Mossbauer spectroscopy magnetic perturbations

One less-well-known technique, which has many experimental aspects in common with Mossbauer spectroscopy, deserves special attention at this point, since it gives valuable information about the electric-field gradients and the magnetic hyperfine interactions of radioactive nuclei in solids at ambient conditions and under pressure. In this technique, two y-rays with different energies from two different transitions of an individual nucleus in a radioactive-decay cascade are recorded consecutively. The spatial and temporal perturbation of the emission probability by the hyperfine fields is registered in the corresponding perturbed angular correlation (PAC) spectra. 

B. SURFACE HYPERFINE FIELD. The demagnetizing field and the Lorentz field are not defined for the atoms at the surface. Calculations of the magnetic dipole fields at atoms near the surface in fine particles and thin films of a-Fe show that only the first surface layer is perturbed, with variations of the order of lOkOe depending on the position at the surface. Studies of thin and ultrathin metal films by Mossbauer spectroscopy (see, e.g.. Refs. 31, 224, 238, and 239) show that one or two atomic layers are perturbed, as for the magnetization (see Section B.3). The surface hyperfine field may be larger or smaller than in the bulk at... 

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