170Yb Mössbauer and neutron diffraction measurements on spin-chain Yb2BaNiO5

The Ni (S = 1) chain compound Yb 2 BaNiO 5 (space group: Immm) is the end magnetic member of the isomorphous rare earth series. We have studied its magnetic properties using 170 Yb Mossbauer spectroscopy and neutron diffraction. Magnetic order is induced into the Ni 2+ chains through the polarization of the Yb 3+ and leads to an ordering temperature of 8.8 K. The Ni 2+ moments, saturated value 1.1 μ B , are antiferromagnetically aligned close to the c-axis and the Yb 3+ moments, saturated value 0.6 μ B , are antiferromagnetically aligned at an angle of 55 to the c-axis and close to the (ac) plane. The thermal evolution of the Yb 3+ moment is well described with a phenomenological molecular-field model. The value derived for the effective polarizing field acting on the Ni 2+ when expressed per Yb 3+ moment is much higher than the equivalent value for any of the other rare earths.