Atomic origin of magnetocrystalline anisotropy in Nd(2)Fe(14)B

The magnetic moment reversal at each of the two inequivalent Nd sites in a single crystal of ferromagnetic Nd(2)Fe(14)B is probed by dichroic resonant diffraction of circularly polarized x rays. The results, supported by theory, show that the c-axis intrinsic magnetic stability of this superior permanent magnetic material arises predominantly at one of the Nd sites (g). The other site (f) undermines magnetic stability by favoring a magnetic moment orientation in the basal plane.     

Magnetic properties of off-stoichiometric R2Co3Zn14 (R=Y,Gd) single crystals

Single crystal X-ray diffraction data indicate that the R₂Co₃Zn₁₄ (R=Gd, Y) phase crystallizes non-stoichiometrically with a mixed occupancy of Co/Zn atoms on the 12-coordinated transition metal site and one of the three zinc sites. The crystals are rhombohedral with R-3m space group. Magnetization measurements provide no evidence of localized 3d electron moment in Y₂Co_2.3Zn_14.7 which is non-magnetic down to 1.8 K. Thermodynamic and transport measurements on two Gd₂Co_3+xZn_14−x crystals reveal that the extra cobalt influences temperature below which the samples enter into an antiferromagnetic state: T_N=31.5(3) K for Gd₂Co₃Zn₁₄ and 28(1) K for Gd₂Co_4.2Zn_12.8. A lower magnetic ordering temperature of T_mag=6.0(2) K is common in both Gd samples.     

Quantum mechanical studies on model α‐pleated sheets

Pauling and Corey proposed a pleated‐sheet configuration, now called α‐sheet, as one of the protein secondary structures in addition to α‐helix and β‐sheet. Recently, it has been suggested that α‐sheet is a common feature of amyloidogenic intermediates. We have investigated the stability of antiparallel β‐sheet and two conformations of α‐sheet in solution phase using the density functional theoretical method. The peptides are modeled as two‐strand acetyl‐(Ala)₂‐N‐methylamine. Using stages of geometry optimization and single point energy calculation at B3LYP/cc‐pVTZ//B3LYP/6‐31G* level and including zero‐point energies, thermal, and entropic contribution, we have found that β‐sheet is the most stable conformation, while the α‐sheet proposed by Pauling and Corey has 13.6 kcal/mol higher free energy than the β‐sheet. The α‐sheet that resembles the structure observed in molecular dynamics simulations of amyloidogenic proteins at low pH becomes distorted after stages of geometry optimization in solution. Whether the α‐sheets with longer chains would be increasingly favorable in water relative to the increase in internal energy of the chain needs further investigation. Different from the quantum mechanics results, AMBER parm94 force field gives small difference in solution phase energy between α‐sheet and β‐sheet. The predicted amide I IR spectra of α‐sheet shows the main band at higher frequency than β‐sheet. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Effect of 3d doping on the electronic structure of BaFe2As2

The electronic structure of BaFe(2)As(2) doped with Co, Ni and Cu has been studied by a variety of experimental and theoretical methods, but a clear picture of the dopant 3d states has not yet emerged. Herein we provide experimental evidence of the distribution of Co, Ni and Cu 3d states in the valence band. We conclude that the Co and Ni 3d states provide additional free carriers to the Fermi level, while the Cu 3d states are found at the bottom of the valence band in a localized 3d(10) shell. These findings help shed light on why superconductivity can occur in BaFe(2)As(2) doped with Co and Ni but not Cu.