Magnetic Mn 5 Ge 3 nanocrystals embedded in crystalline Ge: a magnet/semiconductor hybrid synthesized by ion implantatio
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NANO EXPRESS
Open Access
Magnetic Mn5Ge3 nanocrystals embedded in crystalline Ge: a magnet/semiconductor hybrid synthesized by ion implantation Shengqiang Zhou1*, Wenxu Zhang2*, Artem Shalimov1, Yutian Wang1,3, Zhisuo Huang2, Danilo Buerger1, Arndt Mücklich1, Wanli Zhang2, Heidemarie Schmidt4 and Manfred Helm1,3
Abstract The integration of ferromagnetic Mn5Ge3 with the Ge matrix is promising for spin injection in a silicon-compatible geometry. In this paper, we report the preparation of magnetic Mn5Ge3 nanocrystals embedded inside the Ge matrix by Mn ion implantation at elevated temperature. By X-ray diffraction and transmission electron microscopy, we observe crystalline Mn5Ge3 with variable size depending on the Mn ion fluence. The electronic structure of Mn in Mn5Ge3 nanocrystals is a 3d6 configuration, which is the same as that in bulk Mn5Ge3. A large positive magnetoresistance has been observed at low temperatures. It can be explained by the conductivity inhomogeneity in the magnetic/semiconductor hybrid system. Keywords: Mn5Ge3, Ion implantation, Magnetic nanocrystals, Magnetoresistance
Background Due to its compatibility to Si technology, Ge has attracted special attention as a host semiconductor for diluted magnetic impurity atoms. However, due to the low solid solubility of transition metals in Ge, intermetallic compounds (mainly Mn5Ge3) tend to form in the Ge host [1-6]. Mn5Ge3 is a half metallic ferromagnet with a large spin polarization [7]. By first principle calculation, large spin injection efficiency is expected by the integration of Mn5Ge3 within the Ge matrix [7]. Electrical spin injection and detection in Ge have been experimentally demonstrated [8,9]. Therefore, considerable work has been done to fabricate epitaxial Mn5Ge3 films as well as nanostructures [10-12]. The Curie temperature (TC) of Mn5Ge3 is 296 K, which can be effectively increased by carbon doping. Spiesser et al. reported the epitaxial growth of Mn5Ge3Cx films on Ge (111) [13]. When x is around 0.6, TC can be as high as 430 K. On the other hand, some unknown nanoscale * Correspondence: [email protected]; [email protected] 1 Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, PO Box 510119, Dresden 01314, Germany 2 State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China Full list of author information is available at the end of the article
Mn-rich phases also form under particular conditions during molecular beam epitaxy (MBE) growth [14-19]. Those nanostructures can have a TC much higher than 300 K. Besides MBE, ion implantation has been used to prepare ferromagnetic semiconductors as well as hybrids of ferromagnets embedded in semiconductors [20-24]. The advantages of ion implantation include compatibility with conventional Si-chip technology and lateral patterning. Patterning by ion implantation allows the synthesis of magnetic structures comprising different magnetic phases. By carbon implant
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