Biennial Report 2005-2007 - Saha Institute of Nuclear Physics

118 Biennial Report 2005-07Tp∼100 K in zero field cooledZFC magnetization, whereas field cooled magnetization continuouslyincreases down to 2 K. As long as the applied magnetic field is not large enough in comparisonwith the coercive field, a sharp decrease in ZFC magnetization is always observed below Tp. Thepeak temperature at Tp∼100 K is shifted to lower temperatures by applying sufficiently largemagnetic field. Ac susceptibility data also shows a sharp peak at 100 K, which is independentof frequencies 0.5 Hz-1 kHz of ac magnetic field amplitude 1 Oe. These observations, includingother measurements, suggest strong pinning effects in domain wall dynamics. We have noted thatelectrical behavior of the system is significantly affected by the magnetic ordering of the spins.Our results have shown the contribution of short range interactions above T C to the formation ofsmall polarons. The system shows colossal magneto resistance properties with a semiconductor tometallic transition below 80 K. A simple scaling law is used as a tool for the identification of shortrange magnetic interactions that may be difficult to determine using conventional magnetizationexperiments.RN Bhowmik, R RanganathanECMP4.1.1.29 Study of anomalous transport and thermal expansion behavior ofGdPd 3 B x C 1−xWe have studied the temperature variation of structural, magnetic and electrical-transport propertiesof GdPd3 and GdPd 3 B x C 1−x (x=0.25, 0.50, 0.75 and 1.00). These compound exist in ametallic pervoskite structure. One of the interesting aspects of this series of compounds is; one cantune the lattice parameter of the compounds, maintaining the crystal symmetry, by balancing thestoichiometry of the metalloids (boron and carbon) sitting at the body center position of cubic unitcell. By the variation of lattice parameter one gets profound changes in electrical transport andmagnetic properties of the compounds. GdPd3 and x=0.25 and 0.50 compounds exhibit positivevalue of temperature coefficient of resistance (TCR) and dominating antiferromagnetic type of ordering.On the other hand x=0.75 and 1.00 compounds exhibit negative TCR and canted magneticstructure. Our data also suggest that symmetry in site occupancy also plays an important rolein determining the electrical resistivity characteristics and structural properties, especially at lowtemperatures. The compounds with asymmetric distribution of boron and carbon (x=0.25 and0.75) exhibit sharp changes in TCR below T 45K, while the compounds with symmetric distribution(x=0.50 and 1.00) do not show such characteristics. GdPd 3 B 0.75 C 0.25 (x=0.75) monitors astructural transition below 45K while GdPd 3 B 0.25 C 0.75 (x=0.25) exhibits the rare phenomenon ofnegative thermal expansion. In contrast, GdPd 3 B 0.50 C 0.50 (x=0.50) and GdPd 3 B (x=1.00) do notshow such anomalies.Abhishek Pandey, Chandan Mazumdar, R Ranganathan, Molly De Raychaudhury†, Tanusri Saha-Dasgupta†, Saurabh Tripathi†, D Pandey†, Sushanta Dattagupta†ECMP4.1.1.30 Study of intermediate valence behavior in Ce 0.5 Eu 0.5 Pd 3 B xWe have performed structural, magnetic, electrical transport and Mössbauer spectroscopy studieson Ce 0.5 Eu 0.5 Pd 3 B x (x=0.0, 0.5 and 1.0). This compound contains two valence fluctuating ions,Ce and Eu, at the same lattice site (0, 0, 0) and thus one expects the interplay of different valencestates of these two ions may distort the crystal lattice and symmetries. However, our studies