Seminár z fyziky kondenzovaných látok - Jaroslav Tóbik (20.3.2025)
vo štvrtok 20.3.2025 o 13:00 v posluchárni F1 108
Prednášajúci: Ing. Jaroslav Tóbik, PhD. (Elektrotechnický ústav SAV)
Názov: Ferrotorroidal order by spontaneous symmetry breaking
Termín: 20.3.2025, 13:00 hod., F1/108
Abstrakt:
The development of technology makes it possible to fabricate artificial structures on a sub-micrometer scale with a good definition of building elements. The periodic repetition of the patterned elements defines a crystal. Thus, technology allows us to build artificial materials with properties that are not observed in natural materials. In the field of applied magnetism, there is vivid research in artificial structurally periodic arrays of magnetic elements. However, these structures usually have a non-periodic magnetic pattern. There are numerous reasons for difficulties in achieving magnetic order. The main obstacle is the presence of many local minima and large energy barriers among them. The energy barriers are usually much higher than the achievable thermal energy. Therefore, thermally activated magnetization flipping is possible only during the growth process when the thickness of the magnetic material is about 1 nm. Then, the magnetic structure freezes. The magnetic state ma- nipulation afterwards is problematic, especially in cases when the ground state has no net magnetization, as in the case of ferrotoroic order. To tackle this problem we suggested new demagnetization protocol. It is based on magnetizing the structures into out-of-plane direction. Naive expectation is that the tilt of the magnetization into out-of-plane direction will only renormalize energy landscape. More detailed analysis shows, that by this procedure the ferrotoroic state is the only stable state in the basic unit cell for certain interval of external magnetic field. Thus appearance of stable and metastable magnetic states in some structures can be described as a serie of symmetry breaking processes. This theory was verified by experiments with rather convincing results.