Magnetism and local order II: self-consistent cluster calculations

The effect of the local environment on the magnetic moment and its convergence to bulk value has been studied self-consistently by using a molecular-cluster model within the framework of spin-density-functional theory. We show that the magnetic moment of the central atom in clusters of 43 Ni atoms and 27 Fe atoms can reproduce the bulk values very well. The moments of atoms surrounding the central site increase as one approaches the surface-a consequence of decreasing coordination number. The defects such as vacancies and carbon and phosphorous impurities have a strong effect on the magnetic moment of the nearest host atom: The vacancies enhance the moments while the impurities quench them. The former is caused by a reduction in the coordination number, whereas the latter is caused by pd hybrids formed out of interacting impurity p and host d states. The effect of multiple defect complexes on the host magnetic properties has also been investigated, and the results are compared with available experimental data.