Investigation of the magnetization reversal mode for individual ellipsoidal single-domain particles of γ-Fe₂O₃

We report measurements of the angular dependence of the switching field of individual ellipsoidal single-domain ferromagnetic particles. The measurements were carried out by Lorentz magnetometry on submicrometer γ-Fe 2O3 particles and provide insights into the magnetization reversal for individual ellipsoidal particles of known morphology. The functional form of the switching field data indicates that the particles reverse by curling over a narrow range near 0 degrees and by coherent rotation at all larger angles. A value of 3±2×10-7 erg/cm for the exchange constant of the γ-Fe2O3 is obtained from these measurements. We suggest that the long desired goal of complete characterization of the magnetic properties of individual single-domain particles is now feasible.