In the framework of the theory of spin fluctuations, magnetic h-T diagrams of chiral helicoidal ferromagnets FexMn1-xSi with the Dzyaloshinskii-Moriya interaction are investigated. A specific analysis of the equations of magnetic state is carried out on the basis of a model of the electronic structure following from the LDA + U + SO DOS calculations in the virtual crystal approximation. It was shown that in the concentration range x <0.12, the Fermi level remains within the local minimum DOS. In this case, a helicoidal long-range order is realized, which undergoes a first-order transition induced by spin fluctuations, accompanied by the formation of intermediate skyrmion phases induced by an external magnetic field. With increasing x arising due to the chaotic distribution of the magnetic moments of manganese and iron over the nodes, the effects of concentration fluctuations suppress zero-point quantum spin fluctuations. In this case, the condition for the appearance of skyrmion phases is violated for x> 0.12, and the region of the helicoidal ferromagnetic order is preserved up to concentrations xc = 0.20. In the interval 0.10 <x <0.20, the transition induced by fluctuations to the paramagnetic state is accompanied by the disappearance of local magnetization and the formation of a paramagnetic state with dynamic spin correlations.
Persistence of Ising-like easy-axis spin correlations in the paramagnetic state of the spin-1 chain compound
NiTe2O5
