A study of the new ferromagnetic YbMn6Sn6 compound by magnetization and neutron diffraction measurements

Bulk magnetization and neutron diffraction experiments have been performed on the new ternary stannide YbMn6Sn6. This compound crystallizes with a hexagonal structure which can be described as an intermediate ordered state between the HfFe6Ge6- and the YCo6Ge6-type structures, with cell parameters revealing the abnormal behavior of the Yb ion (close to a divalent state) in this compound. The magnetometric measurements show that YbMn6Sn6 is ferromagnetic below T-c = 300(5) K with a maximum magnetization value of M-max = 13.56 mu(B)/f.u. at 4.2 K. The neutron diffraction study leads to a simple ferromagnetic arrangement of ferromagnetic easy-plane Mn(0 0 1) planes without ordering of the Yb sublattice down to 2 K. The Mn magnetic moment increases from mu(Mn) = 0.90(16) mu(B) at 295 K up to Phm = 2.35(6) mu(B) at 2 K. Moreover, we also publish the results of the neutron diffraction study of the already known ferromagnetic (T-c = 290(5) K) HfFe6Ge6-type MgMn6Sn6 compound which adopts the same magnetic arrangement of the Mn sublattice than YbMn6Sn6 with an Mn moment value of mu(Mn) = 2.32(4) mu(B) at 2 K. (C) 1999 Elsevier Science B.V. All rights reserved.