Spin-Spin Absorption in Manganous Chloride Tetrahydrate

Measurements on spin-spin absorption have been made on the antiferromagnetic substance, MnCl₂·{}4H₂O, at temperatures from 1.3 to 4.2^∘{}K and at frequencies 1, 2, and 4 Mc/sec. The absorption shows a sharp peak at about 2.3^∘{}K and is proportional to the square of the frequency. At the highest temperatures an attempt has been made to compare the results with theory. The agreement is reasonable considering the extremely complicated situation where Stark splitting and dipolar, exchange and hyperfine coupling all are important. It is pointed out that an extension of this type of measurement to more simply behaved salts would be of considerable interest.