Magnetic properties of Yb(Rh 0.42 Co 0.58 ) 2 Si 2

In this paper, we present a comprehensive study of heat capacity, resistivity, neutron diffraction and magnetization measurements on Yb(Rh 0.42 Co 0.58 ) 2 Si 2 . Heat capacity and resistivity measurements revealed one phase transition at T m  ≈ 820 mK into the magnetically ordered phase, but in neutron diffraction experiments the magnetic intensity at the commensurate position $\tau = (\matrix{ {0.25 } & {0.75 } & {0} \cr } )$ vanished already at a lower T L  ≈ 700 mK. From magnetization measurements we could derive the existence of two magnetic phases, an antiferromagnetic phase below T L  ≈ 700 mK and an intermediate phase in the temperature range $T_{{\rm L}} < T < T_{{\rm m}} $ , which shows surprisingly ferromagnetic properties when applying magnetic fields along the [001] direction.