PHYSICAL ORIGIN OF MULTIPLE THREE AND FOUR SPIN (OR ATOMS) EXCHANGE IN QUANTUM SOLIDS WITH SOME CONSEQUENCES J. M. Delrieu, M. Roger et J. H. HetheringtonJ. Phys. Colloques, 41 C7 (1980) C7-231-C7-239DOI: https://doi.org/10.1051/jphyscol:1980737
