Investigation of superconducting and multiferroic materials

Project leaders

Massimiliano Polichetti, Krastyo Buchkov

Agreement

BULGARIA - BAS - Bulgarian Academy of Sciences

Call

CNR/BAS triennio 2019-2021 2019-2021

Department

Physical sciences and technologies of matter

Thematic area

Physical sciences and technologies of matter

Status of the project

New

Research proposal

The topics of the present project-proposal are focused on novel trends in materials science: preparation and investigation of perspective superconducting, multiferroic and 2D materials (in various structural forms: crystals, nanostructures and monolayers).
The research program of the project-proposal proposes a continuation and expansion of our joint research activities. Our work was dedicated to investigations of mixed state and magnetic properties of iron-based superconductors (IBS) [1-3] and multiferroic systems. We would like to continue our work on these topics but also to develop our collaboration in new directions to study multiferroic nanostructures and 2D materials.

We propose the following research directions:

(1) Iron chalcogenide superconductors as part of the major family of Iron based superconductors have attracted major scientific interest. They have the simplest crystal structure among the iron-based superconductors (IBS), and possess the lowest anisotropy values, high upper critical fields and high critical current densities. Therefore, these materials are considered as reference materials for exploration of the properties of all layered Fe based superconductors, both to advance fundamental physics as well as for perspectives for high power applications.
Basing on these facts, also in the frame of a previous IT-BG bilateral project, in the last years we have studied intensively the properties of flux grown FeSe crystals and Bridgman grown FeSeTe single crystals. By means of various structural, electro-transport and AC/DC magnetization experimental techniques, we have investigated in details their basic critical parameters, current density, strong pinning characteristics and vortex state transition effects as 'second magnetisation peak' which are among the most important study topics.
Nevertheless there are so many open questions regarding the mixed state properties (vortex dynamics) and the sophisticated correlations with their structure and morphology. In addition we would like to analyse in details these unexplored topics by means of the AC magnetic susceptibility analysis. This is one of the prime experimental techniques used for the investigations. In particular we intend to deeply analyse the AC field amplitude and frequency variation effects on the vortex dynamics processes and vortex pinning energy by using an innovative experimental approach based on the full set of experimental dependencies of the AC magnetic susceptibility harmonics - XAC (f, HAC, T = const)-, which are rarely investigated and, to our knowledge, are not applied to iron based superconductors so far.



(2) The Multiferroic materials are also a topic of significant interest due to the combined and diverse electric and magnetic nature, so resulting attractive in both fundamental and practical points of view in the fields, as examples, of spintronics and vortextronics

We are particularly interested in investigation of nanostructures based on the perspective multiferroic compound La0.7Sr0.3MnO3: Si (LSMO/Si), deposited directly on Si substrate, the basic material of modern electronics. We would like to investigate so far unexplored possibilities of their combined properties. The thin film structures will be deposited by means of RF single magnetron sputtering. We plan to explore the options of optimal deposition routine, how the fabrication process influences the structure, and how it is possible the engineering of the nanostructures. We will aim in the creation of structures in 50nm. The thin films will be structurally characterized and their magnetic and magnetoelectric properties will be analysed in high magnetic fields (up to 9T) and wide temperature ranges 2-400K. The main emphasis of the studies will be on linear and non-linear AC magnetic response (by means of ACMS) of the nanostructures and more precisely for acquiring info about the spin and magnetic domain wall dynamics. In addition we will study their magneto-optical response.

As a secondary task we intend also to make a comparative measurements on other multiferroic compounds (in form of single crystal) from the ReMnO3 family.



(3) Two Dimensional transition metal dichalcogenides

In the framework of this collaboration project, we will also explore new possibilities and gain experience in some novel directions. The development of 2D structures is one of the emerging and rapidly expanding research topics due to diverse optical, electronic (spin and orbital) and transport properties. Particularly challenging are the synthesis and investigation of monolayer transition metal dichalcogenides (for instance MX2 - M = Mo, W, Nb and X = Se, S, Te). We will start series of preliminary studies of their rarely explored magnetic and magneto-optical properties. The new challenges for the team will be particularly the preparation and consequent modification of the 2D structures (by means of chemical vapour deposition technique) and magneto and magneto-optical characterisation.

It is worth underlying that the contacts between the Italian and the Bulgarian groups started in 2011 and continued within our first inter-academic project (2013-2015). In the collaboration, the Bulgarian side has benefited from the expertise of the Italian colleagues in the analysis of complex properties of superconducting and multiferroic materials, and for making possible some experimental investigations. On the other hand, Italian side also has benefited from the high quality samples (crystals and nanostructures) provided, and from the assistance for the educational process of young scientists.
The scientific results of our joint research activity are systematized and published in 6 articles in journals of middle-high impact factors and in 1 book chapter.
In order to be able to continue effectively the collaboration, it needs to be supported by periodic visits and stays of the researchers, involved in the project, to the partners' laboratories/structures.

Research goals

Young scientists and students will be also involved in the research projects and will be supervised and consulted by experienced and esteemed scientists. The main priority of the project will be the gain of scientific experience. Moreover this project will provide the best opportunity for the continuation and the improvement of the scientific partnership, and a solid basis for long-term cooperation and possible joint applications for future scientific projects, for instance, in the frame of the Horizon 2020 program.
All project participants will be involved in the planned activities for the development and the improvement of multidisciplinary skills.
The results will be useful in scientific terms and for the development of new perspective materials and more efficient producing technologies. In addition, the results will be presented in common articles and international conferences.
Among the main goals to reach, we underline:
1) the understanding of the dependence of vortex dynamics processes and pinning energy in the analysed Iron based superconductors, on the ac field amplitude and frequency of the applied AC magnetic field
2a) the optimisation of the deposition routines of LSMO/Si nanostructured thin films, and the study of their magnetic and magnetoelectric properties.
2b) the comparison of the mproperties of multiferroic samples from the ReMnO3 family
3) the preparation of 2D structures of transition metal dichalcogenides

Last update: 19/04/2024