Magnetic properties of ZrNiAl-type R3Mn3SiGa2 compounds (R = Y, Gd, Tb, Dy and Ho)

Magnetic properties of R3Mn3SiGa2 (R = Y, Gd, Tb, Dy, Ho) compounds (hexagonal ZrNiAl-type structure; space group P6¯2m, No.189) have been studied. Powder neutron diffraction results on Tb3Mn3SiGa2, Dy3Mn3SiGa2 and Ho3Mn3SiGa2 compounds are presented. Magnetization data on Gd3Mn3SiGa2 sample reveal a transition at about 155 K (TN) and an anomaly at 44 K whereas the compounds with R = Tb, Dy, Ho and Y order magnetically at 125 K, 55 K, 60 K and 163 K respectively, in 0.5 T applied field. Magnetization has linear field dependence at 5 K for all these compounds. Neutron data in zero applied field reveal three magnetic transitions for Tb3Mn3SiGa2 compound: at Tm1ND∼180 K, Tm2ND=90 K and Tm3ND=40 K respectively, whereas the Ho3Mn3SiGa2 compound shows magnetic transitions at Tm1ND∼165 K, Tm2ND∼80 K and Tm3ND=40 K. Neutron diffraction study reveals that the magnetic structure is antiferromagnetic cone with wave vectors K1 = [1/3, 1/3, 0], K2 = [1/2, 1/2, 0] for both the compounds. The magnetic structure of Dy3Mn3SiGa2 is also an antiferromagnetic cone but with wave vector K2 = [1/2, 1/2, 0]. The low temperature magnetic transition is attributed to a possible spin reorientation process.