Condensed Matter Days 2009

List of invited talks

Generic behaviour of active transport in one dimension

Abhik Basu

Theoretical Condensed Matter Physics Division

Saha Institute of Nuclear Physics,

1/AF, Bidhannagar, Kolkata-700 064, India

Abstract:

Motivated by the phenomenologies of a variety of physical systems, e.g., the dynamics of molecular motors in eukaryotic cells and reaction-diffusion problems, we propose and analyse a class of one-dimensional stochastic lattice gas models, based on exclusion principles. Mean field theories and stochastic Monte Carlo simulations performed on these models yield density profiles with non-trivial spatial dependences including formation of localised and delocalised domain walls under various external conditions. Our results are indicative of the existence of a rich variety of macroscopic phases in relevant naturally occurring experimentally accessible systems.

Behavior in Wet Foam

Anushree Roy

Department of Physics & Meteorology

Indian Institute of Technology Kharagpur,

Kharagpur - 721302

Abstract:

Understanding the physics of wet foam mostly involves complicated mathematics along with critical experimentation. We find that even if one discards the complexities, some mysterious secrets in foam may be unearthed. In this talk, I will share our amusing experience while working with shaving foam.

Langmuir Blodgett Films of water soluble materials

Debajyoti Bhattacharjee

Department of Physics

Tripura University, (A Central University)

Suryamaninagar: 799130, Tripura

E.mail: debu_bhat@hotmail.com

Langmuir – Blodgett (LB) technique for the preparation of ultrathin films of various organic, metallorganic and polymeric compounds plays an increasingly important role as a means of organizing molecular materials at the microscopic level. The Langmuir – Blodgett (LB) technique has many potential applications in the field of molecular electronics, nonlinear optics, conducting thin films, Bio –membranes etc.

Among the several sophisticated thin film deposition techniques such as self-assembly, sol-gel processes etc., LB technique is one of the most versatile and convenient for designing ultra thin films. The technique permits the manipulation of materials at the molecular level and also enables the precise control of layer thickness, homogeneous deposition of the monolayer over large areas and the possibility to make multilayer structures with varying layer composition. Moreover, an additional advantage of the LB technique is that, monolayer can be deposited on almost any kind of solid substrate.

Ideal LB compatible materials are amphiphilic molecules with long alkyl chain as a tail part and a hydrophilic head group.

In recent time, several water soluble materials were also observed to form well organized Langmuir monolayer at the air water interface and were suitably deposited onto solid substrates to form mono- and multi – layered LB films. It was observed that certain water soluble cationic and anionic types of materials when interact with the amphiphilic molecules of a preformed Langmuir monolayer, adsorption of these molecules were occurred in the monolayer and subsequently a complex Langmuir monolayer was formed.

Characterizations of these films were done by AFM, In Situ FIM, FTIR, Fluorescence and UV-Vis spectroscopic technique.

In the first part of the talk, a short discussion on the Langmuir Blodgett film deposition technique will be presented.

In the second part, various experimental results will be discussed. Special emphasis will be placed on the fabrication of Organo – Clay hybrid LB films.

Microscopic properties to determine the universality class of stochastic sandpile models

Sitangshu Bikas Santra

Department of Physics,

Indian Institute of Technology Guwahati

Guwahati-781039, Assam, India

Abstract:

Classification of the universality class of different sandpile models are usually made by determining the values of the critical exponents related to the probability distributions of different macroscopic properties of an avalanche such as total number of toppling, total area, lifetime, etc. However, most of the information of an avalanche of a sandpile remains stored through a microscopic parameter, the toppling number of each sand column associated with individual lattice site like a spin variable s_i. In terms of the parameter s_i, a toppling surface can be defined. Multifractal analysis of toppling number correlation and toppling number density reviled a series of mutifractal dimensions for these measures. The analysis clearly classifies the universality class of different stochastic sandpile models such as Manna model, rotational sandpile model etc.

