Anomalous hydrostatic pressure dependence of the Curie temperature of the kondo-lattice compound YbNiSn to 38GPa

The dependence of the Curie temperature T-0 of ferromagnetic YbNiSn on hydrostatic pressure to 38 GPa has been determined in an ac susceptibility measurement in a diamond-anvil cell loaded with dense helium as a pressure medium. The Curie temperature T(0)similar or equal to 5.5 K initially increases with applied pressure at the rate +1.7 K/GPa, passing through a maximum value T(0)(max)similar or equal to 7.7 K at similar to 2 GPa. No transition was detected above 2 K for 9.4 GPa<P<38 GPa. The present results are discussed within the framework of a phase diagram proposed by Doniach for Kondo-lattice systems. The observed asymmetry in T-0(P) about P-m=P(T-0(max)), which is opposite to that found in Ce compounds, can be readily understood in Doniach's model if the Kondo temperature of YbNiSn decreases under pressure.