Magnetism of MnGa-based nanostructures*

Materials with high magnetic anisotropy and Curie temperature well above room temperature have potential for a range of applications including high-density recording, nonvolatile memory and permanent-magnet materials. Mn$_{\mathrm{y}}$Ga (1 $\le $ y $\le $ 2) is one such compounds that can be synthesized in the tetragonal L1$_{0}$ or D0$_{22}$ structures based on the value of y in Mn$_{\mathrm{y}}$Ga. Our experimental investigation of the rapidly quenched nanostructured ribbons shows that the material with y $=$1.2, 1.4 and 1.6 prefers the L1$_{0}$ structure and that with y $=$1.9 and 2.1 prefers D0$_{22}$ structure. We have found a maximum saturation magnetization of 88 emu/g in Mn$_{1.2}$Ga which decreases monotonically to 50 emu/g as y reaches 2.1. Although both the L1$_{0}$ and D0$_{22}$Mn$_{\mathrm{y}}$Ga samples show a high Curie temperature (T$_{\mathrm{c}})$ well above room temperature, the value of T$_{\mathrm{c}}$ decreases almost linearly from 740 K for Mn$_{2.1}$Ga to 550 K for Mn$_{1.2}$Ga. We will also discuss the effect of boron doping on the structural and magnetic properties of this material.