Sihuai Chen

Effects of buffer layer and substrate temperature on the surface morphology, the domain structure and magnetic properties of c-axis-oriented Nd2Fe14B films

Anisotropic Nd-Fe-B thin films with c-axis texture are fabricated by dc magnetron sputtering on heated Si substrate. The influence of Ti or Mo buffer layer thickness and substrate temperature on the surface morphology, the domain structure and the magnetic properties are investigated and compared for the Nd-Fe-B films. It is found that the morphology of the surface strongly depends on the thickness of the buffer layer. A rough surface is observed if there is no buffer layer between the substrate and Nd-Fe-B layer or the buffer layer is too thick. Mo shows to be the better candidate for the buffer layer for its perfect lattice match with the Nd-Fe-B layer. The best values for the maximum energy products are 11.9 and 14.8 MGOe for the Nd-Fe-B films with Ti and Mo buffer layers, respectively. (c) 2005 American Institute of Physics.

Structural, magnetic and magnetostrictive properties of Tb0.2Pr0.8(Fe0.4−xCo0.6+x)1.93 alloys

Structural, magnetic and magnetostrictive properties of Tb0.2Pr0.8(Fe0.4-xCo0.6+x)(1.93) (0 <= x <= 0.2) alloys have been investigated by means of x-ray diffraction, ac initial susceptibility, a superconducting quantum interference device magnetometer and a standard strain gauge technique. A single (Tb, Pr)(Fe, Co)(2) Laves phase with a cubic MgCu2-type structure is formed when 0.05 <= x <= 0.2. Increasing the Co content in the Tb0.2Pr0.8(Fe0.4-xCo0.6+x)(1.93) alloys reduces the magnetocrystalline anisotropy constant K-1 and improves the magnetostrictive properties at relatively low magnetic fields at room temperature. The Tb0.2Pr0.8(Fe0.35Co0.65)(1.93) alloy with a single Laves phase has a spontaneous magnetostriction lambda(111) as high as 1900 ppm, a large magnetostriction lambda(a) (=lambda(parallel to) - lambda(perpendicular to)) at a relatively low magnetic field and a large lambda(a)/K-1, and may make it a promising magnetostrictive material.

Structure and magnetic properties of high-energy product Nd-Fe-B/Nd-O thin films

Nd2Fe14B/Nd-O thin films with high- energy product (BH) (max) = 33.9 MGOe are fabricated by a one-step sputtering process, i.e. dc magnetron sputtering on a Si substrate heated at 600-650 degrees C, without a post-deposition annealing process. The highly anisotropic Nd-Fe-B/Nd-O thin film with high-energy product is realized immediately after the deposition, owing to the anisotropic growth of both the Nd-O and the Nd2Fe14B phases. The coexistence of the nanoscale Nd2Fe14B and Nd-oxide phases in the thin films is confirmed by means of x-ray diffraction, high-resolution transmission electron microscopy (HRTEM) and energy-filtered transmission electron microscopy. The boundaries between the buffer layer and the Nd-Fe-B layers and the different phases are investigated by HRTEM.

Synthesis, structures and magnetic properties of linear {CoII2LnIII2} coordination clusters

Three linear heterometallic CoII2LnIII2 (Ln = Dy (1), Gd (2), Y (3)) coordination clusters have been synthesized under solvothermal conditions. Single-crystal X-ray diffraction studies revealed that all three compounds are isostructural and crystallize in the monoclinic space group P21/c with Z = 2. The dc magnetic susceptibilities for all three compounds have been measured and the magnetic exchange couplings (for 2) and magnetic anisotropy for CoII ions (for 2 and 3) have been calculated and discussed. Furthermore, the ac magnetic susceptibility measurements have been performed and show that CoII2DyIII2 compounds 1 display single-molecule magnetic (SMM) behavior.

Targeted replacement: systematic studies of dodecanuclear {MIII6LnIII6} coordination clusters (M = Cr, Co; Ln = Dy, Y)

Three dodecanuclear 3d-4f coordination clusters, [CrIII6LnIII6(μ3-OH)8(tbdea)6(C6H5COO)16]·2H2O (Ln = Dy (1), Y (2)) and [CoIII6DyIII6(μ3-OH)8(nbdea)6(m-CH3C6H4COO)16]·2H2O·2CH3CN (3), have been synthesized under solvothermal conditions and characterized. Single-crystal X-ray diffraction analysis revealed that all three compounds possess an analogous {MIII6LnIII6} core (M = Cr, Co; Ln = Dy, Y) and dc magnetic susceptibility studies indicated that the magnetic exchange couplings between DyIII ions are dominant antiferromagnetic, while the CrIII-DyIII interactions are weakly ferromagnetic. Furthermore, the ac magnetic susceptibility measurements showed that both CrIII6DyIII6 compound 1 and CoIIi6DyIII6 compound 3 containing highly anisotropic DyIII ions displayed single-molecule magnetic (SMM) behavior with the energy barrier Ueff increasing from 12.8 K (for 1) to 20.8 K (for 3), indicating that weak 3d-4f exchange couplings enhance the QTM and reduce the energy barrier.