Thermodynamic theory of orientational phase transition in an inhomogeneously stressed easy plane weak ferromagnet

In the basal plane of a light-density iron borate single crystal, a spatially inhomogeneous magnetic anisotropy was indexed using nonsymmetric mechanical stresses. The temperature dependence of the vanishing field and the field dependences of the spatial period of the system of bands in the image of an inhomogeneously stressed crystal, as well as the dependence of the range of existence fields of the modulated phase of inhomogeneously stressed FeBO3 on temperature, are studied. The results obtained are discussed within phenomenological theory of magnetic phase transformations. It is shown that the applied theoretical model makes it possible to consistently describe the entire set of experimental results obtained in the study of the noncollinear magnetic phase of inhomogeneously strained FeBO3.