Van Vleck, J. (1932). "Theory of the Variations in Paramagnetic Anisotropy Among Different Salts of the Iron Group". Physical Review. 41 (2): 208–215. Bibcode:1932PhRv...41..208V. doi:10.1103/PhysRev.41.208.
Penney, William G.; Schlapp, Robert (1932). "The Influence of Crystalline Fields on the Susceptibilities of Salts of Paramagnetic Ions. I. The Rare Earths, Especially Pr and Nd". Physical Review. 41 (2): 194–207. Bibcode:1932PhRv...41..194P. doi:10.1103/PhysRev.41.194. ISSN0031-899X.
Schlapp, Robert; Penney, William G. (1932). "Influence of Crystalline Fields on the Susceptibilities of Salts of Paramagnetic Ions. II. The Iron Group, Especially Ni, Cr and Co". Physical Review. 42 (5): 666–686. Bibcode:1932PhRv...42..666S. doi:10.1103/PhysRev.42.666. ISSN0031-899X.\
Van Vleck, J. (1932). "Theory of the Variations in Paramagnetic Anisotropy Among Different Salts of the Iron Group". Physical Review. 41 (2): 208–215. Bibcode:1932PhRv...41..208V. doi:10.1103/PhysRev.41.208.
Penney, William G.; Schlapp, Robert (1932). "The Influence of Crystalline Fields on the Susceptibilities of Salts of Paramagnetic Ions. I. The Rare Earths, Especially Pr and Nd". Physical Review. 41 (2): 194–207. Bibcode:1932PhRv...41..194P. doi:10.1103/PhysRev.41.194. ISSN0031-899X.
Schlapp, Robert; Penney, William G. (1932). "Influence of Crystalline Fields on the Susceptibilities of Salts of Paramagnetic Ions. II. The Iron Group, Especially Ni, Cr and Co". Physical Review. 42 (5): 666–686. Bibcode:1932PhRv...42..666S. doi:10.1103/PhysRev.42.666. ISSN0031-899X.\
Penney, William G.; Schlapp, Robert (1932). "The Influence of Crystalline Fields on the Susceptibilities of Salts of Paramagnetic Ions. I. The Rare Earths, Especially Pr and Nd". Physical Review. 41 (2): 194–207. Bibcode:1932PhRv...41..194P. doi:10.1103/PhysRev.41.194. ISSN0031-899X.
Schlapp, Robert; Penney, William G. (1932). "Influence of Crystalline Fields on the Susceptibilities of Salts of Paramagnetic Ions. II. The Iron Group, Especially Ni, Cr and Co". Physical Review. 42 (5): 666–686. Bibcode:1932PhRv...42..666S. doi:10.1103/PhysRev.42.666. ISSN0031-899X.\