First-order phase transition induced by quantum fluctuations in Heisenberg helimagnets

Abstract
The ground-state energy of a spin-density wave of wave vector Q in a Heisenberg ferromagnet with competing interactions is calculated for small Q as EG (Q)=EG (0)+A1Q2 +A2Q4+ . . . . The coefficients A1 and A2 are calculated exactly at zero temperature in the limit as the ferromagnet to helix transition is approached. For some ranges of parameters we find that quantum zero point motion causes A2 to become negative thus leading to a first-order transition not present in the classical system.

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