Ferromagnetic quantum phase transition in Co(S 1- x Se x ) 2 system

In Co(S 1- x Se x ) 2 system, a transition from ferromagnetic to paramagnetic state occurs near x = 0.11. In order to research the physical properties of the samples near this transition, polycrystalline samples of Co(S 1- x Se x ) 2 (0.0≤ x ≤0.16) were prepared. And their structure and resistivity were measured. It is found that the ferromagnetic transition temperature T C is suppressed by Se doping in the relation T C ～(1- x ) 1/2 . And the ferromagnetic phase transition goes from the second to the first order. The temperature dependence of resistivity, ρ ( T ), shows a Fermi-liquid behavior, ρ ( T )=ρ 0 + AT 2 , in Co(S 1- x Se x ) 2 ( x ρ ( T ) occurs in the samples near a critical concentration x =0.11. It is suggested that the phase transition near x =0.11 is a quantum phase transition, and the quantum critical spin fluctuation at zero temperature results in non-Fermi liquid behavior.