Weak ferromagnetism and spin-glass state with nanosized nickel carbide

Magnetic properties of Ni3C nanoparticles, about 40 nm in diameter, have been investigated. The sample exhibits weak ferromagnetic (FM), spin-glass (SG), and paramagnetic (PM) properties by alternating current susceptibility and direct current magnetization measurements. The freezing temperature of the SG phase at zero applied field is determined as TF0∼11.0 K. At T>TF0, a very weak ferromagnetism has been observed over a strong PM background. The Curie temperature TC is shown to exceed 300 K, and the ferromagnetism at 300 K is determined as about 0.02 emu/g∼6.7×10−4 μB per Ni3C formula unit. An anomalous dip appears in the temperature dependent coercivity HC(T) near the freezing temperature TF0. It reflects the distortedly reduced coercivity in the M(H) hysteresis loop measured at T∼TF0 with the applied sweeping field approaching H=0. This is attributable to the interaction between the SG and the weak FM phases. The possible origin of the magnetic moments that account for the observed FM, SG, and PM prop...