Reentrant spin-glass behavior induced by the frustration of Fe-Fe interactions in Laves phase Nb1−xHfxFe2 alloys

We carried out magnetization and specific-heat measurements of metallic compounds Nb1−xHfxFe2 (x = 0 and 0.65), which exhibit reentrant spin-glass freezing. The frequency dependence of ac susceptibility and the bifurcation between zero-field-cooled and field-cooled magnetization curves suggest the complex coexistence of magnetic phases at low temperatures. A long-time relaxation of magnetization is possibly due to the cluster-type and traditional reentrant spin-glass transition, which may be induced by the frustration of long-range Fe-Fe interactions. We did not observe any discontinuity indicating long-range magnetic phase transition in the data of specific heat versus temperature, but a broad hump characteristic of spin-glass freezing. The difference between the behaviors of two samples proves the existence of two types of reentrant spin-glass in alloys. The moment arrangements are briefly discussed.