1. H. B. G. Casimir and F. K. du Pré, Commun. Kamerlingh Onnes Lab. Leiden Suppl. No. 85a
2. Note on the thermodynamic interpretation of paramagnetic relaxation phenomena
3. W. J. de Haas and F. K. du Pré, Commun. Kamerlingh Onnes Lab. Leiden No. 253a
4. Paramagnetic relaxation in iron ammonium alum at low temperatures