J. E. Lowther

Ferromagnetism in IV main group element (C) and transition metal (Mn) doped MgO: A density functional perspective

The formation of magnetic moment due to the dopants with p-orbital (d-orbital) is named d0 (d −) magnetism, where the ion without (with) partially filled d states is found to be responsible for the observed magnetic properties. To study the origin of magnetism at a fundamental electronic level in such materials, as a representative case, we theoretically investigate ferromagnetism in MgO doped with transition metal (Mn) and non-metal (C). The generalized gradient approximation based first-principles calculations are used to investigate substitutional doping of metal (Mn) and non-metal (C), both with and without the presence of neighboring oxygen vacancy sites. Furthermore, the case of co-doping of (Mn, C) in MgO system is also investigated. It is observed that the oxygen vacancies do not play a role in tuning the ferromagnetism in presence of Mn dopants, but have a significant influence on total magnetism of the C doped system. In fact, we find that in MgO the d0 magnetism through C doping is curtailed by...

The Role Played by Computation in Understanding Hard Materials

In the last decade, computation has played a valuable role in the understanding of materials. Hard materials, in particular, are only part of the application. Although materials involving B, C, N or O remain the most valued atomic component of hard materials, with diamond retaining its distinct superiority as the hardest, other materials involving a wide variety of metals are proving important. In the present work the importance of both ab-initio approaches and molecular dynamics aspects will be discussed with application to quite different systems. On one hand, ab-initio methods are applied to lightweight systems and advanced nitrides. Following, the use of molecular dynamics will be considered with application to strong metals that are used for high temperature applications.

3.02 – From Diamond to Superhard Borides and Oxides

In the last decade, major advances in technology have helped the development of new materials with superhard properties. The synthesis of many of these materials is either consistent with theory or computational prediction. This chapter considers the impact of ab initio computation on the physical insight into the origin of superhardness in such materials. Materials ranging from diamond-like materials through to borides and oxides are examined.

Monte Carlo Calculations on a Lattice with Random Spin Interactions

A Monte Carlo procedure is introduced in which spin-flip dynamics are applied to a system that is characterized through random radial dependence of the exchange interaction. Application is made to a dilute system such as P in Si, where a topological distribution of spin orientation affects the measured magnetic susceptibility. Although a transition temperature is not clearly defined, a Curie-Weiss description is possible, the nature of which can still characterize the concentration of spins in the material. The spin dynamics does not directly reveal evidence of spin clustering and is not a valid approach below the transition temperature where quantum molecular effects dominate.