Structure and Magnetism of Mn5Ge3 Nanoparticles

Authors

Onur Tosun, University of DelawareFollow
Mohammed Salehi-Fashami, University of DelawareFollow
Balamurugan Balasubramanian, University of Nebraska-LincolnFollow
Ralph Skomski, University of Nebraska-LincolnFollow
David J. Sellmyer, University of Nebraska - LincolnFollow
George C. Hadjipanayis, University of Delaware, NewarkFollow

Date of this Version

2018

Citation

Nanomaterials 2018, 8, 241

Comments

© 2018 by the authors.

Open access

doi:10.3390/nano8040241

Abstract

In this work, we investigated the magnetic and structural properties of isolated Mn₅Ge₃ nanoparticles prepared by the cluster-beam deposition technique. Particles with sizes between 7.2 and 12.6 nm were produced by varying the argon pressure and power in the cluster gun. X-ray diffraction (XRD)and selected area diffraction (SAD) measurements show that the nanoparticles crystallize in the hexagonal Mn₅Si₃-type crystal structure, which is also the structure of bulk Mn₅Ge₃. The temperature dependence of the magnetization shows that the as-made particles are ferromagnetic at room temperature and have slightly different Curie temperatures. Hysteresis-loop measurements show that the saturation magnetization of the nanoparticles increases significantly with particle size, varying from 31 kA/m to 172 kA/m when the particle size increases from 7.2 to 12.6 nm. The magnetocrystalline anisotropy constant K at 50 K, determined by fitting the high-field magnetization data to the law of approach to saturation, also increases with particle size, from 0.4 × 10⁵ J/m³ to 2.9 × 10⁵ J/m³ for the respective sizes. This trend is mirrored by the coercivity at 50 K, which increases from 0.04 T to 0.13 T. A possible explanation for the magnetization trend is a radial Ge concentration gradient.