The Fundamental Features of the Colossal Magnetoresistive Manganese Oxides 
 

Govinda Chandra Rout

Condensed Matter Physics Group

P.G. Department of Applied Physics and Ballistics

Fakir Mohan University, Balasore, Orissa,- 756019

E-mail:profgcrout@gmail.com, Tel.No:09937981694 
 

Abstract:

      Large negative magnetoresistance(MR) is of current interest due to the possibility of producing devices which make use of this effect. This property can be tailored by making thin films consisting of various layers, but it is also found to occur naturally in doped manganite compounds. Colossal magnetoresistance(CMR) effect has been observed in doped manganites in understanding the electronic and magnetic properties of these materials. At low temperatures, properely doped manganites exhibit ferromagnetic metallic behaviour, while at high temperatures they exhibit a paramagnetic insulating behaviour. Though double exchange (DE) is clearly important for understanding the behaviour of the manganites, it is not enough. The kinetic energy depends sensitively on the behaviour of other spin and lattice degrees of freedom and in turn strongly influences their behaviour. The basic ingredients responsible for the exotic phenomena in manganites are the double exchange, charge ordering, orbital ordering and the different types of electron-phonon interactions like John-Teller effect, polaron and charge density wave effects. Nevertheless, it is difficult to identify the real controlling mechanism of each phenomenon. The challenge for theorist to construct, solve and interpret models which express this interplay. In the present communication we review the experimental observations and discuss a few model studies on manganites.

Charge ordering in manganites nanoparticles

Indranil Das

Saha Institute of Nuclear Physics, Experimental Condensed Matter Physics Division,

1/AF, Bidhannagar, Kolkata-700 064, India.

E-mail: indranil.das@saha.ac.in

Abstract

In this talk I will be discussing some of our novel findings in the field of Manganite nanoparticles. Charge ordering (CO) in the perovskite manganites has been a subject of intense research [1]. The novel interplay between spin, charge, orbital and phononic degree of freedom associated with this phenomenon is an intriguing problem of fundamental research. Beside this, large magnetoresistance and magnetocaloric effect can be obtained due to the magnetic field induced destabilization of charge ordered state, which is interesting from the application point of view. There are many studies regarding CO in the cases of polycrystalline and single crystalline bulk manganites. However little attention has been paid towards nanocrystalline form of the materials. The main objective of our study is to investigate the modification of charge ordering and related phenomena in manganites due to the reduction of particle size of the materials to the nanometer scale. A systematic detailed experimental study has been carried out in different manganites nanoparticles to investigate the effect of lowering of particle size on CO. We have observed the disappearance of charge order transition (COT) in the cases of nanocrystalline Pr_0.5Sr_0.5MnO₃ and Nd_0.5Sr_0.5MnO₃ [2-3]. However, COT is observed for Pr_0.65Ca_0.35MnO₃ nanoparticles of average particle size ~ 40 nm [4]. From Our studies, it appears that the martensitic-like character of COT is primary factor of the stabilization of charge ordered state (COS) in nanoparticles [3-4]. The co-existence of COS and ferromagnetic state can have strong influence on the magnetotransport and magnetocaloric properties of nanocrystalline Pr_0.65(Ca_1-ySr_y)_0.35MnO₃[5-9]. The systems exhibit large LFMR and magnetocaloric effect (MCE) due to destabilization of charge ordered state by magnetic field. For Pr_0.65(Ca_0.6Sr_0.4)_0.35MnO_3, the enhancement of magnetic refrigerant capacity occurs with the lowering of particle size and interesting table-like magnetocaloric effect has also been observed [9]. Our recent experimental observation indicates that the nanocrystalline La_0.125Ca_0.875MnO₃ exhibits inverse MCE due to the antiferromagnetic (AFM) transition [10]. The evidence of AFM transition in the cases of nanocrystalline manganites is in direct contradiction of existing experimental results for different manganite systems.

