Néel relaxation occurs when the magnetic moment of a nanoparticle overcomes an energy barrier due to thermal energy, causing it to switch direction. The energy barrier is determined by the volume of the nanoparticle and the magnetic anisotropy of the material. The relaxation time, or the time it takes for the magnetic moment to flip, is given by the Arrhenius law: τ = τ₀ exp(KV/kT) where τ is the relaxation time, τ₀ is the attempt time, K is the anisotropy constant, V is the volume of the nanoparticle, k is the Boltzmann constant, and T is the temperature. This equation indicates that smaller particles or higher temperatures result in shorter relaxation times.
