Studium kritických jevů v blízkosti trikritických bodů

• Thesis title in Czech: Studium kritických jevů v blízkosti trikritických bodů
• Thesis title in English: Character of criticality in the vicinity of tritricical points
• Key words: magnetismus|kritické chovani|trikritický bod|fázový diagram
• English key words: magnetism|criticality|tricritical point|phase diagrams
• Academic year of topic announcement: 2024/2025
• Thesis type: diploma thesis
• Department: Department of Condensed Matter Physics (32-KFKL)
• Supervisor: doc. RNDr. Jan Prokleška, Ph.D.
• Advisors: doc. RNDr. Jiří Pospíšil, Ph.D.

Guidelines

1. Seznámení se se studovanými materiály
2. Proměření základních veličin podél fázové hranice (napříč trikritickým bodem) na vybraném materiálu, analýza jejich kritického chování, srovnání s existujícími modely.
3. Diskuse získaných dat, sepsání diplomové práce.

References

- aktuální publikace k tématu a vybraným materiálům
- Tricritical fluctuations and elastic properties of the Ising antiferromagnet UIrSi3 T. N. Haidamak, J. Valenta, J. Prchal, M. Vališka, J. Pospíšil, V. Sechovský, J. Prokleška, A. A. Zvyagin, and F. Honda, Phys. Rev. B 105, 144428
- N. W. Ashcroft, N. D. Mermin: Solid State Physics, Saunders College, Philadelphia 1976.
- Ch. Kittel: Úvod do fyziky pevných látek, Academia, Praha, 1985.

Preliminary scope of work in English

Critical phenomena have been one of the most studied issues of physics since the critical points were discovered almost 150 years ago. The continuous (second-order) phase transitions are connected with unified behavior near and at the critical point which can be described by critical exponents. The universal behavior near critical points was described by the renormalization group theory. For continuous phase transitions, the behavior close to the critical point (Tc ) (i.e., the critical
exponents) depends only on a few parameters:
– dimensionality of the order parameter n
– dimensionality of the system d
– range of the interaction — long-range (power-law decay r−n ) vs short-range
(exponential decay e−r/r0 )
Experiments show that the relevant thermodynamic variables exhibit power-law dependencies on the parameters specifying the distance (i.e., as a function of reduced temperature) from the critical point. It is desirable to investigate how a certain universal critical behavior and magnetic dimensionality are related to a given material’s particularities (symmetry of crystal structure, hierarchy, and anisotropy of magnetic interactions, degree of localization of “magnetic” electrons, etc.).
Based on the analysis of heat capacity measurements in the magnetic field, we recently explained (T. Haidamak et al., 2022) the significant anomalies at the second-order branch of the phase transition boundary as a manifestation of the tricritical fluctuations, dominating the region below the tricritical point. The outcome confirms the 3D Ising model, at zero and low magnetic fields, with a crossover to the mean-field tricritical behavior at fields close to the tricritical point, where tricritical fluctuations dominate the temperature evolution of the given property.
The broader aim of the thesis is to replicate this approach in selected systems and/or properties and observe how far this behavior is generic or rare among various types of magnetic systems.

The experiments will be done in MGML (www.mgml.eu).