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The sample of compound NdNi 2 Ge 2 is prepared by arc melting. The crystal structure is analyzed using powder X-ray diffraction and refined with Rietveld is method. It is shown that NdNi 2 Ge 2 intermetallic compound crystallizes into a tetragonal structure with space group of I/4mmm and its lattice constant is a =4.120(1), c =9.835(0), Z =2. Nd atoms occupy 2a positions, Ni atoms 4d positions and Ge atom 4e positions. NdNi 2 Ge 2 intermetallic compound has a Curie-Weiss constant of 25.8 and Curie-Weiss temperature of 6.24 K. The effective magnetic moment is 3.69 μ B , which is very close to that of Nd 3+ . It implies that the magnetic moment originates mainly from Nd 3+ ion. The resistivity varies from 0.3 Ω ·μm—1.1 Ω ·μm. Fitting results show that this intermetallic compound is semimetal.

The rare earth-iron based 3:29 and 1:12 type intermetallic compounds have the potential application as novel permanent magnetic materials due to their hard magnetic properties at room temperature. The study on the magnetism of these intermetallic compounds is beneficial for the research and development of their applications as novel rare earth permanent magnetic materials. In this study, the traditional magnetic valence model has been developed for extending its application from the strong magnetic alloys and intermetallic compounds to the weak magnetic systems with ferrimagnetic order. The developed magnetic valence model has been used to investigate the magnetisms of RFe 12- x M x , R 3 Fe 29- x M x and R 2 Fe 17- x M x (R=rare earth; M=the doped metals such as Ti, Mo, V, etc) and their carbonates and nitrides. The theoretical calculations agree with the experiments well. The study shows that the magnetic moments of these kinds of rare earth iron based intermetallic compounds are related to the magnetisms of the rare earths in these intermetallic compounds. The weak magnetism in these intermetallics originates from the existence of some ferrimagnetic order pairs in the unit cell. The nitrogenation and carbonation process might induce the ferrimagnetic order pairs transiting to the ferromagnetic order pairs, and increase their moments. The contributions to the magnetic moments of the electrons in conducting band are related to the polarization of heavy rare earth and the capture abilities of carbon and nitrogen atoms to electrons. The developed magnetic valence model can predict the magnetic moments as long as the structural formula is known.

The typical magnetic domains of Sm(CobalFe0.25Cu0.07Zr0.02)7.4 magnets quenched through various heat-treatment steps have been revealed by using magnetic force microscopy (MFM). For the specimens in which the nominal c-axis is perpendicular to the imaging plane, the domain configurations change from plate-like for the as-sintered magnet to corrugation and spike-like for the homogenized one, and then to a coarse and finally to a finer domain structure when isothermally aged at 830°C and then annealed at 400°C. However, only plate-like domains can be detected on the surfaces with the nominal c-axis parallel to the imaging plane. The finer domain (so-called interaction domain) is a characteristic magnetic domain pattern of the Sm–Co 2:17-type magnets with high coercivities. Domain walls in a zigzag shape are revealed by means of MFM in final bulk Sm–Co 2:17-type sintered magnets.

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 of SmCo7−xTix alloy has been studied by means of the spin-polarized MS-Xα method. It is shown that a few of electrons are transferred to Sm(5d) orbital due to orbital hybridization between Sm and Co atoms. The exchange interaction between 5d-3d electrons is stronger, which is the main reason resulting in the long-range ferromagnetic order between Co and Sm atoms. The Curie temperature of SmCo7−xTix is generally lower than that of pure Co metal, which may be explained by the weaker average of coupling strength between Co sites due to some negative exchange couplings occurring mainly at 2e site. The calculated results for the Sm5Co28Ti6 cluster may lead to a better understanding of why SmCo7−xTix is stable phase. Since the negative interaction of 2e sites weakens and the bonding at EF strengthens with increasing Ti concentration, which result in the decrease in the free energy of the alloy, the stable ferromagnetic order forms inside SmCo7−xTix. Considering the localization of 4f states and 5d moment arising from the orbital hybridization, the calculated moment is 9.47 μB per formula unit that is in agreement with experiments.

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.

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.

