Author Description

Mn5Ge3 nanoparticles were prepared by the cluster-beam deposition technique and the effects of size and surface were investigated was on their structural and magnetic properties. Nanoparticles with sizes between 7.2 and 12.6 nm were fabricated with a single-step deposition process without the need for any heat-treatment and with control over the phase purity and crystallinity by varying the argon pressure and power in the cluster gun. It was shown that all the nanoparticles crystallize in the hexagonal Mn5Si3-type crystal structure, which is also the structure of bulk Mn5Ge3. The nanoparticles of 7.2 and 10 nm were found to be superparamagnetic at room temperature (with blocking temperatures of 130 and 170 K, respectively) whereas the nanoparticles of 12.6 nm are ferromagnetic with a Curie temperature of 300 K. The magnetic properties of nanoparticles are inferior to those of bulk. The saturation magnetization, magnetocrsytalline anisotropy and coercivity at 50 K were found to increase drastically from 31 to 172 emu/cm3, 0.4 to 2.9 Mergs/cm3, and 0.4 to 1.3 kOe, respectively, as the size was increased. A core-shell particle morphology was suggested as a possible explanation of the observed magnetization decrease suggested with a 2.8-nm shell having zero magnetization which can be caused by different reasons including a possible Ge gradient and surface oxidation.