Crystal structure and magnetic ordering in ErFe 6Ge 6 studied by X-ray, neutron diffraction and magnetic measurements

Abstract

The crystal structure and magnetic ordering of ErFe 6Ge 6 were studied by means of X-ray and neutron powder diffraction and on a single crystal. Our results suggest that ErFe 6Ge 6, when annealed after casting, adopts a crystal structure intermediate between the perfectly ordered HoFe 6Sn 6 structure type, and the disordered structure of the YCo 6Ge 6 type. The 293 K (high resolution) and the 4.5 K neutron data show that the antiferromagnetic reflections can be explained by a 2× c cell enlargement of the YCo 6Ge 6-type unit cell. The collinear antiferromagnetic magnetic structure is composed of ferromagnetic Fe-sheets coupled antiferromagnetically along the c h-axis. The Er moments become ordered only below 3 K. This ordering is ferromagnetic with the Er-moments directed along the a h-axis. The fact that the ferromagnetic and the antiferromagnetic ordering types are described by two different magnetic space groups indicates the presence of two order parameters, which explains the independent behaviour of the Fe and Er sublattices.