Magnetism and electron transport of MnyGa (1 < y < 2) nanostructures

Nanostructured Mn y Ga ribbons with varying Mn concentrations including Mn 1.2 Ga, Mn 1.4 Ga, Mn 1.6 Ga, and Mn 1.9 Ga were prepared using arc-melting and melt-spinning followed by a heat treatment. Our experimental investigation of the nanostructured ribbons shows that the material with y ¼ 1.2, 1.4, and 1.6 prefers the tetragonal L1 0 structure and that with y ¼ 1.9 prefers the D0 22 structure. We have found a maximum saturation magnetization of 621 emu/cm 3 in Mn 1.2 Ga which decreases monotonically to 300 emu/cm 3 as y reaches 1.9. Although both the L1 0-and D0 22-Mn y Ga samples show a high Curie temperature (T c) well above room temperature, the value of T c decreases almost linearly from 702 K for Mn 1.9 Ga to 551 K for Mn 1.2 Ga. All the ribbons are metallic between 2 K and 300 K but the Mn 1.2 Ga also shows a resistance minimum near 15 K. The observed magnetic properties of the Mn y Ga ribbons are consistent with the competing ferromagnetic coupling between Mn moments in the regular L1 0-MnGa lattice sites and antiferromagnetic coupling with excess Mn moments occupying Ga sites.