The Magnetic & Superconducting Materials Section at RRCAT has been
conducting research on various classes of magnetic materials and
superconductors including A15, heavy fermion and high temperature superconductors.
Our motivation for studying these materials is as follows:
Superconducting materials: The proper understanding of the properties of Abrikosov flux line
lattice (FLL) as a function of temperature (T) and magnetic field (H) is
crucial for tuning the dissipation-less current carrying capacity (JC)
of a type-II superconductor. By using the experimental facilities in our laboratory, we study the flux
line lattice of various classes of type-II superconductors namely high TC
materials, intermediate valence superconductor CeRu2, A-15 compound
V3Si, elemental Nb and V and transition metal alloys like Nb-Ti and
Mo-Re. A major emphasis has been to understand the local enhancement of JC
(H) near the upper critical field HC2 (T). Our research
activity has established that this local enhancement or peak in JC (H)
in many of these superconductors is associated with a first order phase
transition (FOPT) from one kind of FLL to another. This FOPT is marked by
distinct phase-coexistence and metastability.
We study superconducting materials for RF-superconducting cavity applications. We also investigate various superconducting materials processed differently,
with the idea to be able to find out what bestows the best superconducting
properties from the point of building accelerating cavities with highest
Magnetic materials: Magnetic materials are important (but somewhat hidden) component of
modern technology. Often fresh classes of magnetic materials are discovered
with new interesting functionality, which stimulates the growth of newer
technology. Three such classes of magnetic materials have emerged during
last two decades with much promise for immediate technological applications.
A brief description of these functional materials is given below.
- giant magnetoresistance and colossal magnetoresistance materials
- magnetocaloric materials and
- magnetic shape memory alloys.
Magnetoresistance, the change in electrical resistance with an applied magnetic field, is a useful tool in several areas of technology. For example, the computer hard drives use magnetoresistance to read the stored data. Most laptop computers now come fitted with high
capacity hard drives which use giant magnetoresistance (GMR) sensors as read head. In early 1990s a class of rare-earth manganese oxide materials (commonly termed as manganites) were found with colossal magnetoresistance (CMR). Manganites show exotic physical properties in the form of metal-insulator transition and varieties of magnetic, charge and orbital ordering dictated by strong electron-electron interaction and electron-lattice interaction, and provide a challenging area of research. A prospective picture for CMR effect in manganites is the formation of a percolation path involving the metallic ferromagnetic (FM) and insulating antiferromagnetic (AFM) phases across a FM-AFM transition region which can be manipulated by an applied magnetic field.
Originally measured in iron, the magnetic field induced temperature variation in a magnetic solid is known as "magnetocaloric effect"
(MCE). Instead of a working fluid undergoing a liquid-vapour transition in conventional refrigerator, a magnetic refrigerator can be envisioned using a magnetic solid, which heats up when magnetized and cools down when demagnetized. Such magnetic cooling has a potential to reduce global energy consumption and minimize the need of ozone depleting and greenhouse chemicals. The prospect of magnetic cooling as a viable alternative to vapour-compression technology has increased enormously since the recent discovery of giant MCE in various classes of rare earth-based magnetic materials.
Shape memory alloys (SMA) are metals that have the ability to remember a predetermined shape, and to return back to that
shape after being bent, stretched or otherwise mechanically deformed. This shape-memory effect is caused by a "thermoelastic martensitic transition" - a reversible transition between two different crystal microstructures in the concerned metallic system. SMAs have a wide range of technological applications including aeronautical, robotics and biomedical implants. A class of materials has now been discovered in late 1990s, which can undergo large reversible deformations in an applied magnetic field. These materials are now known as magnetic shape memory alloys (MSMA). Compared to the ordinary SMAs the magnetic control is easier to achieve and offers faster response in the MSMAs.
We have shown in recent years that a disorder-influenced first order magneto-structural phase transition provides the basic framework of
understanding the wide varieties of experimental results in these different classes of functional magnetic materials. This idea of generality has been developed on the basis of experimental works carried out in our group on various classes of magnetic materials namely, prototype giant magnetocaloric materials Gd5Ge4, doped-CeFe2 alloys showing GMR and MCE effects, and magnetic shape memory alloys NiCoAl, NiFeGa and NiMnIn. This generality is now extended to other classes of magnetic systems including CMR-manganites through the works of other research groups, both national and international. It should be mentioned here that the same first order phase transition is instrumental for enhancing the dissipation less current carrying capacity in many type-II superconductors (mentioned above), and for dictating the fundamental upper limit of the accelerating field in a superconducting RF-cavity.
