Exchange and hyperfine fields acting on dilute 153Eu In SmCo 5, Sm 2(Co 1-xFe x) 17 and Sm 2Co xM y( rmM = Fe, Cu, Zn, Zr)

Abstract

Mössbauer source experiments of dilute 153Eu and 57Fe in SmCo 5 and 153Eu in Sm 2(Co 1- x Fe x ) 17 and Sm 2 Co x M y at 4.1 K were performed. After the 153 Sm →β− 153 decay the Eu ion is trivalent and exhibits extremely large hyperfine interactions due to strong exchange fields. Since the exchange interactions are comparable to the Eu 3+ spin-orbit coupling, we calculated the expectation values of the Eu 3+ spin, magnetic hyperfine field and electric field gradient as a function of exchange field and second order crystalline field, by diagonalization of the full Hamiltonian of spin orbit, exchange and crystalline field. For SmCo 5 and Sm 2(Co 1- x Fe x ) 17 the exchange and crystalline fields are known and thus allow us to analyze our experimental results and obtain the polarized conduction electron contributions to the magnetic hyperfine field. The contribution due to magnetic neighbour polarization of conduction electrons is found to be linear in exchange field. The experimental results together with the theoretical analysis yield the Eu electric field gradient 4f Sternheimer shielding factor R Q to be 0.26±04. It is shown that Mössbauer studies of two probes ( 155Gd and Eu 3+) in magnetic systems yield directly the second order crystalline field, the exchange field and the various contributions to the hyperfine field acting on the Eu nucleus. From the experimentally measured magnetic hyperfine fields alone, approximate values for the exchange fields in the mixed systems Sm 2Co x M y were determined.