Spin-1 Blume–Capel model in a transverse crystal field: An improved variational approach

摘要: Abstract We examine the phase diagram of spin-1 Blume–Capel model in a transverse crystal field. Using an improved pair approximation within framework Bogoliubov variational approach for free energy, we go beyond simple mean-field (MFA) and effective field theory (EFT) at investigating this model. The present results may clarify important points with respect to multicritical phenomena diagram, which are not yet fully resolved, since MFA EFT yield conflicting results. Phase diagrams one, two three dimensions investigated, compared previous ones obtained by employing EFT. show how nature transition changes as both longitudinal fields varied. In addition, Ising is limiting case zero field, its also analysed carefully. analytical expressions critical equation finite well absolute temperatures. By means Landau expansion locate tricritical besides ones. Remarkably, quantum found dimensions. study behaviour thermodynamic quantities, namely magnetisation quadrupole moment, turn out be define order transitions.