Anisotrope Hyperfeinwechselwirkungen in magnetischen Kobalt-Metalloidverbindungen

The NMR-spectra of Co in amorphous and crystalline magnetic CO$_{l-x}$ (P,B)$_{x}$ are influenced by anisotropic, magnetic hyperfine fields (HFF) and electric field gradients (EFG). A nuclear magnetic double resonance technique is introduced in order to measure the distribution of both fields and their correlation. Using this technique the full HFF- and EFG-tensors of Co in c-CO$_{2}$B were determined in full agreement with the data given by Kasaya et al. $^{28}$. The asymmetry of both tensors is large and nearly equal, the ratio of their maximum eigenvalues is similar to that known from hcp-Co. In c-Co$_{3}$ B only three eigenvalues of the two different Co-sites could be measured. The anisotropy of the HFF is larger than proposed in earlier studies on this material. The shape of the Co-spectra in a-Co$_{l-x}$ (P,B)$_{x}$ depends only on the HFF-distribution, the EFG being smaller by more than an order of magnitude. In contrast to the crystalline samples no correlation between HFF and EFG was found in the amorphous metals and the EFG-distributions do not depend on the metalloid atom. The EFG in Co containing many lattice defects has the same order of magnitude. The EFG in these amorphous metals thus seems to originate from topological rather than from chemical disorder