Magnetic anisotropy of antiferromagnet (CH3)(4)NMnCl3

The parameters of the electron paramagnetic resonance (EPR) spectra of S io n pairs in diamagnetic crystals are analyzed. A relation between the spin H amiltonian constants is established for solitary ions and pairs for (CH3)(4 )NCdCl3:Mn2+ crystals. In contrast to solitary ions, an additional contribu tion (which is a linear function of the exchange field) to the "single-ion" spin Hamiltonian constants appears in the case of pairs. It is shown that anisotropic exchange mechanisms do not play a significant part in the forma tion of the axial constant of the spin Hamiltonian for this crystal. Some a spects of the method of studying "single-ion" anisotropy predicted by the t wo-ion model are developed with the help of an isostructural diamagnetic an alog with impurity concentration of the paramagnetic ions of a magnetically concentrated substance sufficiently high for observing the EPR spectrum of the pairs. It is found that the microscopic quantities determined partiall y from the EPR spectra for pairs and solitary Mn2+ ions in (CH3)(4)NCdCl3 a re in accord with the experimental value of the effective field for the (CH 3)(4)NMnCl3 crystal anisotropy which can be described primarily by the dipo le and "single-ion" mechanisms of the exchange origin. (C) 2000 MAIK "Nauka /Interperiodica".