Magnetic properties of ZrNiAl-type R 3Mn 3GeGa 2 compounds (R = Y, Gd, Tb, Dy, Ho and Er)

Abstract

Results of magnetization measurements on R 3Mn 3GeGa 2 (R = Y, Gd, Tb, Dy, Ho, Er) compounds (hexagonal ZrNiAl-type structure; space group P 6 ¯ 2 m , No.189) and powder neutron diffraction studies on Er 3Mn 3GeGa 2 and Ho 3Mn 3GeGa 2 are presented. Magnetization data reveal that the compounds with R = Y, Tb, Dy, Ho and Er order antiferromagnetically (T N) whereas Gd 3Mn 3GeGa 2 compound shows signature of dominant ferromagnetic interactions. Y 3Mn 3GeGa 2 shows complex antiferromagnetic behaviour, whereas {Gd–Er} 3Mn 3GeGa 2 compounds show high-temperature magnetic transition that corresponds to the Mn-sublattice ordering and low-temperature magnetic transition that corresponds to the rare earth sublattice ordering which leads to complex magnetism. In applied field of 10 mT the Gd 3Mn 3GeGa 2 orders at ∼198 K ( T C). The Tb 3Mn 3GeGa 2 compound orders antiferromagnetically at T N = ∼140 K and T m = ∼20 K, respectively, whereas Dy 3Mn 3GeGa 2 shows magnetic ordering only at 54 K. In zero applied field, Ho 3Mn 3GeGa 2 has the magnetic ordering temperature at T N = 175(5) K and T m = 45(5) K, whereas Er 3Mn 3GeGa 2 show magnetic transitions at T N = 170(5) K and T m = 35(5) K. Neutron diffraction study reveals that the wave vector K 1 is [1/3, 1/3, 0] for both the compounds. However, in Ho 3Mn 3GeGa 2, the components with wave vector K 2 = [1/2, 1/2, 0] appear on both rare earth and manganese sublattices below 45(5) K. Both the manganese and rare earth magnetic moments order in a noncollinear sine modulated magnetic structure in these compounds.