Ding-sheng Wang

Validity of the force theorem for magnetocrystalline anisotropy

Abstract The validity of the so-called force theorem is critical for the computational/theoretical determination of the magnetocrystalline anisotropy (MCA) in the framework of local density theory. This theorem states that the spin-orbit coupling induced MCA energy is given by the difference in the fully relativistic band energies between two magnetization directions calculated with the same self-consistent scalar-relativistic potential. We show that the charge- and spin-density variations caused by spin-orbit coupling vanish to first order in the spin-orbit coupling strength. By the stationary property of the total energy functional, we establish rigorously the validity of the force theorem for surface/interface MCA. We show that our arguments also apply to a variant of the MCA force theorem and discuss problems of applying the force theorem for MCA in bulk systems with cubic crystalline symmetry.

Calculations of stacking fault energy for fcc metals and their alloys based on an improved embedded-atom method

Abstract An accurate and simple model for calculating stacking fault energies has been developed based on our improved embedded-atom method. Using this model we have calculated stacking fault energies for some pure fcc metals and some fcc disordered solid solutions for NiCu, NiCo, NiAl alloys. The calculated results are in good agreement with the experimental ones.

Electronic structure and magnetic properties of δ-MnGa

Abstract The electronic structure and magnetic properties of δ-MnGa are studied by using the self-consistent linearized augmented plane-wave (LAPW) method. The analyses from the band structure, the density of states, total energy and the magnetic moments show that the ground states of the unstrained and strained δ-MnGa are in ferromagnetic phases, and the magnetic structures are affected significantly by strain.

Theoretical prediction of ferrimagnetism in face-centered cubic iron

Abstract The magnetic structure of fcc Fe has been investigated in a range of lattice constants from a = 3.50 to 3.75 A by the first-principles all-electron linearized augmented plane wave method in the local spin-density functional approximation. Besides the previously reported antiferromagnetic phase, one high-spin and two low-spin ferromagnetic phases, a ferrimagnetic phase is predicted to coexist in the range of a = 3.59 to 3.67 A.

Electronic structure of fcc iron in metastable magnetic phases

Abstract The electronic and magnetic structure of fcc Fe has been investigated for a range of lattice constants from a = 3.30 to 3.75 A by the first-principles all-electron linearized augmented planewave method in the local spin-density functional approximation. Electronic band structure, density of states, charge and spin densities of fcc Fe for all known possible magnetic phases of collinear spin configuration are presented and discussed. Besides the previously reported antiferromagnetic, high-spin and two low-spin ferromagnetic phases, a ferrimagnetic phase is predicated to co-exist in the range a = 3.59 – 3.67 A. The calculated moments of the two magnetic sublattices of fcc Fe with Cu lattice constant (a = 3.61 A) are 1.91 and −1.29μB. The total energy of the ferrimagnetic phase is as low as the antiferromagnetic phase which was believed to be the lowest in energy previously.

Self-consistent calculation of the multiphoton absorption coefficients of crystalline solids

Abstract The multiphoton absorption coefficients of typical crystalline solids are calculated by the first-principles all-electron self-consistent linearized augmented plane wave method in the local-density approximation and the high-order perturbation theory. The crystals studied include the group IV semiconductor Ge, the III–V compound GaAs, II–VI semiconductor CdTe and ionic crystals NaCl and KBr. Calculated 2-, 3-, 4-photon absorption coefficients are approximately in agreement with available experimental data in their orders of magnitude.

Orientation and structure dependence of interface magnetocrystalline anisotropy of Co/Cu overlayers and superlattices

The full potential linearized augmented plane wave method and atomic force approach are employed for the theoretical determination of interface magnetocrystalline anisotropy (MCA) for superlattice systems of Co/Cu in (001), (110), and (111) orientations, and overlayer systems of the monolayer Co on Cu (111) substrate adsorbed by different further coverage of Cu. It is found in superlattices that the interface MCA is sensitive to the geometry arising from different orientations. In good agreement with experiment, the interface MCA with Cu overlayers is found to peak at 1 monolayer of Cu‐coated Co/Cu(111) and then to decrease with further Cu deposition. In addition to the hybridization of electronic states at the Co/Cu interface, the interaction between the interface layers and the next‐to‐interface layers in superlattices and structure relaxation in overlayers may have a significant influence on the MCA of the Co layer.

First principles determination of magnetocrystalline anisotropy for surfaces and interfaces using a torque method (abstract)

Perpendicular magnetic alignment is vital for high density magneto‐optical recording materials. Despite the tremendous theoretical/computional advances made during the last few decades, the determination of magnetocrystalline anistropy (MCA) from first principles still remains a great challenge for complex systems. We will describe our recently proposed torque method for the first principles determination of MCA. In the usual first principles methods, one calculates the band energies associated with two magnetization directions and substracts one from the other. Within this approach, one has the difficulty of getting rid of the random fluctuations arising from the two different Fermi surfaces due to different magnetization directions. We show that to accurately determine the spin‐orbit induced uniaxial ansisotropy energy for surfaces/interfaces, calculation of the torque at a specific angle is sufficient and one avoids the complexities associated with two Fermi surfaces by employing the Feynman‐Hellman th...

A new embedded-atom potential for metals and its applications

Abstract Analytic expression for embedded-atom potentials is extended to varieties of cubic and hexagonal materials. These pair potentials are computationally simple and rather accurate. The basic equations are developed and applied to metals and diamond which exhibit different types of bonding. The expressions are used to calculate the vacancy formation energy for bcc Fe and stacking fault energies for several fcc metals. The results are in good agreement with the experimental findings.