Evidence of spin reorientation in YbFe6Ge6 from neutron diffraction and Fe-57 Mossbauer experiments

High-resolution neutron diffraction and Fe-57 Mossbauer experiments have be en performed on powder samples of the ternary intermetallic YbFe6Ge6. This compound crystallizes with a hexagonal structure (P6/mmm) which can be desc ribed as an ordered state intermediate between the HfFe6Ge6- and YCo6Ge6-ty pe Structures; with cell parameters suggesting that the Yb ion is in (or cl ose to) a trivalent state. At room temperature, the Fe-sublattice magnetic arrangement consists of an antiferromagnetic stacking along the c-axis of t he ferromagnetic (001)Fe planes with the easy direction of magnetization al ong [001]. Below about 85 K a spin-reorientation process occurs; a fraction gamma(T) of the iron moments rotate abruptly from the c-axis to a given di rection in or close to the basal plane. This phenomenon allows the observat ion of anisotropic contributions to the total hyperfine held at the Fe site . At 4.2 K, approximately 18% of the iron moments remain along the c-axis. No long-range magnetic order of the Yb sublattice is observed, at least abo ve 1.5 K. We also report Fe-57 Mossbauer investigations of the HfFe6Ge6-typ e LuFe6Ge6 compound.