Magnetic frustration driven by conduction carrier blocking in Nd2Co0.85Si2.88

The intermetallic compound Nd2Co0.85Si2.88 having a triangular lattice could be synthesized in single phase only with defect crystal structure. Investigation through different experimental techniques indicate the presence of two magnetic transitions in the system. As verified experimentally and theoretically, the high-temperature transition TH similar to 140 K is associated with the development of ferromagnetic interaction between itinerant Co moments, whereas the low-temperature transition at TL similar to 6.5 K is due to the coupling among Nd-4f and Co-3d moments, which is antiferromagnetic in nature. Detailed studies of temperature-dependent dc magnetic susceptibility, field dependence of isothermal magnetization, nonequilibrium dynamical behavior, viz., magnetic relaxation, aging effect, magnetic-memory effect, and temperature dependence of heat capacity, along with density functional theory (DFT) calculations, suggest that the ground state is magnetically frustrated spin glass in nature, having competing magnetic interactions of equivalent energies. DFT results further reveal that the 3d/5d-conduction carriers are blocked in the system and act as a barrier for the 4 f-4 f RKKY interactions, resulting in spin frustration. Presence of vacancy defects in the crystal are also conducive to the spin frustration. This is an unique mechanism of magnetic frustration, not emphasized so far in any of the ternary R2TX3 (R = rare earth, T = transition elements, and X = Si, Ge, In) type compounds. Due to the competing character of the itinerant 3d and localized 4 f moments, the compound exhibits anomalous field dependence of magnetic coercivity. The system also exhibits a considerable magnetic entropy change of -ASM similar to 13.3 J/kg K with a relative cooling power (RCP) of 220 J/kg and adiabatic temperature change ATad of 6 K for magnetic field change of 70 kOe.

Automated summary

The intermetallic compound Nd2Co0.85Si2.88 with a triangular lattice exhibits single-phase synthesis only with a defective crystal structure. The system undergoes two magnetic transitions, with a high-temperature transition at around 140 K associated with a ferromagnetic interaction between itinerant Co moments, and a low-temperature transition at around 6.5 K due to the coupling between Nd-4f and Co-3d moments, which is antiferromagnetic in nature. Detailed investigations and density functional theory calculations suggest that the ground state of the compound is a magnetically frustrated spin glass with competing magnetic interactions of equal energies.