SPECTRAL DIFFUSION STUDIES OF THE Cr3+ ION USING ELECTRON SPIN ECHOES

Abstract

Spectral diffusion studies of the Cr³⁺ ion in the lattices of RbAl(SO₄)_2∙12H₂O (alum) and K₃Co(CN)₆ (cyanide) have been made, using electron spin-echo techniques. Below 4.2 °K, the nearly temperature-independent behavior suggests that echo attenuation is caused primarily by local field fluctuations due to spin–spin flips. In alum, the nearby nuclear magnetic moments of hydrogen determine the echo attenuation, which is essentially independent of the Cr³⁺ concentration below 6.7 × 10¹⁸ ions/cc. Conversely, in cyanide, the echo attenuation depends strongly on the Cr³⁺ concentration, which indicates that the diffusion is caused by other Cr³⁺ moments. However, the Cr³⁺ decay times were reduced by the addition of Fe³⁺ ions to the cyanide samples. The results follow a "nearly" Lorentzian diffusion law, as predicted theoretically by Klauder and Anderson (1962). Echo behavior indicates inhomogeneous resonance lines in alum at 1.7 × 10¹⁹ Cr³⁺ ions/cc and in cyanide between 1.5 × 10¹⁹ and 4.7 × 10¹⁸ Cr³⁺ ions/cc.