Beating Thermal Deterioration of Magnetization with Mn ₄C and Exchange Bias in Mn–C Nanoparticles

Abstract

The magnetization of most materials decreases with increasing temperature due to thermal deterioration of magnetic ordering. Here, we show that Mn ₄C phase can compensate the magnetization loss due to thermal agitation. The Mn–C nanoparticles containing ferrimagnetic Mn ₄C and other Mn–C/Mn-O phases were prepared by using the traditional arc-discharge method. A positive temperature coefficient of magnetization (~0.0026 Am ² 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 Mn ₄C/Mn ₃O ₄ and antiferromagnetic α-Mn(C)/MnO phases. The positive temperature coefficient of magnetization of the samples was ascribed to the presence of Mn ₄C phase, which is considered as a Néel’s P-type ferrimagnet.