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Abdel-Hafiez M.,Leibniz Institute for Solid State and Materials Research | Harnagea L.,Leibniz Institute for Solid State and Materials Research | Singh S.,Indian Institute of Science | Stockert U.,MPI for Chemical Physics of Solids | And 5 more authors.
Journal of Physics: Conference Series | Year: 2012

We present a calorimetric study on single crystals of Ca(Fe1-xCox)2As2 (x 0, 0.032, 0.051, 0.056, 0.063, and 0.146). The combined first order spin-density wave/structural transition occurs in the parent CaFe2As2 compound at 168 K and gradually shifts to lower temperature for low doping levels (x 0.032 and x 0.051). It is completely suppressed upon higher doping x ≥ 0.056. Simultaneously, superconductivity appears at lower temperature with a transition temperature around Tc ∼ 14.1 K for Ca(Fe0.937Co0.063)2As2. The phase diagram of Ca(Fe0.937Co0.063)2As2 has been derived and the upper critical field is found to be μ0H(c)2 11.5 T and μ0H(ab)c2 19.4 T for the c and ab directions, respectively. © Published under licence by IOP Publishing Ltd. Source


Duncan W.J.,Royal Holloway, University of London | Welzel O.P.,University of Cambridge | Moroni-Klementowicz D.,Royal Holloway, University of London | Albrecht C.,Royal Holloway, University of London | And 10 more authors.
Physica Status Solidi (B) Basic Research | Year: 2010

We examine the low temperature states of two transition metal compounds: (i) NbFe2 is poised on the threshold of ferromagnetism and can be pushed into a spin-aligned state at low temperature by modifying the composition slightly. Stoichiometric NbFe2 has been reported as a rare example of lowtemperature spin density wave order in a d-metal system. We have used pressure, field and composition tuning to examine the phase diagram of NbFe2. Near the quantum critical point, we find distinct non-Fermi liquid forms of the resistivity and heat capacity, whereas we observe strong, hysteretic magnetoresistance effects deep in the ordered phase. (ii) Ca3Ru2O7 undergoes first a magnetic transition (TN = 56 K) and then a structural transition (TS = 48 K) on cooling. Most of the Fermi surface is gapped out at low temperature, leading to a very low carrier density and small Fermi surface pockets. Pressure suppresses both TN and TS and, for p>3.5 GPa, induces a third low temperature state, which is robust up to at least 7.5 GPa. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Stockert U.,MPI for Chemical Physics of Solids | Pfau H.,MPI for Chemical Physics of Solids | Hartmann S.,MPI for Chemical Physics of Solids | Lausberg S.,MPI for Chemical Physics of Solids | And 7 more authors.
Physica Status Solidi (B) Basic Research | Year: 2013

We investigate the influence of small amounts of Ir and La substitution on the low-temperature thermal conductivity κ and thermopower S of YbRh2Si2. While the thermal conductivity is reduced in both cases due to the introduction of additional impurities, the effect on the thermopower is non-uniform: Ir substitution leads to a reduction of the absolute value of the thermopower. This is attributed largely to an enhanced disorder scattering. On the other hand, La substitution increases the absolute thermopower values. We discuss the possibility that this is due to band structure modifications upon doping into the Yb sublattice. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Stockert U.,MPI for Chemical Physics of Solids | Hartmann S.,MPI for Chemical Physics of Solids | Deppe M.,MPI for Chemical Physics of Solids | Caroca-Canales N.,MPI for Chemical Physics of Solids | And 3 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

We present measurements of the thermopower S(T) on CePd1-xRhx between 2 K and 300 K. For low Rh content, the system behaves as a ferromagnetic Kondo system with a Curie temperature TC of about 6 K, a Kondo scale smaller than TC, and an overall crystal electric field splitting of 210 K. As the Rh content increases TC is suppressed, while the average Kondo scale gets larger. Simultaneously, the presence of different Ce environments leads to a broad distribution of local Kondo scales ranging from very small values to above 50 K. As a consequence, large thermopower values are observed over an extended temperature range. Close to the critical concentration we find power-law dependencies of S/T vs T down to 2 K. For a Rh content of x=0.95 we may show explicitly that the thermopower contains contributions from Ce sites with different local energy scales. © 2015 American Physical Society. Source


Sarkar R.,MPI for Chemical Physics of Solids | Khuntia P.,MPI for Chemical Physics of Solids | Spehling J.,TU Dresden | Krellner C.,MPI for Chemical Physics of Solids | And 3 more authors.
Physica Status Solidi (B) Basic Research | Year: 2013

The ferromagnetic (FM) quantum critical system YbNi4P2 has been investigated by means of 31P-NMR. This is a newly discovered heavy fermion system which shows a FM transition at a very low TC=170mK. The present reported result is the extension of our previous work published in Ref. 11. 31P NMR results suggest the validity of the Korringa law in the presence of strong FM correlations. 31P NMR spectra have shown the anisotropic nature. The local magnetization derived from our NMR spectra is presented as a function of field at selected temperatures. The obtained spin-lattice relaxation rate 31(1/T1T) follows a weak power-law as T-0.75 in a wide field range down to T=1.8K. Possible scenarios for this unusual power-law behavior are discussed. Additionally, 31(1/T1T) is nicely scaled with the observed (C/T)2~T-0.8 power law in the temperature range 1.8-10K within the framework of renormalized Landau Fermi Liquid theory. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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