Universality of magnetic susceptibility in the conical state of the kagome ferromagnet Fe3Sn2

We report universal behavior of the differential magnetic susceptibility (DMS) in the conical phase that mediates the spin-reorientation (SR) transition of the kagome ferromagnet Fe3Sn2. Within the SR temperature range, the DMS isotherms exhibit extremely narrow crossing regions, forming isosbestic points. Using an isosbestic-invariance analysis, we show that the isotherms collapse onto a single temperature-independent curve, revealing quadratic-in-temperature corrections to the susceptibility. Complementary field-dependent magnetic-force-microscopy measurements uncover the evolution of spin textures from stripe-like domains at low fields to isolated bubble-like domains near the isosbestic field (∼0.6 T), a behavior not previously reported in bulk Fe3Sn2 within the conical state. These findings point to a universal mechanism for the emergence of complex magnetic textures near isosbestic points, driven by the competition between magnetocrystalline anisotropy, dipolar interactions, and external magnetic field.