Dong Jian-Min

First-Principles Study of Electronic Structure of the Laves Phase ZrFe2

We perform the ab initio calculation for obtaining the density of states and magnetic properties of ZrFe2 Laves phase compound based on the method of augmented plane waves plus local orbital. The results indicate that the ferromagnetic state is more stable than the paramagnetic one, but with a slightly larger volume. The 3d−4d exchange interactions between Fe and Zr electrons lead to the antiparallel coupling for Fe 3d and Zr 4d states, which is responsible for the ferrimagnetic ordering of the compound. The resulting magnetic moment of about 1.98 μB for Fe is spatially localized near the Fe site, while around Zr a small but extended negative spin states causes a moment of about −0.44 μB. Moreover, the resulting magnetic moments with the generalized gradient approximation are more consistent with experimental values than that of the local-spin density approximation.

Electronic Structure and Magnetic Properties of SmCo7−xZrx

The electronic structure and magnetism of SmCo7−xZrx alloy are investigated using the spin-polarized MS-X. method. The results show that a few of electrons are transferred to the Sm(5d0) orbital due to orbital hybridization between Sm and Co atoms. The exchange interactions between 3d and 5d electrons are more important than the polarization effects of the conductive electrons, thus it is the main reason resulting in the long-range ferromagnetic order in SmCo7−xZrx. The Curie temperature of SmCo7−xZrx is generally lower than that of corresponding pure Co, which may be explained by the weaker average coupling strength between Co lattices due to some negative couplings mainly occurring of 2e site. The calculated results for the Sm5Co32Zr2 cluster may lead to a better understanding of why SmCo7−xZrx is stable phase. Since the spin-up DOS peak of d electrons at EF arises and the bonding of electrons at EF strengthens with increasing Zr concentration, which results in the internal energy of the system decrease, the stable ferromagnetic order forms in SmCo7−xZrx.

Electronic Structure and Magnetism in Sm(Co,Cu)7

The electronic density of states, spin-splittings and atomic magnetic moments of SmCo7−xCux are studied by means of the spin-polarized multi-scattering Xα method. The results show that a few of the electrons can transfer to the Sm 5d0 orbital due to orbital hybridization between Sm and Co. The exchange interactions between 3d and 5d electrons lead to the magnetic coupling between Sm and Co, and therefore result in the long-range ferromagnetic order in SmCo7−xCux. The Curie temperature of SmCo7−xCux is generally lower than that of the corresponding pure Co, which may be explained by the weaker average strength of coupling between Co lattices due to some negative exchange couplings mainly from the 2e site. The calculated results for the Sm5Co30Cu4 cluster may lead to a better understanding of why SmCo7−xCux is stable phase. Since the negative coupling of the 2e sites becomes small and the d bond at EF becomes stronger in contrast to SmCo7, which results in decrease of the free energy of the system, the stable ferromagnetic order forms in SmCo7−xCux.

Exchange Coupling and Stability of SmCo7?xHfx

Electronic structure of SmCo7−xHfx compound is calculated by using the multi-scattering Xα method. It is shown that a few of electrons can transfer to the Sm 5d orbital due to orbital hybridization between Sm and Co atoms. The 3d-5d coupling is stronger, which is the main reason to result in the long-range ferromagnetic order between Sm and Co atoms in SmCo7−xHfx. According to the Stoner criterion, the result of spin-unpolarized calculation for the Sm5Co32Hf2 cluster could lead to a better understanding of why the ferromagnetic SmCo7−xHfx is a stable phase. For the Sm5Co32Hf2 cluster the Fermi level is situated at the overall maximum of the density of states. Moreover the cluster wavefunctions at EF are antibonding and hence highly localized in real space, which would lead to a large value for the cluster Stoner integral. Thus a rationalization for the magnetic stability of SmCo7−xHfx has been obtained.