1. 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.

2. 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.

3. 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.

Spintronics Materials: 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.

Experimental facilities

1. 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.
2. 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.
3. 16 Tesla Cryo-magnet with variable temperature insert (Oxford Instruments, UK) for physical properties measurements.
4. 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.
5. Home made ac-susceptibility measurement system in temperature range down to 77K. This facility is now extended to 4.2K using a new helium cryostat.
6. Temperature dependent electrical conductivity measurements down to 77K using liquid nitrogen cryostat and down to 35K using a locally made closed cycle refrigerator.
7. Home made Differential Scanning Calorimeter (DSC) working down to 77K.
8. Argon arc furnace for synthesis of metallic alloys and intermetallic compounds.
9. Microprocessor controlled high temperature (1500 C) box furnace.
10. Access to thin-film preparation facilities- e-beam evaporation, ion-beam sputtering - in X-ray optics section of RRCAT.

1. Dr. Chattopadhyay, M. K.
2. Mr. Chouhan, A.
3. Mr. Hareef Baba Shaeb, K (Ph. D. student)
4. Mr. Manekar, M. A.
5. Mr. Meena, R. K.
6. Dr. Roy, S. B. (Section head, M & SM section)
7. Miss. Sachdeva, P.
8. Mr. Sharma, V. K.
9. Dr. Sokhey, K. J. S.

1. Prof. A. K. Nigam, TIFR, Mumbai.
2. Prof. L. Cohen, Imperial College, London, UK.
3. Prof. V. Pecharsky and Prof. K. Gschneidner Jr, Ames Lab., Iowa State University USA.

• First order magneto-structural phase transition in various functional materials. S B Roy and P Chaddah Current Science 88 (2005) 71
  
• Experimental study of disorder-influenced first-order transitions in vortex matter and in magnetic systems S. B. Roy and P. Chaddah Phase Transitions 77 (2004) 767.
  

• Supercooling and giant relaxation of disordered vortex state in a doped CeRu₂ alloy
  M. K. Chattopadhyay, S. B. Roy and P. Chaddah
  Phys. Rev. B71 (2005) 024523.
  
• Possibility of Kauzmann points in the vortex matter phase diagram of single crystal YBa₂Cu₃O_7−δ
  S. B. Roy, Y. Radzyner, D. Giller, Y. Wolfus, A. Shaulov, P. Chaddah and Y. Yeshurun
  Physica C 390 (2003) 56
  
• Metastable vortex-states in YBa₂Cu₃O_7-x crystal
  
• Y.Radzyner, S.B.Roy, D.Giller, Y.Wolfus, A.Shaulov, P.Chaddah and Y.Yeshurun
  Phys. Rev. B61(2000) 14362.
  
• Peak effect in CeRu₂: History dependence and Supercooling
  S.B.Roy, P.Chaddah and Sujeet Chaudhary
  Phys. Rev. B62 (2000) 9191.
  

• Evidence of a magnetic glass state in the magnetocaloric material Gd₅Ge₄
  S. B. Roy, M. K. Chattopadhyay, P. Chaddah, J. D. Moore, G. K. Perkins, L. F. Cohen, K. A. Gschneidner, Jr., and V. K. PecharskyPhys. Rev. B74, (2006) 012403
  
• Training effects in Gd₅Ge₄:Role of microstructure
  Meghmalhar Manekar, M. K. Chattopadhyay, R. Kaul, V. K. Pecharsky and K. A. Gschneidner, Jr.
  J. Phys.: Condens.Matter 18 (2006) 6017
  
• Magnetocaloric effect in CeFe₂ and Ru-doped CeFe₂ alloys.
  M. K. Chattopadhyay, M. A. Manekar and S. B. Roy
  J. Phys. D: Appl. Phys 39 (2006) 1006
  
• Kinetic arrest of the first-order ferromagnetic-to-antiferromagnetic transition in Ce(Fe_0.96Ru_0.04)₂: Formation of a magnetic glass.
  M. K. Chattopadhyay, S. B. Roy and P. Chaddah
  Phys. Rev. B72 (2005) 180401
  
• Magnetic and martensitic transitions in Ni-Fe-Ga alloy
  S. Majumdar, V.K. Sharma, M. Manekar, Rakesh Kaul, K.J.S. Sokhey, S.B. Roy and P. Chaddah
  Solid State Commun. 136 (2005) 85
  
• Metastable magnetic response across the antiferromagnetic to ferromagnetic transition in Gd₅Ge₄
  M. K. Chattopadhyay, M. A. Manekar, A. O. Pecharsky, V. K. Pecharsky, K.A. Gschneidner Jr., J. Moore, G. K. Perkins, Y. V. Bugoslavsky, S. B. Roy, P.Chaddah and L. F. Cohen
  Phys. Rev. B70 (2004) 214421.
  
• First order magnetic transition in doped CeFe₂ alloys: Phase coexistence and metastability
  S. B. Roy, G. K. Perkins, M. K. Chattopadhyay, A. K. Nigam, K. J. S. Sokhey, P. Chaddah, A. D. Caplin and L. F. Cohen
  Phys. Rev. Lett. 92 (2004) 147203.
  
• Signatures of phase separation across the disorder broadened first order ferromagnetic to antiferromagnetic transition in doped-CeFe₂ alloys
  K. J. S. Sokhey, M. K. Chattopadhyay, A. K. Nigam, S. B. Roy and P. Chaddah
  Solid State Commun. 129 (2004) 19.
  
• Metastability and giant relaxation across the ferromagnetic to antiferromagnetic transition in Ce(Fe_0.96Ru_0.04)₂
  M. K. Chattopadhyay, S. B. Roy, A. K. Nigam, K. J. S. Sokhey and P. Chaddah
  Phys. Rev. B68 (2003) 174404.
  
• First order transition from ferromagnetism to antiferromagnetism in Ce(Fe_0.96Al_0.04)₂ : a magnetotransport study
  Kanwal Jeet Singh, Sujeet Chaudhary, M. K. Chattopadhyay, M. A. Manekar, S.B. Roy and P. Chaddah
  Phys. Rev. B65 (2002) 094419.
  
• First order transition from antiferromagnetism to ferromagnetism in Ce(Fe_0.96Al_0.04)₂
  M. A. Manekar, Sujeet Chaudhary, M. K. Chattopadhyay, K. J. Singh, S. B. Roy and P. Chaddah
  Phys. Rev. B64 (2001) 104416
  
  

• Transport properties of ferromagnetic Heusler alloy Co₂TiSn
  S. Majumdar, M. K. Chattopadhyay, V. K. Sharma, K. J. S. Sokhey, S. B. Roy, and P. Chaddah
  Phys. Rev. B72 (2005) 012417.
  
• Spin polarisation and anomalous Hall effect in NiMnSb films
  W.R. Branford, S.B. Roy, S.K. Clowes, Y. Miyoshi, Y.V. Bugoslavsky, S. Gardelis, J. Giapintzakis, L.F. Cohen
  J. Mag. Mag. Mat. 272-276, suppl. 1 (2004) E-1399.
  
• Magnetic response of Fe_1-xCo_xSi alloys: A detailed study of magnetization and magnetoresistance.
  M. K. Chattopadhyay, S. B. Roy, Sujeet Chaudhary, Kanwal Jeet Singh and A. K. Nigam
  Phys. Rev B66 (2002) 174421.
  
• Magnetic properties of Fe_1-xCo_xSi.
  M. K. Chattopadhyay, S. B. Roy, and Sujeet Chaudhary
  Phys. Rev. B65 (2002) 132409