We investigated static and dynamic magnetic properties of surfactant capped 25nm Co 50 Ni 50 particles. These nanoparticles exhibit the superparamagnetic behavior at 300K. Interestingly, a freezing temperature (T f ∼16K) is observed in the ZFC curve, which corresponds to surface spin-glass-like transition. The significant high coericivity (H c ∼910Oe) is observed at 5K as compared to H c ∼180Oe at 77K and is attributed to the random freezing of surface spins at T⩽T f . 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 Co 50 Ni 50 nanoparticles.