The magnetic microstructures of two Dy–Al substituted sintered Nd–Fe–B magnets with the different nominal compositions of Nd12.2Dy0.6Fe80.4Al0.7B6 (at.%) (composition-A, C-A) and Nd13.7Dy0.6Fe78.8Al0.7B6.2(at.%) (composition-B, C-B) prepared by strip casting technique have been revealed by using a magnetic force microscope. The magnetic properties of sintered C-B magnets are worse than that of C-A sintered magnets. In particular, the value of density products (BH)max for sintered C-A magnets is about 32% higher than that of C-B magnets, which is reflected by their quite different magnetic microstructures. We believe that for the C-B samples, the inappropriate composition and thus the redundant Nd2Fe17(B) phase of the casting strips make its final magnetic microstructures worse than the C-A, and then deteriorates the performance of the C-B magnets.

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.

The magnetisms of RCo5 (R = rare earth) intermetallics are systematically studied with the empirical electron theory of solids and molecules (EET). The theoretical moments and Curie temperatures agree well with experimental ones. The calculated results show strong correlations between the valence electronic structure and the magnetic properties in RCo5 intermetallic compounds. The moments of RCo5 intermetallics originate mainly from the 3d electrons of Co atoms and 4f electrons of rare earth, and the s electrons also affect the magnetic moments by the hybridization of d and s electrons. It is found that moment of Co atom at 2c site is higher than that at 3g site due to the fact that the bonding effect between R and Co is associated with an electron transformation from 3d electrons into covalence electrons. In the heavy rare-earth-based RCo5 intermetallics, the contribution to magnetic moment originates from the 3d and 4f electrons. The covalence electrons and lattice electrons also affect the Curie temperature, which is proportional to the average moment along the various bonds.

Rare earth element is one kind of strategic materials. Some rare earth elements have been industrialized. They play major roles in permanent magnetism material, lightening, catalysis and hydrogen storage material. In order to understand the rare earth elements more, it is necessary to study the structures of the valence electrons and atoms of them. The valence electron structures and properties of yttrium, scandium and lanthanum group rare earth elements are studied with the empirical electron theory (EET). Based on the valence electron parameters, the melting points and cohesive energies of these rare earth elements are calculated. The calculations accord with those of the measurements. According to the analyses of EET, the structures and the physical properties of rare earth elements depend on the electron emission or transformation between the lattice-electrons and coherent electrons in outer orbital. It is exhibited that the melting point tends to increase with the lattice electron-covalent electron transformation, however, the valence status of rare earth element affects significantly the electron distribution and property. The covalent electron hoppings occur at divalent europium, ytterbium and samarium, and their melting points are related to the electron transformation covalence-electrons. It is different from the others with trivalent status. The theoretical analysis reveals that the cohesive energy is related to the 4f electrons. The contribution to cohesive energy increases with the number of 4f electrons increasing, which may be due to the shrinking effect of the atomic radius for the lanthanum group. The study implies that the characteriscs of rare earth element are due to the relation between their melt pointing and conhesive energy and electronic structure.

The valence electron structure and magnetic properties of Nd2Fe14B intermetallics have been investigated using empirical electronic theory of solids and molecules. The calculations fit the experimental data well. It reveals that the magnetic properties of Nd2Fe14B are proportion to the 3d electrons of Fe atoms. The moments increase from the Fe at 4c site to the Fe at 16k2 site, which is due to the changes between the valence electrons, dumb pair electrons and 3d magnetic electrons. According to the calculation, 78% of dumb pair electrons and 18% of valence electrons in d orbit change to magnetic electrons, this causes the increase of moments from the Fe at 4c site to the Fe at 16k2 site. Both Curie temperature and moments are proportion to the coordination numbers of the Fe atom, however, the Curie temperature decrease with the weighted equal bond numbers Iσ. The effect on Curie temperature of non-magnetic elements Nd and B is derived from the change of the Fe—B and Fe—Nd bond distances.

The effects of exchange-coupling interactions between grains on the effective anisotropy and the variation in Nd2Fe14B/α-Fe nanocomposite permanent materials were investigated. The calculatied results showed that due to the exchange-coupling interactions, the effective anisotropy Keffof the nanocomposite decreases with the decrease of grain size and the increase of magnetically soft phase component. When the average grain size decreases to 4nm, Keff decreases to about 1/3—1/4 of the value of the ordinary anisotropy constant. This variation character is basically similar to that of the coercivity. The decrease of coercivity for the nanocomposite permanent materials is mainly due to the decrease of the effective anisotropy.