Ground-state energy of biquadratic spin systems (S=3/2) in the (1/z)1-approximation

Corrections to the molecular-field ground- state energies of the Heisenberg model with isotropic biquadrati c interactions (spin S = 3= 2) are calculated in the ( 1= z ) 1 -approximation using the diagrammatic technique based on the Wick reduction theorem (z is the numb er of spins interacting with any given spin) . The present results for the antiferri- and antiferromagnetic phases complete the previously obtained data for the antiquadrupolar, ferriand ferromagnetic phases. From among the boundaries between different ground states only that b etw een the antiferri- and antiferromagnetic phases is shifted with respect to its molecular-field value