PRESSURE-INDUCED TRANSITION OF THE SUBLATTICE MAGNETIZATION IN EUCO2P2 - CHANGE FROM LOCAL MOMENT EU(4F) TO ITINERANT CO(3D) MAGNETISM

Antiferromagnetism in EuCo2P2 (ThCr2Si2-type structure) is due to orde ring of the Eu2+(S-8(7/2)) sublattice moments (T-N = 66.5 K) while the Co(Sd) sublattice does not carry any magnetic moment. EuCo2P2 undergo es a pressure-induced isostructural phase transition at p(c) = 3.1 GPa . Eu-151 high-pressure Mossbauer experiments (0 less than or equal to p less than or equal to 5 GPa) reveal a valence transition of Eu from Eu2+ to nonmagnetic Eu3+(F-7(0)) at p > p(c) with the consequence that the disappearance of the Eu(4f) sublattice magnetism is accompanied b y a simultaneous appearance of Co(3d) sublattice magnetism (T-N = 260 K). The latter is explained by the filling of the 3d states.