SPIN-SPIN INTERACTION CONSTANTS FROM HYPERFINE STRUCTURE OF PAIRS OF COUPLED IONS

The hyperfine structure of pairs of paramagnetic ions with identical nuclear spins and a spin-spin interaction effectively of the form K0S1•S2+KzS1zS2z is discussed. The structure of the spectra depends on the ratio p=K0A, and a general discussion of the key features of the spectra is given for p in the range zero to infinity. The technique by which the spin-spin interactions may be extracted from the spectra is demonstrated by four examples which correspond to p values of 2, 5.7, 11, and 48. In all cases Kz is sufficiently large that a major part of the hyperfine structure of the pairs is clear of the spectrum of the isolated ions. For the nearest-neighbor axial pairs of Pr3+ in La2 (C2H5SO4)6•9H2O, K0=+0.467 cm-1 and Kz=-0.474 cm-1; for Pr3+ in LaCl3, the nearest-neighbor axial pairs have K0=2.44 cm-1 and Kz=1.79 cm-1, where the z axis here and below is the interionic axis and the trigonal axis of the crystal. The other two examples are provided by Co2+ in the nearest-neighbor X sites of La2Mg3(NO3)12•24H2O; one for the magnetic field along the interionic axis, and the other for the magnetic field perpendicular to this axis. One finds K0=+0.105 cm-1, and Kz=-0.170 cm-1. © 1969 The American Physical Society.