We have discovered during our studies of various functional magnetic materials, that under certain circumstances the first order magneto-structural phase transition in many of these magnetic materials can be kinetically arrested giving rise to a highly non-equilibrium state whose dynamical properties are very similar to a structural glass. It is to be recalled here that the structural glasses are usually formed by cooling a viscous liquid fast enough through a first order liquid-solid phase transition. Although the structural glasses are known for centuries, a quantitative understanding of glass transition is still a major scientific challenge. This idea of a "magnetic glass" arising out of an arrested first order magneto-structural phase transition (introduced first by the researchers in our laboratory) has now started getting acceptance in the scientific community. Apart from various technological implications, such a "magnetic glass" with the relative ease of variation of temperature (T) and external magnetic field (H) will provide a robust platform to study the physics of glass in a two parameters H-T phase space. Such studies in two parameters phase space (e.g. temperature and pressure) of a structural-glass is not very easy because of the known experimental difficulty in dealing with the external pressure. The idea of such glassy phase is now being extended to other areas of ferroic materials like relaxor ferroelectrics.
The overall aim of the ongoing research in our group is to understand the interplay between the deeper scientific basis and the technological uses of magnetic materials and superconductors.
A new idea has emerged during the last decade to realize electronic devices which use electron spin instead of the charge and this has given rise
to an entirely new subject of spintronics. The crucial element in a proposed spintronics device is the spin-injector source, which will inject spin-polarized charge carriers in a seminconducting channel. Si being the most favoured material in semiconductor industry, gives an incentive to look for Si-based spin injector materials. An active research programme has been initiated in our group on transition metal monosilicides and Heusler alloys to look for potential spin-injector materials.
- SQUID magnetometer (MPMS 5, Quantum Design, USA): for dc magnetization measurements in the temperature range 1.8-400 K, and in the presence of magnetic fields up to 5.5 Tesla.
- Vibrating sample magnetometer (VSM, Quantum Design, USA): for dc magnetization measurements in the temperature range 2-300 K, and in the presence of magnetic fields up to 9 Tesla.
- 16 Tesla Cryo-magnet (Oxford Instruments, UK) with variable temperature insert (2K to 300K) for magneto-transport measurements.
- A recently commissioned cryostat magnet system with a magnetic field of 5T will be used as a standalone system for strain measurements as a function of temperature and magnetic field. The variable temperature insert to be used along with this magnet is under fabrication. An insert for magnetostriction and temperature dependent strain measurements is already operational with the 16T magnet system.
- Thermal properties (specific heat, thermal conductivity, thermoelectric power) measurements system (PPMS, Quantum Design, USA) in the temperature range 2-300 K and in the presence of magnetic fields up to 9 Tesla.
- Home made ac-susceptibility measurement system in temperature range down to 77K. This facility is now being extended to 4.2K using a new helium cryostat.
- Temperature dependent electrical conductivity measurements down to 77K using liquid nitrogen cryostat and down to 35K using a locally made closed cycle refrigerator.
- Home made Differential Scanning Calorimeter (DSC) working down to 77K.
- Argon arc furnace for synthesis of metallic alloys and intermetallic compounds.
- Microprocessor controlled high temperature (1500 C) box furnace.
- Inverted metallurgical microscope for observing microstructure of metallic samples.
- Access to thin-film preparation facilities- e-beam evaporation, ion-beam sputtering - in X-ray optics section of RRCAT.
List of publications
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People in the group.
List of people in the group (in alphabetical order)
Dr. Chaddah, P. (presently Director, UGC-DAE, CSR)
- Smt. Arora Parul
- Dr. Chandra L. S. Sharath (K. S. Krishnan research associate)
- Dr. Chattopadhyay, M. K.
- Mr. Chouhan, A.
- Dr. Khandelwal Ashish (K. S. Krishnan research associate)
- Mr. Manekar, M. A.
- Mr. Matin Md. (Phd. Student)
- Mr. Meena, R. K.
- Mr. Mondal P.
- Mr. Nath S.
- Dr. Roy, S. B. (Head, MAASD)
- Mr. Sharma, V. K.
- Dr. Sokhey, K. J. S.
