Probing Magnetic Ordering in Magnetite Nanoparticles using x-rays*

Understanding the nanoscale magnetic properties of magnetic nanoparticles is crucial for their applications in nanotechnologies and in medicine. While macroscopic properties of magnetic nanoparticles have been extensively studied via magnetometry, information about the nanoscale magnetic order is often lacking. We will see how the nanoscale magnetic order can be revealed by x-rays using the technique of x-ray resonant magnetic scattering. Scattering profiles collected under different conditions of magnetic field and at different temperatures will be presented. We will see how the magnetic orders at low magnetic field values, near to remanence, strongly depend on particle size.  Smaller 5 nm particles exhibit a random superparamagnetic behavior, whereas bigger 11 nm particles show antiferromagnetic correlations.