Unexpected modification of magnetic properties by Y substitution in Eu₂PdSi₃

Abstract

The results of dc and ac magnetization, magnetic relaxation, electrical resistivity (ρ) and heat-capacity (C) measurements on Eu₂PdSi₃ and its Y-substituted alloys, Eu_2−xY_xPdSi₃(x=0.5 and 1.5), crystallizing in a AlB₂-derived hexagonal structure, are reported. The parent Eu compound has been found by us to show two magnetic transitions, at 40 and 10 K, arising from Eu sites (called 2b and 6h sites, respectively) with two different chemical surroundings. While the available data for the parent compound suggest the existence of long-range magnetic ordering below these temperatures, partial Y substitution brings out interesting changes in the magnetic properties. For instance, for an initial replacement of Eu by Y (x=0.5 alloy), (i) the low-temperature divergence of zero-field-cooled (ZFC) and field-cooled magnetic susceptibility (χ) sets in at a much higher temperature, compared to that in x=0.0. (ii) The temperature-dependent χ and C are considerably broadened at low temperatures, compared to those in the parent compound; apparently, the features due to onset of magnetic ordering from the 2b site become more prominent in these bulk measurements by Y substitution. (iii) The hysteresis curves reveal a nonzero remanent magnetization in the magnetically ordered state for the Y-substituted alloys, unlike in the parent compound. (iv) Isothermal remanent magnetization (M_IRM) undergoes a slow relaxation with time at low temperatures, while, for x=0.0, it falls to zero immediately after the field is switched off. (v) Interestingly, there is a sudden drop in the ZFC M_IRM at 5 K about 10 min after the field is switched off while undergoing slow relaxation with time. Thus, Y substitution for Eu brings out peculiar changes in the magnetic properties of Eu₂PdSi₃ and appears to favor metastability in the magnetic response, presumably due to magnetic disorder in such substituted alloys.