Thin films of multiferroic spinel CoCr2O4

It is expected that the tremendous growth of data storage capacity will increase in the future. Thus smaller, faster and cheaper memories are desired. A common technology for information storage is the use of hard discs, which store data in small magnetic domains with two possible states: with the magnetic north or south pole pointing upwards. The information can be “written” by orienting the domains by a magnetic field, after which the orientation is stable in time.
To generate such magnetic field, a magnetoelectric coil is used. With such a coil it is difficult to make a magnetic field that is strong enough to switch the magnetic bit, but confined enough to prevent neighboring bits from switching. In addition, the electromagnet uses high currents, resulting in overheating, especially at high bit density. An alternative could be substituting common magnets by materials that present so-called magnetoelectric coupling, that is materials in which the ionic and magnetic structures are intimately coupled such that it is possible to switch the magnetization by an electric field. If these materials, in addition, display two state polar states (electrical dipoles pointing up or down) next to two stable magnetic state (so-called multiferroics), then a four-state memory is possible, allowing higher density of data storage.
The synthesis of magnetoelectric multiferroic thin films is, despite of its crucial importance in spintronics and electronics, rarely reported. The growth and properties of thin films of unprecedented quality of the multiferroic material CoCr2O4 are described in this thesis.