Atomic structure of the (111) surface of the antiferromagnetic 1/1 Au-Al-Tb approximant

The recently discovered antiferromagnetic 1/1 Au-Al-Tb approximant exhibits a whirling spin order oriented along the [111] direction. Here we report an investigation of the atomic structure of the (111) surface by scanning tunneling microscopy and density functional theory (DFT) calculations. Scanning tunneling microscopy reveals a Tb-terminated step-terrace morphology, with step heights appearing to minimize the number of broken bulk icosahedra. The atomic structure of the terraces is bias dependent, with Tb atoms imaged under positive bias and Au/Al atoms under negative bias. The surface is found to reconstruct, with the Au/Al atoms producing a linear row structure, an example of a surface reconstruction in a Tsai-type system. These observations are confirmed by DFT calculations.