First-principles calculation on the Curie temperature of Gd3NiSi2

The electronic structure and magnetic properties for Gd3NiSi2 have been studied theoretically from a first-principles density functional calculation. The energy band structure is calculated in a local spin density approximation (LSDA), and in a LSDA + Hubbard U approach (LSDA + U), respectively. For Gd atoms, in the LSDA + U approximation, seven spin-up 4f bands are fully occupied and situated at the bottom of Si s states, while the spin-down 4f hole levels are completely unoccupied and well above the Fermi level. The calculated magnetic moments for the three Gd sites vary from 7.13 to 7.16 mu(B), leading to a total magnetization of 21.5 mu(B) per formula unit including the small induced moments at Ni and Si atoms. The exchange coupling parameters for the nearest Gd-Gd pairs (J(Gd-Gd)) are 0.16 mRyd, 0.14 mRyd and 0.19 mRyd in the three Gd sub-lattices, respectively. The inter-site distance dependence of JGd-Gd shows a RKKY-like oscillation. The estimated Curie temperature is about 251 K from the calculated exchange coupling parameters based on the mean-field approximation, in good agreement with the experimental value (T-C(exp.) = 215 K).