Magnetic properties of Fe3O4 nano-hollow spheres

We prepared magnetite nano-hollow spheres with diameter 100-725 nm using solvothermal method. We studied the magnetic domain structures of the spheres and found them to vary from single domain for smaller diameter to multi-domain structure for the spheres of larger diameter. We also reported the frequency dependence of their magnetic properties and interestingly, found a systematic power law variation in coercivity and hysteresis loss with frequency, magnetic field strength and also with hollow sphere diameter. The results clearly represent that the domain wall width or the number of domains depends not only on the sphere diameter but also on the applied field frequency.