Magnetic disordered in Ti doped ErCo2 alloys: Griffiths-like behavior

Abstract

We report electrical and magnetic properties of ErCo(2−x)Tix (x=0, 0.01, 0.02, 0.03, 0.04, 0.05) in the temperature range 4–300K. The substitution of Ti for Co causes no change in the crystal structure of ErCo2 (cubic Laves phase C15 with space group Fd3¯m). The lattice parameter, a, decreases almost linearly with increasing x up to x=0.04 and then increases slightly for the largest Ti concentration. The Curie temperature, Tc is closely correlated with the lattice parameter. All resistivity curves exhibit a jump-like drop at Tc, which is the characteristic sign of the first order transition. The temperature dependence of the resistivity was analyzed using a conventional model for RCo2 alloys. We have also investigated the role of the chemical disorder in the resistivity. The temperature dependence of the resistivity and the residual resistivity vs. x are interpreted consistently, considering the existence of some Co-rich ordered regions due to the quenched-in chemical disorder. Low-field magnetization measurements were carried out in the temperature range 4–100K. The inverse susceptibility, 1/χ, shows non-linear behavior vs. temperature above Tc for all samples except ErCo2. We used three different approaches to determine the magnetic moment per formula unit: modified Curie–Weiss type paramagnetism, Néel type paramagnetism, and Griffiths-like behavior. A detailed analysis of the magnetization at low-fields reveals the complexity of the magnetic state both in the ordered and paramagnetic phases. However, the findings in the paramagnetic regime suggest that an interpretation based on the formation of a Griffiths phase is most plausible. High-field magnetization (up to 23T) was also investigated in a wide temperature range below and above Tc. In the paramagnetic regime, the magnetization data were described satisfactorily with the Landau theory. Landau coefficients a1 and a3 were determined as a function of temperature for selected samples. It was found that the coefficient a3 shows a unique behavior for all the samples, which may be attributed to a characteristic of the mixed phase (dilute magnetic ordered domains in the paramagnetic regime).