Magnetic phase diagram of Y1−xTbxMn6Sn6 compounds

The Y1−xTbxMn6Sn6 compounds (x=0, 0.175, 0.2, 0.225, 0.25) were studied by small angle neutron scattering (SANS) and paramagnetic neutron spin echo. The YMn6Sn6 compound is found to be a helimagnet in the whole temperature range below TN=310 K. Close to TN an additional peak of a Lorenz shape was observed at Q=0. The peak is thought to have originated from the ferromagnetic fluctuations of the magnetic Mn moment in the ab-plane of the hexagonal crystal structure. Compounds, in which Y is replaced by Tb, change their magnetic order with the increase of temperature: from easy cone ferromagnetic phase at low T through the helicoidal phase to the ferromagnetic fluctuation close to TN. Temperature-concentration phase diagram of Y1−xTbxMn6Sn6 is built on the basis of the obtained data.