Research of frustrated systems from the point of view of the Jurčišin couple

SAS award for the scientific work in 2019 was given to RNDr. Marián Jurčišin, PhD. and RNDr. Eva Jurčišinová, PhD., members of the Department of Theoretical Physics at the Institute of Experimental Physics SAS. The aim of their research can be (now exaggerating) a reason for frustration for many laymen. The award was received “for the results attained in the field of thermodynamic properties of frustrated magnetic systems”.

The first question was quite obvious: How can magnetic systems be frustrated at all and what is the connection with human frustration? Moreover, if the systems are thermodynamic, how can they be frustrated? Scientific couple just smiled and began to explain.

“Excellent question. Person can feel frustrated if he or she can not satisfy or fulfill different but equally important needs at the same time because they contradict each other. Magnetic frustrated systems have very similar problem. Due to nature of internal interactions or the geometric structure of the crystal lattice, there are conflicts in magnetic alignment and therefore the system is unable to create an unambiguous arrangement of its ground states; thus they are ‘frustrated’,” explains Marián Jurčišin. He adds, that there are many arrangements with lowest energy and therefore we say that these states are highly degenerate.

“It is the existence of these highly degenerate ground states that is the hallmark of the presence of magnetic frustration, which is responsible for the non-trivial thermodynamic properties observed in the magnetic frustrated systems.” To put it simply – magnetic frustrated systems behave in an unusual and unconventional way. This is why they are subject of many research projects, several of them at Institute of Experimental Physics SAS. Are they therefore something “really special”?

“Frustrated magnetic materials are studied theoretically as well as experimentally for their interesting and unique properties, which have not been observed in any other magnetic systems,” explains Eva Jurčišinová. The effort to gain these unique properties of frustrated magnetic systems on a fundamental theoretical base was and still is the main reason for scientists to carry out the detailed research.

“Our goal is to theoretically describe and explain thermodynamic properties of the frustrated magnetic systems obtained by experimental research. Good example is the well-known experimental fact of anomalous behavior of specific heat capacity, i.e. existence of multiple maxima in its temperature dependence,” explains Eva Jurčišinová. The Jurčišin couple managed to find direct connection between maximum number of these maxima in the behavior of the specific heat capacity and the parametric space of the model. “Based on these results we can theoretically explain not only why such multi-maxima structure occurs in the temperature dependence of specific heat capacity and what is its origin related to, but we also understand the reason why such maxima exists and therefore we can predict where and how many maxima will occur during measurement of the specific heat capacity.”

These findings can help with application use of the research. Frustrated magnetic materials react significantly to the presence of a magnetic field. “The already mentioned specific heat capacity may show significant changes when the magnetic field changes,” says Marián Jurčišin. Such phenomena is called the magnetocaloric effect and has a practical use, for example, in adiabatic (no heat exchange with the environment) (de)magnetizing cooling up to extremely low temperatures. Such cooling can become very effective alternative to conventional cooling. “Effectiveness of adiabatic cooling differs for various materials with different structures and can be achieved at different values of magnetic field,” he points out. “Our effort is to describe at which point we can expect the cooling to be the most effective, i.e. when will even small change of the magnetic field cause the largest change of the temperature of the system to the lowest possible temperatures.”

In addition, scientific couple tried to understand and explain how the fields of magnetic field values with the most efficient cooling can be moderated, from which initial states it is possible to reach the lowest temperature the fastest, and vice versa, which initial states do not lead to temperature reduction at all. What will be the use of such knowledge?

“Such theoretical research is important so that the material research can focus on finding the potential candidates which would achieve the highest efficiency at achievable magnetic field strengths, at room temperature of the initial state and, last but not least, whose production would be cost-effective and environmentally friendly,” explains Marián Jurčišin and his wife nods in agreement. The harmony is obvious. The married couple complement each other even in education. One is a studied physicist, second one is mathematician. And as they say in unison, their marital cooperation at work is not only very good, but also productive.

“We have to say that by being married we spend all the time together and therefore we can analyze and solve many problems ‘on the go’,” they smile and confirm that it is difficult for them to find a place, where they do not take their work with them, especially because they do not need large laboratories for their research. “Our work – research is our ubiquitous natural part.”

The couple consider the highest scientific award of the SAS as a huge satisfaction. “We really appreciate the price,” they both agree. “We also consider it as a huge encouragement to our future scientific work.” Are they not attracted by abroad? Institute of Experimental Physics SAS is the top, the home institute is excellent in its scientific world, is there no need to go “even higher”? “We had both worked abroad for longer time in the past, we worked at the Joint Institute for Nuclear Research in Dubna, Russian Federation, and we try to maintain our scientific contacts by short-term research stays. At the moment we are satisfied with the working conditions at the Department of Theoretical Physics at our institute, which we both consider to be as on one of the best in the structure of the SAS.” they add and one can hear the pride in the institute.

Original text: News at SAS (published on August 14, 2020)
Author of the original text: Andrea Nozdrovická
Photo: Katarína Čižmáriková, Katarína Gáliková