Magnetic resonance investigation of the particle-particle equilibrium distance within small agglomerates in magnetic fluids

Magnetic resonance spectra of magnetic fluids in a wide particle volume fraction range were investigated at room temperature. The analysis of the spectra showed contributions due to magnetic centers located in isolated nanoparticles and dimers. The resonance field decreases as the particle concentration increases, until the resonance field reaches a minimum value at a critical concentration. Above this critical concentration the opposite behavior has been observed. The data is explained using a model that allowed us to calculate the particle-particle equilibrium distance within small agglomerates.