Large magnetic cooling power involving frustrated antiferromagnetic spin-glass state in R_2NiSi_3(R = Gd,Er)

摘要

The ternary intermetallic compounds Gd_2NiSi_3 and Er_2NiSi_3 are synthesized in chemically single phase, which are characterized using dc magnetization, ac magnetic susceptibility, heat capacity, and neutron diffraction studies. Neutron diffraction and heat capacity studies confirm that long-range magnetic ordering coexists with the frustrated glassy magnetic components for both compounds. The static and dynamical features of dc magnetization and frequency-dependent ac susceptibility data reveal that Gd_2NiSi_3 is a canonical spin-glass system, while Er_2NiSi_3 is a reentrant spin cluster-glass system. The spin freezing temperature merges with the long-range antiferromagnetic ordering temperature at 16.4 K for Gd_2NiSi_3. Er_2NiSi_3 undergoes antiferromagnetic ordering at 5.4 K, which is slightly above the spin freezing temperature at 3 K. The detailed studies of nonequilibrium dynamical behavior, viz., the memory effect and relaxation behavior using different protocols, suggest that both compounds favor the hierarchical model over the droplet model. A large magnetocaloric effect is observed for both compounds. Maximum values of isothermal entropy change (-ΔS_m) and relative cooling power (RCP) are found to be 18.4 J/kg K and 525 J/kg for Gd_2NiSi_3 and 22.6 J/kg K and 540 J/kg for Er_2NiSi_3, respectively, for a change in field from 0 to 70 kOe. The values of RCP are comparable to those of the promising refrigerant materials. A correlation between large RCP and magnetic frustration is discussed for developing new magnetic refrigerant materials.