Structural transformation of spin nanoclusters in low-dimensional anisotropic ferromagnets under applied magnetic field

Noncollinear discrete domain walls in the Heisenberg anisotropic ferromagnetic chain under applied magnetic field and their small excitation spectra are studied analytically and numerically in the framework of the Takeno– Homma equation. The intersecting frequency dependences of localized excitations and continuous spectrum oscillations and the removal of the degeneracy by the magnetic field are revealed. The variational approach is proposed to describe the domain walls and to investigate their stability. It is shown that the obtained analytical expressions fit very well the numerical solutions. The total energy of static discrete domain walls and the Peierls energy barrier between them are found explicitly. The stability diagram for noncollinear domain walls on the plane of parameters of the exchange and the magnetic field is calculated, and it looks like the alternating stripes structure of stability regions of the bond-centered and site-centered discrete domain walls. This diagram feature is explained by the oscillating dependence of the Peierls energy barrier on the exchange and the magnetic field parameters. (author)