}_{3}\text{Au}(100)$ at room temperature. This is contrary to the observations on $\text{Co}/{\text{Ni}}_{50}{\text{Mn}}_{50}$ bilayers on Cu(100), where ``$a$-axis growth'' of NiMn occurs.