On the stability of the ferromagnetic state in the Kondo-lattice compound YbNiSn under high pressure

The effect of pressure on the electrical resistance R(T, p) (where p less than or equal to 13 GPa and 1.8 K less than or equal to T < 300 K) and the lattice parameters (p less than or equal to 26.4 GPa at T = 300 K) of the ferromagnetic Kondo-lattice compound YbNiSn (T-C = 5.5 K at ambient pressure) has been investigated using the diamond anvil cell technique. The x-ray diffraction data show a smooth decrease of the lattice parameters upon increasing pressure, indicating no structural phase transition up to 26.4 GPa. R(T, p) measurements show for 0 less than or equal to p less than or equal to 9 GPa the same pressure dependence of T-C as obtained from very recent high-pressure ac susceptibility (chi ac(p)) measurements. However, unlike for the chi ac(p) measurements, where the ferromagnetic signal is lost for pressures p greater than or equal to 9.4 GPa, we find an almost pressure-independent value of T-C in the pressure range 6 less than or equal to p less than or equal to 13 GPa, i.e. no indication of a discontinuous change of the type of magnetic order is observed at p = 9.4 GPa. We further discuss the correlation between the pressure dependence of T-C and that of the characteristic temperature of crystal-electric-field effects T-CEF*.