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Angular-modulation-induced reverse-phase first-derivative field-swept EPR spectra

Journal of Magnetic Resonance (1969)
Publication Date
DOI: 10.1016/0022-2364(84)90122-7


Abstract Field-swept EPR is commonly observed as a first-derivative spectrum resulting from use of a high-frequency modulation field, parallel to the sweeping do field. In single-crystal studies it is sometimes convenient to rotate the do magnetic field ( B) thus creating a misalignment with respect to the modulation field ( B m), and this leads to an angular-modulation effect in addition to the usual field modulation, since the resultant magnetic field at the sample changes in direction about the applied do magnetic field. If the transition fields vary rapidly enough with crystal orientation and/or the angle between the modulation and dc fields is great enough, the effects of angular modulation can dominate the first-derivative spectral response. Angular-modulation effects manifest themselves first, in the occurrence of finite signal intensities when B is perpendicular to B m and, second, when neither parallel nor perpendicular to B m by causing some first-derivative lines to disappear and then reappear with their phase reversed as B is rotated further away from B m. Such reverse-phase effects in EPR arise as a natural consequence of the presence of a component of the modulation field normal to the do magnetic field. In this paper, angular-modulation effects are reported for Cr 3+ transitions in ruby single crystals along with computer simulations of the spectra based on appropriate combinations of field- and angular-modulation contributions.

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