From Magnetic Nanowires to 2D Layer Zintls by Topotactic Exchange

The Zintl compounds comprise a vast and versatile, constantly growing family of newly emerging materials, normally based on a binary semiconductor and a rare earth atom in particular Europium. Eu₃In₂P₄ and Eu₃InP₃ were suggested to be an example of materials with new magnetic Zintl phases already 20 years ago [1]. Recently, a vast selection of newly emerging compounds, particularly those based on InAs with the addition of strontium, barium or europium – such as Eu₃In₂As₄ – have been included into the Zintl family of materials and widely studied [2, 3]. Extensively conducted research showed a large variety of unique magnetic, electronic, and topological properties both in bulk and layers of Zintl materials. In view of its potential, we incorporated a Europium source in our III-V MBE system assigned for the growth of III-V nanowires by gold assisted vapor liquid solid (VLS) growth. Our study focused on the growth of Europium containing shells on Wurtzite or Zinc Blende InAs NWs. Which showed interesting magnetic properties measured by both SQUID and MPMS.

We found that a unique ZB-like mosaic structure forms when Eu, In and As are all evaporated on the pre-grown InAs nanowires at the same time. Interestingly, Eu ions produce inversion domain boundaries (IDBs), inducing a flip of the InAs lattice, similar to what has been reported in bulk-Zintl EuIn₂As₂. The Eu atoms are situated along the three {111} planes forming a prismatic structure.

However, when no In is provided during the shell growth an exchange reaction between the In and the Eu takes place via the Arsenic framework. Thus, the InAs nanowires are gradually converted into Eu₃In₂As₄ Zintl nanowires with an orthorhombic crystal structure, as long as the original nanowires have a wurtzite structure.

We found that when this process is repeated on zinc blende wires rather than wurtzite ones Eu₅In₂As₆ Zintl nanowires formed using the unconventional exchange reaction thereby Europium and Indium are again mutually exchanged by a similar mechanism. We thus present the formation of a Zintl phases obtained for the first time in nanowires form. Given the zinc blende structure of such nanowires it occurred to us that the same process can be carried out on a zinc blende InAs substrate which indeed produced an Eu₅In₂As₆ Zintl 2D layer. We followed this unique and newly observed process on a variety of substrates, to produce a variety of Zintl phase 2D layers which have fascinating properties and will be demonstrated in this talk.

The properties of these nanowires, including their composition, crystal structure and magnetic order, were characterized by studying the as grown nanowires and epilayers as well as FIB produced lamellae from the 2D layers.

[1]  J. Jiang, A.C. Payne and S. M. Kauzlarich, MRS Proceedings 848, 131 (2004).
 [2] A. B. Child, S. Baranets and S. Boven, J. Solid State Chem. 278, 120889 (2019).
 [3] M. S. Song, L. Houben and Y. Zhao, et. al., Nature Nano. 19, 1796 (2024).