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

The dependence of the Curie temperature ${\mathit{T}}_{\mathit{o}}$ 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 ${\mathit{T}}_{\mathit{o}}$(0)≃5.5 K initially increases with applied pressure at the rate +1.7 K/GPa, passing through a maximum value ${\mathit{T}}_{\mathit{o}}^{\max }$≃7.7 K at ∼2 GPa. No transition was detected above 2 K for 9.4 GPaP${\mathit{T}}_{\mathit{o}}$(P) about ${\mathit{P}}_{\mathit{m}}$=P(${\mathit{T}}_{\mathit{o}}^{\max }$), 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.