Papers by Srinivasan Ramakrishnan
c (0)∼ 2.7 K. When doped with Gd the T c (0) reduces and no superconductivity is observed above 1... more c (0)∼ 2.7 K. When doped with Gd the T c (0) reduces and no superconductivity is observed above 1.2 K with more than 15% (atomic) doping. The alloys, La 0.8 Gd 0.2 Rh 3 B 2 and La 0.6 Gd 0.4 Rh 3 B 2 show a jump at ∼ 70 K and rapid rise in magnetization below 10 K. However, no peaks are observed in at these temperatures in AC susceptibility which would have indicated magnetic ordering of the system. It is worth noting that GdRh 3 B 2 orders ferromagnetically at ∼ 93 K. We shall present results of our investigations, above 2 K, in magnetic and transport properties of polycrystalline specimens La x Gd 1−x Rh 3 B 2 (0 < x < 1). CeRh 3 B 2 is a ferromagnet with T c ∼ 115 K. The results of Gd doping in this reveal the survival of antiferromagnetic coupling between Ce and Gd spins.
Physical Review B, 1988
We report the lowand high-temperature resistivity studies of 315 compounds that have a low electr... more We report the lowand high-temperature resistivity studies of 315 compounds that have a low electron-phonon coupling constant (A,). The results do not agree with the model proposed by Gurvitch recently. We suggest further investigations before one starts using the universal plot of)I, vs p(0), where p(0) is the residual resistivity.
Physical Review B, 1999
Magnetic screening response of the superconductor 2H-NbSe 2 with varying pinning reveals a rich e... more Magnetic screening response of the superconductor 2H-NbSe 2 with varying pinning reveals a rich evolution of the peak effect from a history-independent sharp anomaly to a broad and strongly history dependent effect with internal structure. The results display a stepwise disordering of the vortex lattice through transformations affected by both thermal fluctuations and quenched disorder. ͓S0163-1829͑99͒03309-3͔ PHYSICAL REVIEW B
Superconductor Science and Technology, 2002
A comparison of the history effects in weakly pinned single crystals of a high T c YBa 2 Cu 3 O 7... more A comparison of the history effects in weakly pinned single crystals of a high T c YBa 2 Cu 3 O 7−δ (for H c) and a low T c Ca 3 Rh 4 Sn 13 , which show anomalous variations in critical current density J c (H) are presented via tracings of the minor magnetization hysteresis loops using a vibrating sample magnetometer. The sample histories focussed are, (i) the field cooled (FC), (ii) the zero field cooled (ZFC) and (iii) an isothermal reversal of field from the normal state. An understanding of the results in terms of the modulation in the plastic deformation of the elastic vortex solid and supercooling across order-disorder transition is sought. c < J rev c should hold. An elucidation of this fact via tracing of stable hysteresis loop above the PE region in weakly pinned crystals of 2H-NbSe 2 and CeRu 2 has been recently demonstrated [6,9].
Pramana, 2013
The feasibility study for searching neutrinoless double beta decay in 124 Sn using cryogenic bolo... more The feasibility study for searching neutrinoless double beta decay in 124 Sn using cryogenic bolometer has been initiated. For this purpose, a custom-built cryogen-free dilution refrigerator, having a large cooling power of 1.4 mW at 120 mK, has been installed at TIFR, India. This paper describes the design, installation and performance of a cryogen-free dilution refrigerator (CFDR-1200). The performance of CFDR-1200 has been analysed using Takano's model developed for conventional (wet) dilution refrigerators.
Journal of Physics: Conference Series, 2009
RCrSb3 crystallizes in a quasi two dimensional structure with RSb and CrSb2 layers stacked along ... more RCrSb3 crystallizes in a quasi two dimensional structure with RSb and CrSb2 layers stacked along a axis. This system displays rich magnetic structure due to complex magnetic interaction between 3d moments of Cr and 4f moments of rare earth ion. In this work, we present a comparative study on the heat capacity of R(La, Ce, Pr, Nd)CrSb3 which exemplifies the
Physical Review B, 2002
Compounds belonging to the R 2 Fe 3 Si 5 series exhibit unusual superconducting and magnetic prop... more Compounds belonging to the R 2 Fe 3 Si 5 series exhibit unusual superconducting and magnetic properties. Although a number of studies have been made on the first reentrant antiferromagnet superconductor Tm 2 Fe 3 Si 5 , the physical properties of Yb 2 Fe 3 Si 5 are largely unexplored. In this work, we attempt to provide a comprehensive study of bulk properties such as, resistivity, susceptibility and heat-capacity of a well characterized polycrystalline Yb 2 Fe 3 Si 5. Our measurements indicate that Yb 3+ moments order antiferromagnetically below 1.7 K. Moreover, the system behaves as a Kondo lattice with large Sommerfeld coefficient (γ) of 0.5 J/Yb mol K 2 at 0.3 K, which is well below T N. The absence of superconductivity in Yb 2 Fe 3 Si 5 down to 0.3 K at ambient pressure is attributed to the presence of the Kondo effect.
