Interplay between structural, electronic, and magnetic instabilities in EuT2P2 (T = Fe, Co) under high pressure

Eu-151 (and Fe-57) high-pressure Mossbauer investigations on EuFe2P2 reveal that the pressure-induced isostructural phase transition 3 less than or equal top less than or equal to9 GPa is accompanied by a continuous valence transition from Eu2+ to Eu3+ with the consequence of the disappearance of the Eu(4f) sublattice moment. However, contrary to EuCo2P2 we find in the high-pressure phase of EuFe2P2 no magnetic moment on Fe. Volume-dependent band-structure calculations in both systems show that the formation of the 3d moment strongly depends on the position of the 3d states relative to the Fermi energy and that the filling of the 3d states in EuCo2P2 is mainly caused by the P-3p electrons.