Antiferromagnetic Resonance in Sodium Clusters in Sodalite

Sodium clusters arrayed in aluminosilicate sodalite are known to show antiferromagnetism below the Neel temperature T N of 48 K. We have performed electron spin resonance (ESR) measurements on a powder specimen of this material at an X-band microwave frequency (9.7 GHz) with temperature varying between 4 and 300 K. The ESR spectra show asymmetric broadening below T N , which can be regarded as a powder pattern of the antiferromagnetic resonance (AFMR) signal. From the analysis of the AFMR fields at low temperatures using the exchange-coupling constants evaluated from the magnetic susceptibility, the anisotropy field is estimated to be significantly small at about 1–2 Oe. These results indicate that this material is an ideal Heisenberg antiferromagnet resulting from the character of s-electrons in zeolite cages with a cubic arrangement.