Magnetic Order in CeGe$_{1.76}$ studied by neutron diffraction on single crystals*

The CeGe$_{1.76}$ compound shows a very interesting magnetic behavior with a rich set of features in magnetization measurements indicative for several antiferromagnetic and ferromagnetic transitions at low temperatures. In this report we will present our recent neutron diffraction studies on a CeGe$_{1.76}$ single crystal performed at the instrument HB-1A, High-Flux Isotope Reactor, Oak Ridge. We revealed a complex magnetic phase diagram: Below approx. 7 K, the magnetic Ce moments order in an antiferromagnetic structure with an incommensurate propagation along the c direction. The major component of the ordered moment is aligned along the b direction. Detailed temperature-dependent scans along the c direction show a lock-in to a commensurate antiferromagnetic order around 5.5 K connected with a squaring up of the ordered moments indicated by the occurrence of higher harmonic satellite Bragg peaks. Below 4 K additional Bragg peaks occur indicative of a second coexisting type of magnetic order with small moments aligned along the a or c direction. Further experiments are necessary to conclude the determination of this complex magnetic ordering in the CeGe$_{1.76}$ compound.