Magnetic phase diagram of ErGe1−xSix (0<x<1)

Abstract The composition-temperature magnetic phase diagram of ErGe 1− x Si x (0 x T N k z and ( k ' x ,0, k ' z ) with a slight deviation of k x , k ' x and k ' z from 1/2). Whatever x , an incommensurate phase appears below T N , the wavevector being (0,0, k z ) for x k ' x ,0, k ' z ) for x > 0.40. For 0.17 ≥ x ≤ 0.55, a first-order transition occurs as function of the temperature between these two phases. For x ≥ 0.65, a lock-in transition takes place at T IC , leading from the wavevector ( k ' x ,0, k ' z ) to (1/2,0,1/2), as was already observed in ErSi. Finally, for x x k z ) or ( k ' x ,0, k ' z ) respectively remain unchanged in the whole temperature range below T N . For x ≥0.65, a small amount of a magnetic phase characterized by the wavevector (0,0, 1/2) coexists with the main phases, below a Neel temperature T ' N slightly lower than T N . In all cases, the erbium magnetic moments are colinear along the orthorhombic α -axis; the arrangement of the moments in the commensurate phases is the same as in ErSi and the incommensurate orderings correspond to sine-wave amplitude modulations. A brief account on the theoretical interpretation of this phase diagram is finally given.