REFERENCES

1. Colossal Magnetoresistance, Ed. Y. Tokura (Gordon and Beach)

2. Anis Biswas, I. Das, C. Majumdar, J. Appl. Phys., 98 (2005) 124310

3. Anis Biswas, I. Das, J. Appl. Phys., 102 (2007) 064303

4. Anis Biswas, I. Das, Phys.Rev.B, 74 (2006) 172405

5. Anis Biswas, T. Samanta, S. Banerjee, I. Das, Appl.Phys.Lett.,92 (2008) 012502

6. Anis Biswas, I. Das, Appl.Phys.Lett.,91 (2007) 013107

7. Anis Biswas, T. samanta, I. Das, AIP.Conf.Proc.,1003 (2008) 109

8. Anis Biswas, T. Samanta, S. Banerjee, I. Das, Appl.Phys.Lett.,92 (2008) 212502

9. Anis Biswas, T. Samanta, S. Banerjee, I. Das, J.Appl.Phys.,103 (2008)

10. Anis Biswas, T. Samanta, S. Banerjee, I. Das, Appl.Phys.Lett.,94 (2009) 233109

Exchange bias effect and tunneling magnetoresistance in the hole doped cobaltites close to the percolation limit

S. Giri

Department of Solid State Physics, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032

Abstract

We observe the exchange bias effect in the mixed-valent cobaltites with perovskite structure. Exchange bias effect through the measurements of magnetoresistance is observed in the hole doped cobaltites close to the percolation threshold which is compared with the similar observation in the magnetic measurements. Exchange bias effect, tunneling magnetoresistance, time dependence of magnetoresistance have been interpreted by proposing a grain interior magnetic nanostructure of the compounds.

Summary of research activities related to condensed matter in the Dept. of Physics, JU

S. Tarafdar

Department of Physics,

Jadavpur University, Kolkata – 700 032

(Abstract not available)

Magnetic Superconductors and Borocarbides

Suresh G. Mishra

NISER

Bhubaneswar 751005

Abstract:

Conventional superconductors repell the magnetic flux from their interior, however, in certain materials superconductinvty can accomodate magnetic flux, the magnetic impurity, and even long range antiferromagnetic correlations. Magnetic superconductors are such materials. A brief historical perspective of magnetic superconductors will be presented in the light discovery of superconductivity in rare earth borocarbides in early nineties. There is a strong and intriguing interplay betweenmagnetic and superconductive correlations in these compounds too.

Superconductivity and magnetism in quaternary borocarbides: an experimental overview

Chandan Mazumdar

Experimental Condensed Matter Physics Division

Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064

The research on superconductivity in intermetallic compounds was in the wane ever since the discovery of high T_C superconductivity in oxide compounds in 1986. The limelight again came back to intermetallic compounds after the discovery of superconductivity in multiphase quaternary Y-Ni-B-C system (T_C~13K) at TIFR, Mumbai in 1993. The superconducting transition temperature (T_C) is quite high for intermetallic compounds that exhibit superconductivity, as most intermetallic compounds have T_C < 10K. A flurry of activities followed the discovery and enormous amount of work have been carried out worldwide. The single phase material had been identified as YNi₂B₂C (T_C~15.5K), which is a filled variant of the well-known tetragonal ThCr₂Si₂-type structure. The series of compounds, RNi₂B₂C (R = Y, rare earth) exhibit many interesting features: (i) coexistence and interplay of superconductivity and magnetism, as many members of this series exhibit both superconductivity as well as antiferromagnetic order where the Néel temperature (T_N) can even be higher that T_C, (ii) rich collection of magnetic structure in the magnetic members of this series, (iii) valence fluctuation behaviour in CeNi₂B₂C and heavy fermion behaviour in YbNi₂B₂C, (iv) possibility of having enhanced T_C (~23K) on the surface of YNi₂B₂C, (v) interesting flux line lattice and related effects, (vi) anisotropic gap despite s-wave superconductivity, (vii) reentrant superconductivity in HoNi₂B₂C, (viii) 4f-quadrupole ordering in TmNi₂B₂C, (ix) even higher T_C (~23K) in multiphasic Y-Pd-B-C system, (vi) very hard magnetic behaviour in multiphase Sm-Ru-B-C (H_C ~ 150 kOe at 5K), etc., to name a few. In this presentation, we will review the discovery and present an overview on the advances in the field of borocarbide compounds.