Competing Anisotropies in the Ferromagnetic Kondo-Lattice Compound YbNiSn: Observation of a Complex Magnetic Ground State under High Pressure

The ${}^{170}\mathrm{Yb}$ high pressure Mössbauer-effect technique has been used to investigate on a microscopic level the ground state properties of the ferromagnetic (FM) Kondo-lattice compound YbNiSn. Unlike general expectations, we find for $0\le p\le 3\mathrm{GPa}$ a stable moment behavior while $T_C$ is enhanced to its maximum value. For $p>\mathrm{}3\mathrm{}\mathrm{GPa}$ we observe a gradual change of the FM state to a complex magnetic ground state. This is suggested to be due to a volume dependent competition between the anisotropy of the magnetic exchange interaction and the crystal electric field anisotropy.