SAHA INSTITUTE OF NUCLEAR PHYSICS
Department of Atomic Energy, Govt. of India
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Condensed matter Physics (Experiment)
Important Results:

i) Magnetism/Transport of magnetic and Superconducting oxide materials:

Magnetic, transport, thermoelectric power, and NMR measurements are being made in the newly discovered Fe-base superconductor RFeAsO (R = La, Ce, Pr, Nd, Sm, and Gd). Evidence of strong electron-phonon coupling was observed from normal and super conducting state transport properties of PrFeAsOF superconductor. The resistivity and 75As NMR results of superconducting CeFeAsO0.84F0.16 and its parent compound CeFeAsO reveal formation of vortex lattice in the superconducting state. Spin-fluctuation dominated ferromagnetically ordered state was revealed in Co based LaCoPO. Large low field magnetoresistance ([R(H)-R(0)]/R(0) ~ 100%) due to charge order melting was observed in nanocrystalline Pr0.65(Ca0.6Sr0.4)0.35MnO3 sample. This is in contrast to the general belief that charge order melting is a high field phenomenon. Field and pressure-induced magnetic phase transition in Sm0.52Sr0.48MnO3, pressure induced critical behavior of ferromagnetic phase transition in Sm-Nd-Srmanganites, electronic properties of LaxSr1-xCoO under pressure, size-induced metal insulator transition, glassy magnetic behaviour in La0.5Sr0.5CoO3 nanoparticles, orbital ordering in LaMnO3 spin polarised transport, charge ordering and related phenomena in magnetic nanostructures are some important findings in manganite/cobaltite system. Large magnetocaloric effect in Sm0.52Sr0.48MnO3, RMnO3 crystals, NdCeCuO6 superconductors was observed. Transport properties of Sr2FeMoO6 systems were also reported. Large Energy gap (230 K) in the excitation of Cu2+ electron spin in BaCu2V2O8 confirms alternating chain model. A small band gap of 25 K at the low energy excitation in SrNi2V2O8, (S=1 quasi-one-dimensional antiferromagnet) suggests its ground state as a disordered "spin liquid" Haldane state. A Core-shell model for AFM small particles have been proposed to discuss the increase of magnetization below AFM ordering ~ 20K for both in bulk and nano particles and unconventional relaxation of spinel oxide CoRh2O4 at 2K.

Covering the work of all faculties: C. Mazumdar, A. Poddar, B. Bandyopadhyay, I. Das, P. Mandal, S. Das, K. Ghoshray, R. Ranganathan and A. Ghoshray

ii) Magnetism and transport of intermetallic alloys

Transverse vibrations driven negative thermal expansion behaviour in GdPd3B0.25C0.75, an AFM anti-pervoskite material, magnetism of ordered metallic compound GdPd3BxC1-x, and the possibility of negative temperature coefficient of resistivity (NTCR) in the absence of chemical/ structural disorder have been studied. Valence fluctuation behaviour in filled/ vacant anti-perovskite compounds, intermediate valency of Eu stimulated by the valence instability of dopant Ce in cubic Ce0.5Eu0.5Pd3 and Ce0.5Eu0.5Pd3Bx have been reported. Magneto-resistance changes sign upon boron doping in TbPd3 and shows highest GMR ~30% in the series of RPd3 compounds. Novel method of generating magnetic phase diagram using magneto-caloric effect has been proposed. Evidence of Largest Magnetic Cooling Power was obtained from the Magnetocaloric Effect in Ho5Pd2. The evaluated value of relative cooling power (RCP) is 6.32 J/cm3 for a magnetic field change of 5 T. Interplay of RKKY, Kondo and crystal field interactions governs the fascinating ground state in RNi2Al5 (La, Ce and Pr). In the heavy fermion compound CePt2B2C, a suppression of the effect of magnetic correlation, due to the dominance of the Kondo effect over the RKKY interaction was observed. Microstructure, magnetic and Mossbauer studies on spark-plasma sintered (SPS) nano composite comprising Sm-Co-Fe (hard magnet) intermetallic phases and Fe(Co) (soft phase) suggest magnetically single phase behaviour of the SPS magnets. Structural and Magnetic studies on SPS SmCo5/Fe bulk nanocomposite magnet shows stronger exchange coupling between the hard and soft magnetic phases in SmCo5 with 5 wt % Fe than 10 wt % Fe containing sample.
 
Covering the work of all faculties: C. Mazumdar, B. Bandyopadhyay, I. Das, K. Ghoshray, R. Ranganathan and A. Ghoshray
 
iii) Microwave spectroscopy:

Conventional microwave spectroscopic studies of organic molecules like phenol and benzonitrile compounds in the gas phase reveals the ground state molecular constants and molecular structures. An indigenously built millimeterwave spectrometer was used to study the rotational spectra of DC discharge produced species like halogen cyanides (XCN, X= Cl, Br, I) and analysis leads to the assignment of many new transitions and determination of accurate rotational parameters and geometry of the molecules.

A.I. Jaman

iv) Non-linear transport in composites:

In case of field-dependent conduction in disordered systems, a sample with localised states is found to possess a field-scale. This observation leads to a phenomenological scaling, and to a nonlinearity exponent. The exponents in various systems are found to be integer multiples of a number ~0.08. 1/f-noise measurements reveal that bias exponents as well as noise levels may be good indicators of any changes in conduction mechanisms. The suggested model seamlessly fit the resistance minima data in composites. The higher temperature data are described by the Weibull distribution. An ultra low-noise current source has been developed.

C.D. Mukherjee and K.K. Bardhan

v) Ultrasonic related activity:

Study on the propagation characteristics of ultrasound through material medium has been done and a computational Fourier transform method for the characterization of materials has been proposed. Variations of ultrasound propagation parameters near structural phase transition in β-brass and simulation studies of some model systems have been reported.

B. Pal

 

Last Updated on Friday, 11 April 2014 19:25
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