First-order magnetic phase transition in (Er, Tb)M2(M=Co, Ni) (abstract)

Abstract

The rare-earth intermetallic compounds RCo2, cubic Laves phases, are very suitable to study the magnetism of the 3d. Depending on the R magnetism we have an induced moment for the Co. For R=Dy, Ho, or Er the magnetic transition is of first order, whereas for Gd and Tb it is of second order. This behavior has been observed in this work by electrical resistivity and dc magnetization measurements in function of concentration in the system Er1−xTbx)Co2 where the internal field of the nearest R neighbors can induce the Co moment. Magnetization measurements of field cooling (FC) and zero field cooling (ZFC) samples are different for T<Tc. This difference collapses for higher applied magnetic fields. The minimum for T just above Tc in ρ vs T curves disappears for x=0.2 with the onset of the second-order transition up to x=1.0. This minimum can result from the conduction electrons scattering on the spin fluctuations, enhanced by the 4f moments and the scattering by phonons. The idea of the metamagnetism of Co moments in the origin of this minimum is discarded. From our results we can conclude that a small amount of Tb in ErCo2 changes the first-order to second-order transition. Since the localization of the Fermi energy in the density of state of the 3d band is very important, a comparison study has been done with the system Er1−xTbx)Ni2. The concentration dependence of the lattice parameter differs a little from Vegard’s law. Here we can infer from our results that all the magnetic transitions are second-order type.