"Paramagnetic relaxation of liquid solutions for parallel fields": Zavoisky's foundational papers of Electron Paramagnetic Resonance
The article "The paramagnetic absorption of a solution in parallel fields" appeared in English (Journal of Physics, 1944, XIII:6, 377-380) and in Russian ("Парамагнитная абсорбция в растворах при параллельных полях", Журнал эксперимент. и теоретич. физики., 1945, 15:6, 253-257) and descibed the parallel-field EPR studies of MnSO4 solutions.
This paper was followed by perpendicular-field studies published on a subsequent issue of the same journal and can be found here.
Again, I would like to thank Mr. Igor I. Silkin from the Evgeni Zavoisky Museum for providing copies of those articles.