Physical Review Materials
We present the temperature dependence of the electrical resistivity, the magnetic susceptibility,... more We present the temperature dependence of the electrical resistivity, the magnetic susceptibility, and the specific heat of a high-quality single crystal of La 3 Co 4 Sn 13. As opposed to earlier reports on this system, these bulk properties exhibit clear anomalies at the phase transition at T * = 151(1) K, while the present data confirm the second-order character of this transition. X-ray diffraction with synchrotron radiation is used to solve the fourfold superstructure in space group I2 1 3 as it exists below T * in the charge-density-wave (CDW) state of La 3 Co 4 Sn 13. Unlike conventional CDW systems, we have observed hysteresis between the zero-field-cooled and field-cooled magnetization below the CDW transition. This discrepancy can be attributed to a possible magnetic instability arising out of correlations of Co in the lattice, developing at the CDW transition. The crystal structure shows that any modifications of the electronic state of Co might be due to modified binding characteristics of the Sn atoms comprising the trigonal prismatic coordination of Co, while the coordination of Co itself is hardly changed at the phase transition. The superconducting transition is observed at T sc = 2.85(2) K. The superconducting energy gap is estimated as 5 K on the basis of the specific heat measured down to 0.1 K. These results suggest that La 3 Co 4 Sn 13 is a conventional weak-electron-phonon-coupling superconductor.
Physical Review B
The first-order charge density wave (CDW) phase transition of Er 2 Ir 3 Si 5 is characterized by ... more The first-order charge density wave (CDW) phase transition of Er 2 Ir 3 Si 5 is characterized by a crystal structure analysis, and electrical resistivity, magnetic susceptibility and specific heat measurements. The incommensurate CDW is accompanied by a strong lattice distortion, from which it is shown that the CDW resides on zigzag chains of iridium atoms. The CDW transition affects the magnitude of the local magnetic moments on Er 3+ , implying strong coupling between CDW and magnetism. This could account for the observation that magnetic order is suppressed down to at least 0.1 K in the high-quality single crystal presently studied. Any disorder in the crystallinity, as in ceramic material, broadens and suppresses the CDW transition, while magnetic order appears at 2.1 K.
Healthcare Technology Letters
Cancer is one of the deadly diseases of human life. The patient may likely to survive if the dise... more Cancer is one of the deadly diseases of human life. The patient may likely to survive if the disease is diagnosed in its early stages. In this Letter, the authors propose a genetic search fuzzy rough (GSFR) feature selection algorithm, which is hybridised using the evolutionary sequential genetic search technique and fuzzy rough set to select features. The genetic operator's selection, crossover and mutation are applied to generate the subset of features from dataset. The generated subset is subjected to the evaluation with the modified dependency function of the fuzzy rough set using positive and boundary regions, which act as a fitness function. The generation and evaluation of the subset of features continue until the best subset is arrived at to develop the classification model. Selected features are applied to the different classifiers, from the classifiers fuzzyrough nearest neighbour (FRNN) classifier, which outperforms in terms of classification accuracy and computation time. Hence, the FRNN is applied for performance analysis of existing feature selection algorithms against the proposed GSFR feature selection algorithm. The result generated from the proposed GSFR feature selection algorithm proved to be precise when compared to other feature selection algorithms.
Solid State Communications
... 18,423(1976); Phys.Rev. B14, 4131 (1976). 6. PJ Webster, Contemp. Phys. 10, 559 (1969). 7. H.... more ... 18,423(1976); Phys.Rev. B14, 4131 (1976). 6. PJ Webster, Contemp. Phys. 10, 559 (1969). 7. H. Masumoto K. Watanabe, Trans. Japan Inst. Metals 17, 303 (1976). 8. J. Itoh, K. Shimizu, M. Mizutani, AK Grover, LC Gupta R. Vijayaraghavan,J. Phys. Soc. Japan 42, 1777 (1977). ...
