Field Behavior of Spin Models with Competing Interactions
Our interest in the study of spin hamiltonians with competing interactions has been stimulated by recent measurements for the field-temperature phase diagram of compounds which exhibit modulated phases1,2. In the first part of this talk we report mean-field calculations3 for the global T-p-H phase diagram of the ANNNI model (where p=-J2/J1 gives the strength of the axially competing interactions). At high temperatures we obtained several analytic results, but at low temperatures the modulated phases in a field were studied numerically. The analysis in the neighborhood of the critical surface was also supplemented4 by an ε-expansion renormalization-group treatment which will be reported in part II. We finally talk about an XY spin hamiltonian with competing interactions5 which is suitable for explaining the Lifshitz point in MnP.
KeywordsSpin Field Tricritical Point Multicritical Point Lifshitz Point High Harmonic Component
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