Magnetic nanoparticles appear naturally in rock magnetism together with a large distribution of sizes and shapes. They have numerous applications from nano-size magnetic memories to metamaterials for electromagnetic waves as well as biological applications such as nanosurgery with minimal traumatism. Their long-ranged size- and shape-dependent dipolar interactions provide numerous useful properties. This book describes the preparation as well as the magnetic properties of nanoparticles and also considers 2D dots, nearly spherical samples, elongated samples, and various assemblies of nanoparticles. The authors report the static magnetic structures and dynamic properties of these nanoparticles and the topological defects in 2D and 3D nanoparticles with new examples of S-shaped vortex or antivortex and of bent vortex or antivortex in 3D nanoparticles. The spectrum of magnetic excitations is shown to exhibit the occurrence of gaps, a key for magnonic metamaterial devices. Magnetic excited states are also considered with their coupling to nanoparticle elastic properties.
