Field and anisotropy effects in spin glasses. I. The collinear case

Abstract

A theoretical analysis is given for the phase structure of a vector spin-glass model in the presence of local uniaxial anisotropy and/or coaxial external magnetic fields and/or spontaneous mean ferromagnetism. Replica analysis is used, including generalisations of Almeida-Thouless stability analysis and of Parisi treatment of replica-symmetry breaking. Phase transition points, lines and surfaces are found, as also irreversibility crossovers. Spin-glass phases include longitudinal, transverse and mixed; ferromagnetic include collinear and randomly canted (ferromagnet plus transverse spin glass). All spin-glass-type phases are accompanied by ergodicity-breaking of the corresponding symmetry while transverse ordering in a field is also accompanied by weak longitudinal irreversibility, followed by crossover to stronger irreversibility at a lower temperature.