Program Highlights

Structural and Magnetic Evolution of Bimetallic MnAu Clusters

Xiao Cheng Zeng, Jeffrey Shield, and David Sellmyer
Nebraska MRSEC

He Kai
Brookhaven National Laboratory

Matthew J. Kramer
Ames National Laboratory

Highly-symmetrized MnAu nanoalloys may possess high magnetic moments for potential application. The magnetic properties of MnAu nanoclusters exhibit strong dependence on the cluster sizes and morphologies. Determining the most stable morphologies as well as their spin-polarization patterns is important for their further application.  Researchers at University of Nebraska MRSEC in collaboration with researchers at Brookhaven and Ames Laboratory performed a joint theoretical/experimental study to investigate structural and magnetic evolution of MnAu clusters (Nano Letters 14, 1362 (2014)). They found the MnAu clusters order into the L10 structure, and monotonic size-dependences develop for the composition and lattice parameters, which are well reproduced by the density functional theory calculations by the theoretical group. Simultaneously, Mn diffusion forms 5 Å nanoshells on larger clusters inducing significant magnetization in an otherwise antiferromagnetic system. The differing atomic mobilities yield new cluster nanostructures that can be employed generally to create novel physical properties. This study shows the first case of utilizing the different mobilities of atoms in a solid matrix as a driving force for nanoscale nanoparticle engineering. By adding small/meta-stable clusters of desirable compositions to the initial cluster ensemble, nanoparticles with complex heterostructures can be built up layer by layer. These techniques create potentially powerful strategies to fabricate unique nanoscale heterostructures by modifying preformed nanoparticles.

These programs are supported by the National Science Foundation, Division of Materials Research, Materials Research Science and Engineering Program, Grant 0820521.

Top: Transmission electron microscopy (TEM) images of as-produced (left) and annealed (right) MnAu clusters. The insets show the size distributions. Bottom: Representative TEM images for annealed MnAu clusters with various sizes.