Eu11Zn4SnAs12 is a new addition to the family of transition metal Zintl compounds. It crystallizes in a new structure type consisting of alternately packed Eu layers between an anionic [Zn2As3]5− sheet and layers made of parallel isolated pillars of ethane-like [Sn2As6]12− species. To maintain the electron count, all the Eu sites can be assumed as Eu2+ while Zn, Sn, and As sites can be assigned oxidation states of +2, +3, and − 3, respectively. Quantum chemical calculations show that the ethane-like units can be considered as consisting of covalent single bonds; however, the [Zn2As3]5− sheets are best described with delocalized bonding and there is evidence of Eu−As interactions. The measurements of magnetic properties confirm that all the Eu ions are Eu2+, consistent with the Zintl formalism. Eu11Zn4Sn2As12 is paramagnetic above 15 K with ferromagnetic ordering below 15 K. The magnetic ordering is accompanied by a decrease in resistivity and the compound exhibits large negative CMR with a maximum reduction at 15 K, 3 orders of magnitude or 2689-fold reduction at 9 T. Eu11Zn4Sn2As12 has unique magnetic properties, namely, the lack of saturation at 7 T, and the onset of magnetoresistance is exhibited at temperatures significantly higher than the ordering temperature. In order to probe the magnetic and transport properties, the alloy Eu11−xSrxZn4Sn2As12 with Sr2+ to replace Eu2+ has been prepared. The synthesis, crystal structures, and properties of Eu11−xSrxZn4Sn2As12 will be presented and discussed.

New Zintl phases featuring a layered structure with ferromagnetic ordering and negative magnetoresistance

2019 Spring National Meeting

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