MULTIPLE MAGNETIC PHASE-TRANSITIONS, DILUTE FE HYPERFINE FIELDS AND EUROPIUM VALENCE INSTABILITIES IN RMN(2)SI(2-X)GE(X), R=RARE EARTH

Mossbauer studies of dilute Fe-57 and Eu-151 in RMn(2)Si(2-X)Ge(X) (R = La, Sm, Eu and Gd) at temperatures 4.2 K to 480 K have been performe d The diamagnetic iron and europium reveal the magnetic order of the M n and rare earth sublattices through transferred hyperfine interaction s. The Fe-57 studies show that in LaMn2Si2, LaMn2Ge2, and SmMn2Ge2 the Mn is magnetically ordered above the known Curie temperatures, and th e compounds are antiferromagnets up to T-N = 470 K 415 K and 385 K res pectively. Studies of Eu-151 in R(1-X)Eu(X)Mn(2)Si(2), (R = La, Gd) di splay Eu subspectra corresponding to Eu2+, Eu3+ and intermediate valen t Eu. All display large magnetic hyperfine fields.