Beating Thermal Deterioration of Magnetization with Mn₄C and Exchange Bias in Mn⁻C Nanoparticles.

The magnetization of most materials decreases with increasing temperature due to thermal deterioration of magnetic ordering. Here, we show that Mn₄C phase can compensate the magnetization loss due to thermal agitation. The Mn⁻C nanoparticles containing ferrimagnetic Mn₄C and other Mn⁻C/Mn-O phases were prepared by using the traditional arc-discharge method. A positive temperature coefficient of magnetization (~0.0026 Am² kg ^-1 K ^-1 ) and an exchange bias up to 0.05 T were observed in the samples. We ascribe the exchange bias to the co-existence of ferrimagnetic Mn₄C/Mn₃O₄ and antiferromagnetic α-Mn(C)/MnO phases. The positive temperature coefficient of magnetization of the samples was ascribed to the presence of Mn₄C phase, which is considered as a Néel's P -type ferrimagnet.