Research

RESEARCH  PROJECTS :


DETAILS  OF  RESEARCH  WORK :

Ø    During Ph.D:

 Topic of research:

 Magnetic field dependent transport properties of perovskite oxides of colossal magneto-resistive materials.

 ·         Systems Studied:

     a. LaMnO3+d

     b. La1-xPbxMnO3 (0.0 < x < 0.5)

     c. La0.5Pb0.5MnO3 (With three different grain size)

     d. La0.5Pb0.5Mn1-yCryO3 (0.0 < y < 0.45)

 ·         Characterization:

     a.  X-Ray Diffraction.

     b. Temperature variation of resistivity under magnetic field.

    c. Magnetic field dependent temperature variation of thermoelectric power 

    d. Thermal variation of Hall Coefficient in different magnetic field.

    e. Defect induced (by heavy ion beam irradiation) study.

 ·    Instrumental setup made:

    a.  Thermoelectric power setup used for characterization as mentioned above.

    b.  Hall effect setup used for characterization as mentioned above.

·         Main Results:

My thesis work deals with the measurement and analysis of magnetic field dependent resistivity and thermoelectric power. I’ve also measured the thermal variation of Hall coefficient of several CMR samples. From the resistivity data

Ø       We have found for the first time that the high temperature semiconducting regime (above metal-insulator transition temperature Tp) of the resistivity data can be divided into two distinct regions. The higher part (above qD/2) is well fitted with Small Polaron Hopping (SPH) model, but the region between Tp and qD/2 was found to be dominated by Variable Range Hopping (VRH) mechanism.

Ø       Appearance of semiconductor to metal transition is accompanied by a change from non-adiabatic to adiabatic hopping conduction.

Ø       A change from non-adiabatic (for T>qD/2) to adiabatic (for T<qD/2) hopping conduction mechanism takes place in LaMnO3, showing no metal-insulator transition.

Ø       It is observed that, above Tp, the temperature range for SPH increases and VRH decreases with increasing grain size.

Ø       Electron magnon scattering dominates the low temperature metallic region.

 Thermal variation of Magnetic field dependent thermoelectric power data shows interesting results.

Ø     Like resistivity, signature of electron-magnon scattering has also been confirmed form low temperature thermopower analysis.

Ø     The high temperature region was found to be dominated by SPH mechanism.

Ø     No signature of VRH model is obtained form the thermopower data, since thermopower between grain to grain is additive in nature.

Ø     Thermoelectric power is less sensitive to grain size.

Ø     It was found that polaronic radius increases with magnetic field.

 Very few works have been done on the Hall coefficient measurements on CMR materials. From our measurements

Ø     We have found that the high temperature regime is dominated by SPH model, with activation energy is 2/3 of that obtained from resistivity data, which confirmed that adiabatic SPH model controls the high temperature regime.

Ø     The high temperature Hall coefficient was found to be negative, which confirms that the charge carriers in this region is electronic polaron.

Ø     Thermal variation of Hall mobility also shows interesting behavior.

 

 Ø    After Ph.D:

 ·       Indira Gandhi Center for Atomic Research, Kalpakkam, India:

             Topic of research:

   Structural, micro-structural characterization and thermophysical property studies of some materials related to fast reactor.

·         Characterization:

a.       High temperature X-Ray Diffraction.

b.       Tunneling electron microscopy (TEM).

c.       Scanning electron microscope (SEM).

d.       Energy dispersive X-Ray spectroscopy (EDX).

e.       Electron Microprobe Analysis (EPMA).

f.        High temperature calorimetry.

·     Laboratoire Photons Et Matière, UPR 5 –CNRS, E.S.P.C.I, Paris, France :

        Topic of research:

           Study of magneto-transport property (down to 100 mK and upto 12T magnetic field) of BixSb1-x family of systems, which are host to high-mobility Dirac electrons with interesting thermoelectric behaviour. Intensively involved in the study of the Nernst response across the quantum limit in this family

      ·     Department of Physics, University of Calcutta, Kolkata, India:                              

        Topic of research:

      Presently, my interest is to work on bewildering variety of transport and other physical phenomena observed in strongly correlated electron systems. At University of Calcutta, I’m now involved in the following research areas of Materials Science:

            ·         Characterization:                 

                  a.       Room temperature X-Ray Diffraction for phase identification and structural analysis. 

                 b.       Low temperature transport property (resistivity, thermopower etc.) measurement down to 10 K, using closed cycle cryostat.

                c.       Magneto-transport viz., magnetoresistance, Hall effect etc. study (in collaboration).

               d.       Magnetic measurement using SQUID VSM magnetometer.