Was he Ernst (Nobel prize winner for NMR spectroscopy development) or early physicists, Bruker or Varian or some Russians? I just check your erudition (later I give you the reference).
It were Russians in 1958 (!!!!) from my home NMR group, department of physics, Saint Petersburg State University (former Leningrad University, USSR)! I am proud I have learned from, known, seen, talked to the two of them :)!! I write the historical reference in Russian and English below. I think there is an English translation of this journal.
Морозов А. А., Мельников А. В., Скрипов Ф. И., Методика свободной ядерной индукции в слабых магнитных полях в применении к некоторым задачам радиоспектроскопии высокой разрешающей силы, Известия АН СССР. 1958, Т. 22, № 9, С 1141-1144 (Russian language reference)
Morozov A. A., Melnikov A. V., Skripov F. I., Application of free nuclear induction technique in low magnetic fields to some problems of high resolution radio spectroscopy, Izvestiya USSR Academy of Sciences. 1958. Vol. 22, № 9, pp. 1141-1144 (in russian)