INVESTIGATION OF THE MAGNETIZATION REVERSAL MODE FOR INDIVIDUAL ELLIPSOIDAL SINGLE-DOMAIN PARTICLES OF GAMMA-FE2O3

We report measurements of the angular dependence of the switching fiel d of individual ellipsoidal single-domain ferromagnetic particles. The measurements were carried out by Lorentz magnetometry on submicromete r gamma-Fe2O3 particles and provide insights into the magnetization re versal for individual ellipsoidal particles of known morphology. The f unctional form of the switching field data indicates that the particle s reverse by curling over a narrow range near 0 degrees and by coheren t rotation at all larger angles. A value of 3+/-2x10(-7) erg/cm for th e exchange constant of the gamma-Fe2O3 is obtained from these measurem ents. We suggest that the long desired goal of complete characterizati on of the magnetic properties of individual single-domain particles is now feasible.