Collaborators outside RRCAT.
- Prof. A. K. Nigam, TIFR, Mumbai.
- Prof. L. Cohen, Imperial College, London, UK.
- Prof. V. Pecharsky and Prof. K. Gschneidner Jr, Ames Lab., Iowa State University USA.
Some recent articles on magnetic materials.
Some recent articles on superconducting materials.
Sharath Chandra L. S., Chattopadhyay M.K.*, Sharma V.K.*, Roy S.B.*, Pandey S. K.
Temperature dependence of thermoelectric power and thermal conductivity in ferromagnetic shape memory alloy Ni50Mn34In16 in magnetic fields
Physical Review B, Vol. 81, p. 195105, May. 2010.
Sharma V.K.*, Chattopadhyay M.K.*, Roy S.B.*
Large magnetocaloric effect in Ni50Mn33.66Cr0.34In16 alloy
Journal of Physics D: Applied Physics, Vol. 43, p. 225001, May. 2010.
Roy S.B.*, Chattopadhyay M.K.*
Contrasting the magnetic response between a magnetic glass and a reentrant spin glass
Physical Review B, Vol. 79, p. 052407, 2009.
Chattopadhyay M.K.*, Arora P.*, Roy S.B.*
Magnetic properties of the field-induced ferromagnetic state in MnSi
Journal of Physics: Condensed Matter, Vol. 21, p. 296003, Jul. 2009.
Sharma V.K.*, Chattopadhyay M.K.*, Chouhan A.*, Roy S.B.*
Temperature and magnetic field induced strain in Ni50Mn34In16 alloy
Journal of Physics D: Applied Physics, Vol. 42, p. 185005, Sep. 2009.
Arora P.*, Chattopadhyay M.K.*, Roy S.B.*
Magnetic properties and large magnetocaloric effect of DyPt2
Journal of Applied Physics, Vol. 106, p. 093912, Nov. 2009.
Gupta P.*, Sokhey K.J.S.*, Rai S.*, Choudhary R.J., Phase D.M., Lodha G.S.*
Pulsed laser ablated off-stoichiometric thin films of the Heusler alloy Co2TiSn
on Si (100) substrate
Thin Solid Films, Vol. 517, p. 3650, 2009
Chattopadhyay M.K.*, Sharma V.K.*, Roy S.B.*
Thermomagnetic history dependence of magnetocaloric effect in Ni50Mn34In16
Applied Physics Letters, Vol. 92, p. 022503, 2008.
Chattopadhyay M.K.*, Roy S.B.*, Morrison K., Moore J. D. , Perkins G. K. , Cohen L. F. , Gschneidner jr. K. A., and Pecharsky V. K.
Visual evidence of the magnetic glass state and its re-crystallization in Gd5Ge4
Europhysics Letters, Vol. 83, p. 57006, 2008.
Manekar M.A.*, Roy S.B.*
Reproducible room temperature giant magnetocaloric effect in Fe-Rh
Journal of Physics D: Applied Physics, Vol. 41, p. 192004, 2008.
Sharma V.K.*, Chattopadhyay M.K.*, Roy S.B.*
Kinetic arrest of the first order austenite to martensite phase transition in Ni50Mn34In16: dc magnetization studies
Physical Review B: Condensed Matter, Vol. 76, p. 140401, 2007.
- Manekar M.A.*, Mukharjee C.*, Roy S.B.*
Imaging of time evolution of the first-order magneto-structural transition in Fe-Rh alloy using magnetic force microscopy
Europhysics Letters, Vol. 80, p. 17004, 2007.
Roy S.B.*, Myneni G. R., Sahni V.C.*
The influence of chemical treatments on the superconducting properties of technical niobium materials and their effect on the performance of superconducting radio frequency cavities
Superconductor Science and Technology, Vol. 22, p. 105014, Sep. 2009.
Mondal P.*, Manekar M.A.*, Srivastava A.K.*, Roy S.B.*
Bulk critical state and fundamental length scales of superconducting nanocrystalline Nb3Al in Nb-Al matrix
Physical Review B, Vol. 80, p. 024502, Jul. 2009.
Mondal P.*, Manekar M.A.*, Kumar R.*, Ganguli T.*, Roy S.B.*
Superconducting properties of nanocrystalline Nb3Al in Nb–Al matrix
Applied Physics Letters, Vol. 92, p. 052507, 2008.