Effect Of Ga And Cd Substitutions On The First-Order Antiferromagnetic Transition In Ndco2zn20

The cubic neodymium-based compound NdCo2Zn20 exhibits a first-order antiferromagnetic (AFM) transition at T-N = 0.53 K. Strong magnetic fluctuations at temperatures up to 5 K were suggested by the downward curvature of the electrical resistivity rho(T) and the reduced magnetic entropy S-m of 0.5Rln2 at T-N. In this study, we measured.(T), the isothermal magnetization M(B), magnetic susceptibility.(T), and specific heat C(T) of NdCo2Zn20-xCdx for x = 1 and NdCo2Zn20-yGay for y = 1 and 2. The sharp peak of the magnetic specific heat C-m(T) at T-N for x = 0 is changed to a weak and broad maximum at 0.55 K for x = 1. This drastic change in C-m(T) suggests that the isovalent Cd substitution for Zn disorders the exchange interactions between the Nd moments to hinder the first-order AFM transition. On the other hand, C-m(T) for y = 1 and 2 exhibits a lambda-shaped anomaly, which is a characteristic of a second-order AFM transition, at elevated temperatures of 0.78 and 1.5 K, respectively. The stabilization of the AFM order by the Ga substitution indicates that 4p electron doping strengthens the AFM interaction. We therefore propose that the first-order transition in NdCo2Zn20 is maintained by competitive magnetic interactions inherent in the Nd diamond sublattice.