Unusual Yb magnetic properties in YbMn_6Ge_(1.8-x)Sn_(4.2)Ga_x and YbMn_6Ge_(1.8)Sn_(4.2-y)Ga_y

摘要

We investigate the magnetic properties of the new HfFe_6Ge_6-type (P6/mmm) YbMn_6Ge_(1.8-x)Sn_(4.2)Ga_x (x=0.05, 0.4 and 0.9) and YbMn_6Ge_(1.8)Sn_(4.2-y)Ga_y (y=0.05,0.5 and 1.0) alloys from DC magnetization and powder neutron diffraction experiments. The electronic structure modifications induced by the Ga substitution are found to promote the ferromagnetic order of the Mn sublattice, to enhance the Yb ordering temperature (up to T_(Yb)～170 K) and to strongly increase the low-temperature coercive field (up to μ_0H_c～1 T). By contrast the changes in the Yb magnetic moment magnitude upon Ga substitution are analyzed to be mainly driven by chemical pressure effects. The reduced Yb magnetic moment (1.0 μ_B ＜ m_(Yb) ＜ 1.8 μ_B) compared with the free ion value (4 μ_B) is interpreted as resulting from Kondo screening. There are strong indirect indications that the high temperature Yb magnetic ordering likely involves intermediate valent Yb.