Projects / Programmes
Nova osnovna stanja in kvantne kritične točke v nižjedimenzionalnih kvantnih spinskih sistemih (Slovene)
| Code |
Science |
Field |
Subfield |
| 1.02.01 |
Natural sciences and mathematics |
Physics |
Physics of condesed matter |
| Code |
Science |
Field |
| 1.03 |
Natural Sciences |
Physical sciences |
Researchers (5)
Organisations (2)
Significance for science
Detailed understanding of magnetic properties of very complex ground states in systems of frustrated antiferromagnets is one of the main challenges in solid state physics. Kagomé lattices, which are the most frustrated examples of twodimensional spin systems, have been the subject of intense research activities ever since 1951, when Syozi published his first results on magnetism in such lattice in the limit of Ising moments. The family of Langasites, which were studied in this project, is the first physical realization of strongly isotropic Kagomé lattice. It thus allowed us to directly compare the experimental results with the theoretical predictions. Results were thus of very general importance for the science of frustrated systems.
We addressed some of the most important open issues of the physics in the vicinity of special points in the phase diagram of a quantum antiferromagnet when the dimensionality is reduced to one, so that only weak couplings between 1D systems, i.e. LLs, remain. In particular, we investigated what is the nature of the quantum critical region above the quantum critical point in an array of weakly coupled LLs. We also researched how does the crossover between the 3D quantum critical regime directed by the boson description (as in the BEC), and the 1D quantum critical regime directed by the fermion description (as in the LL) take place. The nature of the crossover between the two types of ordered phases of the weakly coupled array of LLs, where the two states are defined by two different types of dominant fluctuations present in the LL has been discussed. With the discovery of new phases in BaCo2V2O8 simply controlled by the magnetic field we reproduced phase boundaries between the incommensurate and PM phases and learned that new phases correspond to columnar and ferromagnetic phases of frustrated spins on a square lattice. These results are important for a broader physics community as similar issues arise for instance in the physics of cold atoms.
The coupling between different degrees of freedom (spin, charge, orbital, …) is believed to lead to very efficient manipulation of order parameters. Magnetoelectric materials, where below certain temperature both magnetic and ferroelectric orders coexists, represent a very important class of such materials. Even though such materials were known for many years, the weakness of the coupling between the magnetization and polarization was the main obstacle for the manipulation of the magnetization with the electric field, or vice versa. In FeTe2O5Br we tried to bypass such problem in a different way. We focused on the system, where magnetic order is such, that it allows by the symmetry also ferroelectric order. Because of the presence of Te4+ lone-pair electrons the ferroelectric order is highly probable. We clearly proved, that both orders develop simultaneously at exactly the same transition temperature. This was already the first indication for the strong magnetoelectric coupling in this system, which was further demonstrated in dielectric measurements at high magnetic fields, where we discovered large changes in the dielectric constant. In other words, we manipulated the ferroelectric order by magnetic field. Such manipulation is also of interest for possible future applications, such as for instance writing the information with the magnetic field while reading it with the electric field. Magnetoelectric order in FeTe2O5Br represents a new class of magnetoelectrics and its discovery represents an important contribution to the physics of magnetic and ferroelectric materials. In addition, our discovery of “persistent spin dynamics” down to 20 mK can offer a completely new look at the unconventional spin dynamics in strongly frustrated magnetic systems.
Significance for the country
1. Transfer of knowhow to Slovenia:
Although we did not expect that our project will lead to any direct applications, we still believe that the results will be of general importance for the society. Namely, based on the way we have designed the dissemination workpackage it is clear that we mainly tried to foster links between Slovenian research groups and leading European laboratories. In 2010 we have thus organized the international workshop “Magnetic resonance in highly frustrated magnetic systems”, Kranjska Gora, Slovenia.
Dissemination of knowledge was therefore very high on a list of our priorities in this project. In addition we established close collaborations with the following research groups:
a) Laboratory for Novel Electronic States: NMR, MuSR and photoemission, Laboratoire de
Physique des Solides (LPS), Orsay, France (head Prof. Dr. P. Mendels),
b) Grenoble High Magnetic field Laboratory, CNRS, Grenoble, France (head Prof. Dr. C.
Berthier).
c) National High Magnetic Field Laboratory, Talahasse, ZDA (head, prof. dr. Hans van Tol)
Knowhow, which was accumulated during joint research activities, was successfully
transferred to Slovenia with a special emphasis on the involvement of young researchers.
For the project team it was extremely important to keep contacts with such prominent
laboratories with an excellent track record and state-of-the-art equipment. We would
especially like to mention at this point experiments in high magnetic fields that were conducted in Grenoble and Tallahassee and that could not have been performed in Slovenia, since at the moment we still do not have such equipment. We will continue to collaborate with these groups also in the future.
2. Involvement of young researchers:
We have very successfully integrated young researchers into the project team. These
researchers gained special know-how (Engineering skills acquired during the development of research equipment) and experience that would be potentially
interesting also for the Slovenian industry. They acquired profound knowledge in the field of magnetism, nanotechnology, and measurements in physics.
Finally we mention, that major part of the PhD work of dr. Matej Pregelj has been linked with the project activities. Another candidate Anton Potočnik will defend his PhD in 2013. We have also successfully integrated undergraduate students of physics from the University of Ljubljana - some of them finished their diploma works under our supervision.
3. Involvement into international projects:
Based on the results of published reports in international journals and conferences, we
were invited to the COST project, which was in 2009 still under evaluation. This integration into international networks is a direct consequence of our participation in the ESF network »Highly frustrated magnetism«, where professor Denis Arčon was an active member of the program committee. In 2011 we started with the FP7 LEMSUPER project (www.lemsuper.eu).
4. Development of new experimental techniques:
As we have originally planned, we managed to develop and test new high-pressure
NMR and EPR cells, which can currently operate at pressures up to 1.5 GPa. With these cells we have used some very innovative solutions. As an example of such innovation we bring here the attention to the use of dielectric resonators in EPR high-pressure
cell, which significantly improved the sensitivity of our microwave system. We stress that such experimental equipment was not available in Slovenia so far and we anticipate that it will give us access to some new magnetic phases and phenomena, when applied to physical systems of interest in the future.
Most important scientific results
Annual report
2009,
2010,
2011,
final report,
complete report on dLib.si
Most important socioeconomically and culturally relevant results
Annual report
2009,
2010,
2011,
final report,
complete report on dLib.si
