Anisotropic hyperfine interaction-induced spin relaxation in a low magnetic field

Spin relaxation caused by modulation of an anisotropic hyperfine interaction (HFI) in a low magnetic field has been correctly considered for a radical with one magnetic nucleus in a framework of Redfield relaxation theory. The analysis of the results obtained revealed that HFI-induced relaxation is very different in a low magnetic field from that in a high field; and that the use of traditional high-field expressions for calculation of T1 and T2 is not correct. It has been shown that taking correct account of the role of HFI-induced relaxation is crucial for the calculations of time-resolved CIDEP and the line width of EPR in a low magnetic field. In calculations of low-field CIDNP and MARY, taking correct account of the relaxation mainly influences the amplitude of the field dependence.