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What is superhyperfine structure in electron-spin resonance?

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magnetic resonance Figure 1: Precession of a magnetic dipole moment μ in the presence of a constant field H and a rotating field H′ (see text)

In electron-spin resonance (ESR), superhyperfine structure refers to the further splitting of hyperfine spectral lines caused by the interaction of electronic magnetization with multiple nuclei.1

While hyperfine structure arises from the interaction between electronic magnetization and a single nucleus, superhyperfine structure occurs when the electronic magnetization is spread over more than one atom. In such cases, the electrons interact with the nuclear moments of several neighboring atoms, and the hyperfine coupling is replaced by the sum of the couplings with all these nuclei. Each individual hyperfine line is then split further by these additional interactions.1

The observation of superhyperfine structure is significant because it provides a detailed mapping of electronic magnetization and serves as conclusive evidence of covalent bonding between a magnetic center and its neighboring ions. It is a valuable tool for testing the accuracy of models used to describe defects, such as vacancies at lattice sites or impurity centers in crystals.1