Ternary pnictides EuCo2Pn2 (Pn = P, As) are the only representatives of the RCo2Pn2 series (R = rare earth metal) that contain divalent rare-earth ions. Unlike the rest of the series, they are also the only phases in which the Co sublattice does not exhibit magnetic ordering under ambient conditions. Nevertheless, Jeitschko et al. showed that EuCo2P2 exhibits a remarkable pressure-induced transition from localized Eu 4f magnetism to itinerant Co 3d magnetism above 3.1 GPa. Our group also showed that a similar effect can be achieved by chemical compression via the substitution of Eu for Pr in PrCo2P2. Along with the structural transformation under pressure comes an oxidation from Eu2+ to Eu3+, with an idealized reduction of the Co layers, inducing the observed magnetic changes. In this contribution we investigate the electronic structure of EuCo2P2 in both structures using a combination of experimental and theoretical methods in relation to the traditional Zintl understanding of the ThCr2Si2-type structures. We demonstrate that the traditional electron counting scheme does not adequately describe the changes in chemical bonding and electron density redistribution that takes place upon the structural phase transition in such intermetallic phases.

Revisiting bond breaking and making in EuCo2P2: Where are the electrons?

2019 Spring National Meeting

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