Nonlinear magnetic stochastic resonance: Noise-strength-constant-force diagrams

Signal-to-noise properties of a periodically driven noisy magnetic bistable system-superparamagnetic particles with uniaxial anisotropy-are investigated in the framework of the Fokker-Planck equation solved both analytically and numerically. The system is subject to a constant (bias) field that imparts even harmonics into its low-frequency magnetic spectrum. A comparative study of the linear and quadratic susceptibilities and stochastic resonances (SR) is carried out. We show that the quadratic SR is much sharper than the linear one and unlike the latter is essentially frequency dependent.