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Projects / Programmes source: ARIS

Exchange interactions in selenides and tellurides – key for new functional low-dimensional magnetic systems

Research activity

Code Science Field Subfield
1.02.01  Natural sciences and mathematics  Physics  Physics of condesed matter 

Code Science Field
P260  Natural sciences and mathematics  Condensed matter: electronic structure, electrical, magnetic and optical properties, supraconductors, magnetic resonance, relaxation, spectroscopy 

Code Science Field
1.03  Natural Sciences  Physical sciences 
Keywords
exchange interactions, low-dimensional systems, lone pair electrons, neutron scattering, selenides, tellurides
Evaluation (rules)
source: COBISS
Researchers (1)
no. Code Name and surname Research area Role Period No. of publicationsNo. of publications
1.  26465  PhD Matej Pregelj  Physics  Head  2013 - 2015  130 
Organisations (1)
no. Code Research organisation City Registration number No. of publicationsNo. of publications
1.  0106  Jožef Stefan Institute  Ljubljana  5051606000  90,038 
Abstract
The beauty of low-dimensional (low-D) magnetic systems lies within their amazing duality. Even though their topology is very simple, they exhibit a wealth of fascinating magnetic ground states (spin-liquids, spin-glasses, incommensurate spiral states, etc.), and exotic excitations (spinons, amplitudons, phasons, etc.). This occurs due to pronounced quantum fluctuations, which damp magnetic correlations and thus oppose the establishment of long range order, favored by magnetic anisotropies or interactions along the third dimension. Low-D magnetic systems are hence highly susceptible to small perturbations, allowing the interplay between different degrees of freedom, leading to quantum critical points, Luttinger liquid phases, magnetoelectric or anisotropic thermal response – phenomena, which are attractive both from theoretical as well as technological aspects. Moreover, their simplicity allows that the observed response can often be explained by exact analytical or high-precision numerical calculations making low-D magnetic systems one of the hottest topics in condensed matter physics. The recent breakthrough was the realization that low-D magnetic systems are not limited to copper-oxides, as diverse low-D magnetic lattices were found also in family of selenides and tellurides. The key feature of these systems is that they involve stereochemically active catinos with lone-pair electrons (LPE), e.g., Se4+ and Te4+, which reduce the number of chemical bonds and can thus lower the dimensionality of the magnetic lattice. Moreover, in these compounds magnetic interactions can be mediated by M-O-T-O-M (M is transition metal, T is Te4+ or Se4+) bridges, i.e., placing the stereochemically active LPE within the exchange pathway. As a result, intriguing effects like magnetoelectric coupling or unconventional thermal conductivity might occur. However, in contrast to “simple” magnetic oxides, where exchange interactions can be estimated from the crystal structure by Goodenough-Kanamori rules, the exchange nature of Te4+/Se4+ mediated pathways is still a puzzle, as it demands individual experimental and theoretical treatment.   The prime objective of our project is to derive exchange rules for Te4+/Se4+ mediated pathways and thus to enable a faster route to new functional low-D materials. In parallel, we will explore exotic ground states and possible ways to influence them, search for unconventional excitations and pursuit new functionalities of low-D Te4+/Se4+ systems.   We plan to employ a broad range of experimental (neutron and x-ray scattering, magnetic resonance) and theoretical (mean field theory as well as Holstein-Primakov calculations) tools to study a number of low-D Te4+/Se4+ compounds that vary in the exchange topology (cluster, 1D, 2D), in the exchange bridging lone-pair cation (Te4+, Se4+) as well as in spin (1/2, 1, 5/2). This will give us a comprehensive overview of the selenides/tellurides’ behavior, an insight to the specific effects of different degrees of freedom, and eventually enable us to meet the intended objectives.   Beside the scientific goals, the project is aimed to set foundations of magnetic neutron scattering research at Jožef Stefan Institute, Ljubljana, Slovenia, in line with ongoing efforts to join Central European Neutron Initiative. It will also develop collaborations with leading research groups over the world and improve the participation of Slovenia in large-scale research facilities.
Significance for science
Transition metal selenides and tellurides are extraordinary classes of materials, which exhibit numerous intriguing crystal structures that vary in the dimensionality of the magnetic exchange network - from the simplest, cluster-like, arrangements to complex networks of interacting 1D or 2D entities. Moreover, these two families of compounds appear to offer countless possibilities to generate new structures with complex, potentially low-D, arrangements of magnetic ions. However, in spite of their amazing properties, Te4+/Se4+ based low-D systems are still far from being used for broad applications, as they demand comprehensive individual treatment, employing several complementary experimental techniques as well as complex theoretical calculations, which represent a huge time loss in the process of developing/designing new low-D magnetic materials with desired functionalities. The general rules for magnetic exchange of Te4+/Se4+ pathways, which were developed in course of our project, hold a promise for a scientific and potential technological breakthrough in the design of novel materials with specific characteristics; e.g., anisotropic heat transport, magnetoelectric coupling, etc.. Our results clearly show that exchange interactions of the M-O-Te/Se-O-M type, where interatomic distances along the path are smaller than two Angstroms, typically reach the strength of several tens of Kelvins and are antiferromagnetic regardless of the angles along the exchange path. Based on the derived rules it should be possible to obtain an estimate of the exchange network in the system already from structural information and basic “laboratory” measurements (magnetic susceptibility and specific heat), thus avoiding a number of time-consuming experimental and computational tasks. At last, we point out the amazing discovery of a broadband microwave absorption in the mixed phase of metamagnet. The absorption extends over ten decades in frequency and occurs at exactly determined magnetic field. This allows for precise control (on/off) of the absorption, which makes these materials highly interesting for application in microwave filtering devices.
Significance for the country
Besides the scientific advances, our project lead to new collaborations (and strengthen old ones) with leading research groups across the world (USA, Europe, and Japan), improve the participation of Slovenian research groups at large-scale European facilities, and stimulate the integration of Slovenia into magnetic neutron scattering community, which started with postdoctoral training of Matej Pregelj at Laboratory for Neutron Scattering at Paul Scherrer Institutu, Switzerland. This is a very important step, since Slovenia is not yet a member of international neutron communities, hence establishment of new relations and regular collaboration with foreign experts is of the essence. Finally, more than a few studies that were produced during the project were published in important international journals and presented at international conferences, what proves that Slovenia not just keeps the pace with the most developed countries in the world but also show trends at the highest level.
Most important scientific results Annual report 2013, 2014, final report, complete report on dLib.si
Most important socioeconomically and culturally relevant results Annual report 2013, 2014, final report, complete report on dLib.si
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