Magnetic disorder in Ti doped ErCo2: High-magnetic-field study

Abstract

Magnetization measurements have been carried out on ErCo(2−x)Tix (x=0, 0.01, 0.02, 0.03, 0.04, and 0.05) alloys in the temperature range of 4–300 K under high dc magnetic fields of up to 23 T. 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 shows a similar change with Ti concentration. Above TC all the studied samples show a small but unambiguous hysteresis associated with a metamagnetic transition. The observed hysteresis is attributed to the coexistence of the paramagnetic and the field-induced ferrimagnetic states. Linear temperature extrapolations of the critical fields Hc1 (where the hysteresis sets in) and Hc2 (the highest field where the hysteresis is observed) were done for each sample. Two different critical temperatures were found suggesting the existence of Co clusters. Indeed, weak negative magnetization values in low fields at low temperatures were observed for zero-field-cooling magnetic measurements. The negative magnetization is also attributed to the existence of Co clusters above TC. The spontaneous magnetization values Ms of the samples were deduced as a function of Ti concentration from the high-field data. Ms passes through a maximum for the x=0.03 sample with a maximum value of 7.15μB (6.30μB in pure ErCo2). We show how a decrease in the Er–Co antiferromagnetic exchange coupling with Ti doping may lead to such an observed maximum.