Physical Review B
The peak effect in weakly pinned superconductors is accompanied by metastable vortex states. Each... more The peak effect in weakly pinned superconductors is accompanied by metastable vortex states. Each metastable vortex configuration is characterized by a different critical current density J c , which mainly depends on the past thermomagnetic history of the superconductor. A recent model [G. Ravikumar et al, Phys. Rev. B 61, R6479 (2000)] proposed to explain the 1 history dependent J c postulates a stable state of vortex lattice with a critical current density J st c , determined uniquely by the field and temperature. In this paper, we present evidence for the existence of the stable state of the vortex lattice in the peak effect region of 2H − N bSe 2. It is shown that this stable state can be reached from any metastable vortex state by cycling the applied field by a small amplitude. The minor magnetization loops obtained by repeated field cycling allow us to determine the pinning and "equilibrium" properties of the stable state of the vortex lattice at a given field and temperature unambiguously. The data imply the occurence of a first order phase transition from an ordered phase to a disordered vortex phase across the peak effect.
Physical Review B
We present a phenomenological model to describe features in the hysteretic magnetic response of w... more We present a phenomenological model to describe features in the hysteretic magnetic response of weak pinning superconductors across the peak effect region. It accounts for the experimentally observed history dependent behavior of critical current density and the metastability of the vortex state prior to and across the peak effect region of superconducting systems such as NbSe 2 , CeRu 2 , and YBa 2 Cu 3 O 7. Moreover, this model reduces to Bean's critical state model as a limiting case.
Physical Review B
We report on the observation of novel features in the minor hysteresis loops in a clean crystal o... more We report on the observation of novel features in the minor hysteresis loops in a clean crystal of N bSe2 which displays a peak effect. The observed behavior can be explained in terms of a supercooling of the disordered vortex phase while cooling the superconductor in a field. Also, the extent of spatial order in a flux line lattice formed in ascending fields is different from (and larger than) that in the descending fields below the peak position of the peak effect; this is attributed to unequal degree of annealing of the state induced by a change of field in the two cases.
Transactions of the IMF
ABSTRACT
Physica B: Condensed Matter
We have deposited thin films of CeRu2 onto SiO2/Si substrates by means of DC magnetron sputtering... more We have deposited thin films of CeRu2 onto SiO2/Si substrates by means of DC magnetron sputtering from a CeRu2 target. Resistivity data show a sharp superconducting transition at a maximum Tc of 5.2 K with a typical width of 0.2 K. The critical current in the superconducting mixed state jc shows high values at low fields, indicative of pinning of
Physica B: Condensed Matter
Physical Review B
We report the observation of a strongly coupled first-order charge-density wave ͑CDW͒ transition ... more We report the observation of a strongly coupled first-order charge-density wave ͑CDW͒ transition in a high-quality single crystal of the intermetallic compound Lu 5 Ir 4 Si 10. The first-order nature is ascertained by a very narrow and huge cusp ͑360 J/mol K͒ in the specific heat. The susceptibility and the resistivity also show sharp jumps at the transition T CDW ϭ83 K. The periodic lattice distortion associated with the CDW is exemplified by the formation of x-ray superlattice reflections along the tetragonal c ជ axis with q ជ Ϸ(0,0, 3 7) (T Ͻ83 K). Although our results are in accordance with a quasi-one-dimensional CDW scenario, the first-order transition suggests a strong interchain coupling. We propose Lu 5 Ir 4 Si 10 as a paradigm of such strong-coupling CDW systems. ͓S0163-1829͑99͒05808-7͔ PHYSICAL REVIEW B
Physica B: Condensed Matter
We report resistivity, DC susceptibility and heat-capacity studies on a single-crystal sample of ... more We report resistivity, DC susceptibility and heat-capacity studies on a single-crystal sample of Er Ir Si. Our studies indicate the presence of multiple transitions in this crystal as evidenced by resistivity and heat-capacity measurements. Resistivity studies show anomalies at 2.8, 55 and 145 K while the susceptibility exhibits a single maximum at 2.8 K due to antiferromagnetic ordering of Er moments. The heat-capacity data also display a sharp jump con"rming bulk magnetic ordering at 2.8 K.
Physical Review B, 1998
A study of path dependent effects in single crystals of CeRu2 and 2H − N bSe2 show that critical ... more A study of path dependent effects in single crystals of CeRu2 and 2H − N bSe2 show that critical current density Jc of the vortex state depends on its thermomagnetic history over a very large part of (H, T) parameter space. The path dependence in Jc is absent above the peak position (i.e., H > Hp) of the peak effect region, which we believe identifies the complete loss of order in the vortex structure. The highly disordered FC state can be healed into a relatively ordered vortex lattice by subjecting it to a large enough change in dc field (few tens of Oe) or by shaking the FC state with sufficient ac field (few Oe).
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Papers by Srinivasan Ramakrishnan