Spin-glass-like behavior of surfactant capped Co50Ni50 nanoparticles

We investigated static and dynamic magnetic properties of surfactant capped 25 nm Co50Ni50 particles. These nanoparticles exhibit the superparamagnetic behavior at 300 K. Interestingly, a freezing temperature (Tf ∼ 16 K) is observed in the ZFC curve, which corresponds to surface spin-glass-like transition. The significant high coericivity (Hc ∼ 910 Oe) is observed at 5 K as compared to Hc ∼ 180 Oe at 77 K and is attributed to the random freezing of surface spins at T ⩽ Tf. The spin-glass-like behavior of nanoparticles is further verified by ac-susceptibility measurements as a function of temperature at different frequencies. The fits of Arrhenius law, Vogel–Fulcher law and dynamic scaling equation to data confirm the spin-glass-like behavior of Co50Ni50 nanoparticles.