Research Projects

Rationale of the research: Mineral francisite, particularly Cu₃Bi(SeO₃)₂O₂Cl (CBSC) is really a fascinating compound. It possesses an antiferromagnetic (AFM) transition (35K) and a structural antiferroelectric (AFE) transition (115K). The AFM state is highly fragile due to presence of strong ferromagnetic (FM) intralayer exchange. The AFM state can be reverted to FM state by applying a critical magnetic field and is termed metamagnetic (MMT) transition. Now when any rare earth (RE) replaces Bi due to 3d-4f interaction, spin reorientation transition (SRT) occurs. In this project we are proposing to study suitable RE (Nd, Sm and Dy) doped (in nominal and heavy proportion) doped (at Bi site) CBSC [Cu₃[RExBi₁1-x](SeO₃)₂O₂Cl (CRBSC)] and transition metal (TM) (Co,Ni) co-doped (at Cu site) [(Cu1-yTMy)₃[RExBi1-x](SeO₃)₂O₂Cl (CTRBSC)] so that all structural (AFE) and magnetic (AFM, MMT and SRT) transitions are observed in a single compound and in an enhanced magnitude. Scientific Objectives: Study of structural AFE transition, magnetic field induced metamagnetic and spin reorientation transitions and magnetoelectric (ME) and magnetodielctric (MDE) coupling in CBSC, CRBSC, and CTRBSC. Model to be tested: The interplay of all structural and enhanced magnetic transitions to be tested in this project. The discovery of antipolar soft phonon mode driven AFE transition [PRL, 124, 97603] opens a huge playground to verify elementary theories of AFE materials. Experiments to be carried out: Proposed compounds will be prepared in the laboratory by modified Solid State reaction method using the Carbolite furnace (to be procured from the grant of this project). Structural analysis will be done using laboratory based and temperature dependent Synchrotron based X-ray diffraction and low temperature Raman spectroscopy. Temperature dependent Neutron Diffraction measurement will be required for structure as well as magnetic structure. Field (0-7T) and temperature (2-400K) dependent dc and ac magnetization measurement will be performed using SQUID VSM. ME, MDE coupling measurement will be using high magnetic field system [ resistivity and dielectric and magneto-dielectric measurement facility]. The nature of doping (substitutional or interstitial) will be investigated using X-ray absorption Fine Structure, particularly extended X-ray absorption Fine structure (EXAFS) spectroscopy measurement. Significance to the field of research: The study of all possible doping induced enhanced magnetic (AFM, MMT, SRT) and AFE structural transitions and their interplay is very interesting. ME, MDE coupling study might be fruitful from the perspective of a new class of potential multiferroic materials. Another probable electric field induced AFE to ferroelectric (FE) transition (as FE state is slightly higher in energy with respect to AFE state) like magnetic field induced MMT transition would really be interesting if detected.

Antiferroelecric compound, Antiferromagnetic material, Metamagnetic transition, Spin reorientation transition, Magnetodielectricity, Structural transition.