Laser Ablation Synthesis, Structure, and Exchange Bias of Mn4C/MnO Powders
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Magnetic powders containing ferrimagnetic Mn4C phase and antiferromagnetic MnO phase were prepared from a Mn-C alloy by using the laser ablation method. The Mn-C alloys were composed of Mn4C and α-Mn(C) solid solution, which decomposed into Mn4C and Mn23C6 during laser ablation. The Mn clusters precipitated from the Mn(C) solid solution were spontaneously oxidized into MnO when exposed to air, forming an exchange bias system of Mn4C/MnO with ferrimagnetic/antiferromagnetic interfaces. The exchange bias field (22.3 mT at 5 K) of the Mn4C/MnO micro-powders, which show irregular shapes and a wide size distribution in the range of ~ 100 nm to ~ 20 μm, decreases with increasing temperature. Both the interface spins and the surface spins contribute to the exchange bias effect in these powders. The coercivity of the laser-ablated micro-powders reached up to ~ 150 mT at 5 K and ~ 40 mT at 400 K, respectively.
KeywordsMn4C exchange bias laser ablation micro-powders
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We acknowledge the financial supports from the National Natural Science Foundation of China (Nos. 11074227, 51671177), and the Future Materials Discovery Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT, and Future Planning (2016M3D1A1027835).
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