A magnetic pair-breaking effect in rare earth-doped manganites

The magnetic properties of La(0.60)R(0.07)Di(0.33)MnO(3) ferromagnetic mang anites (Di = Sr, Ba) are studied, where La is partly replaced by magnetic r are earths R. It is shown that (i) there is a ferromagnetic coupling betwee n Mn and R spins, (ii) the Curie temperature is lowered compared to the par ent La compound and (iii) its depression is correlated with the effective m oment of the rare earth ion. This last relation is tentatively explained by a magnetic pair-breaking effect, where fluctuating R moments lower the dou ble-exchange coupling between Mn atoms, (C) 1998 Elsevier Science B.V.