Marija Milanović

Metal oxide structure, crystal chemistry, and magnetic properties

Abstract Magnetism is a force we experience every day without really being aware of it. The scientific interest in magnetism and magnetic oxides has been changed during years. The first magnetic material to be discovered was lodestone, which is better known today as magnetite (Fe3O4). The word magnet comes from the Greek word magnes, which itself may derive from the ancient colony of Magnesia (in Turkey). Magnetite was mined in Magnesia 2500 years ago. In its naturally occurring state lodestone is permanently magnetized and is the most magnetic mineral. The strange power of lodestone was well known in ancient times. Socrates (~400 BC) dangled iron rings beneath a piece of lodestone and found that the lodestone enabled the rings to attract other rings. Even earlier (~2600 BC), a Chinese legend tells of the Emperor Hwang-ti being guided into battle through a dense fog by means of a small pivoting figure with a piece of lodestone embedded in its outstretched arm. The figure always pointed south and was probably the first compass. Commercial interest in ceramic magnets started in the early 1930s with a Japanese patent describing application of copper and cobalt ferrites. The first Golden age of magnetic oxides was the 1950s and the 1960s, when the ferrites were explored and their properties optimized. Discovery of the first family of ferromagnetic oxides with a higher magnetization than ferrimagnets also dates from this period. A new age for magnetic oxides recently started, where multifunctionality, control of defects, interfaces, and thin-film device structures are the new challenges.

Probing the Transition from Nano- to Bulk-Like Behaviour in ZnFe2O4 Nanoparticles

The evolution of the magnetism as a function of the particle size is reported here for the ZnFe2O4 nanoparticles. A combination of neutron powder diffraction down to 1.5 K and magnetization measurements suggest that nanoparticles of sizes greater than about 100 nm exhibit bulk like behavior. The size dependence on magnetism can be explained by the rearrangement of the cations on the interstitial sites of the spinel cell.