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[en] The low-temperature magnetic phase transition in LuFe2Ge2 is thought to be associated with itinerant magnetism. The effects of Y and Sc substitutions on the Lu site, as well as Ru and Co substitutions on the Fe site, on the low-temperature magnetic phase transition of the LuFe2Ge2 compound have been studied in single crystals via microscopic, thermodynamic and transport measurements. On one hand, Co substitution suppresses the transition below our base temperature of 2 K even at our lowest substitution level. On the other hand, Sc substitution enhances the transition temperature, and Y or Ru substitution suppresses the transition to lower temperature. Phase diagrams for Y, Sc and Ru substitutions have been constructed and the possibility of a unifying, composite diagram is discussed.
[en] Highlights: • Over the past 14 years MgB_2 has gone from a startling discovery to a promising, applied superconductor. • In this article we present a brief overview of the synthesis and the basic superconducting properties of this remarkable compound. • In particular, the effects of pressure, substitutions and neutron irradiation on superconducting properties are discussed. - Abstract: Over the past 14 years MgB_2 has gone from a startling discovery to a promising, applied superconductor. In this article we present a brief overview of the synthesis and the basic superconducting properties of this remarkable compound. In particular, the effect of pressure, substitutions and neutron irradiation on superconducting properties are discussed
[en] Materials science research can be both very demanding and extremely rewarding. In this Commentary, in my own research of new electronic and magnetic materials, I give numerous exemplars of the path followed to materials discovery. I also highlight the parallels between my research experiences with the pastime of running. I hope that my thoughts will help guide junior researchers along the often tortuous and exciting path to new materials and that I can teach them to be open minded and persistent about following new lines of discovery. “No-pain, no-gain” applies to many things in life, running and scientific research being just two examples, but I hope in the case of scientific research that I can convince you the gain normally outweighs the pain
[en] A large swath of quantum critical and strongly correlated electron systems can be associated with the phenomena of preserved entropy and fragile magnetism. In this overview we present our thoughts and plans for the discovery and development of lanthanide and transition metal based, strongly correlated systems that are revealed by suppressed, fragile magnetism, quantum criticality, or grow out of preserved entropy. We will present and discuss current examples such as YbBiPt, YbAgGe, YbFe2Zn20, PrAg2In, BaFe2As2, CaFe2As2, LaCrSb3 and LaCrGe3 as part of our motivation and to provide illustrative examples. (report on progress)
[en] We present an experimental study of the superconducting properties of NiBi3 as a function of pressure by means of resistivity and magnetization measurements and combine our results with density functional theory calculations of the band structure under pressure. We find a moderate suppression of the critical temperature from K to K by pressures up to 2 GPa. By taking into account the change of the band structure as a function of pressure, we argue that the decrease in is consistent with conventional, electron–phonon-mediated BCS-type superconductivity. (paper)
[en] In the spirit of searching for Gd-based, frustrated, rare earth magnets, we have found antiferomagnetism (AF) in GdPtPb, which crystallizes in the ZrNiAl-type structure that has a distorted kagome lattice of Gd triangles. Single crystals were grown and investigated using structural, magnetic, transport, and thermodynamic measurements. GdPtPb orders antiferromagnetically at 15.5 K, arguably with a planar, noncollinear structure. The high temperature magnetic susceptibility data reveal an “anti-frustration” behavior having a frustration parameter, |f| = |Θ|/T_N = 0.25, which can be explained by mean field theory within a two-sublattice model. Here, the study of the magnetic phase diagram down to T = 1.8K reveals a change of magnetic structure through a metamagnetic transition at around 20 kOe and the disappearance of the AF ordering near 140 kOe. In total, our work indicates that GdPtPb can serve as an example of a planar, noncollinear AF with a distorted kagome magnetic sublattice.
[en] The iron arsenic high-temperature superconductors exhibit particularly rich phase diagrams. In the AE(Fe1-xTx)2As2 family (known as '122', with AE being Ca, Sr or Ba and T being a transition metal), the simultaneous structural/magnetic phase transition that occurs at elevated temperature in the undoped material splits and is suppressed by carrier doping. A superconducting region appears as likely in the orthorhombic/antiferromagnetic (AFM) state as in the tetragonal/paramagnetic state. An important question then is what determines the critical doping at which superconductivity emerges, as the AFM order is fully suppressed only close to optimal doping. Here we report evidence from angle-resolved photoemission spectroscopy that marked changes in the Fermi surface coincide with the onset of superconductivity in electron-doped Ba(Fe1-xCox)2As2. The presence of the AFM order leads to a reconstruction of the electronic structure, most significantly the appearance of the petal-like hole pockets at the Fermi level. These hole pockets vanish - that is, undergo a Lifshitz transition - as the cobalt concentration is increased sufficiently to support superconductivity. Superconductivity and magnetism are competing states in this system: when petal-like hole pockets are present, superconductivity is fully suppressed, whereas in their absence the two states can coexist.
[en] We present data on the anisotropic magnetic properties, heat capacity and transport properties of CeGe2−x (x = 0.24) single crystals. The electronic coefficient of the heat capacity, γ ∼ 110 mJ mol−1 K−2, is enhanced; three magnetic transitions, with critical temperatures of ≈7, ≈5 and ≈4 K are observed in thermodynamic and transport measurements. The ground state has a small ferromagnetic component along the c-axis. Small applied field, below 10 kOe, is enough to bring the material to an apparent saturated paramagnetic state (with no further metamagnetic transitions up to 55 kOe) with a reduced, below 1.2μB, saturated moment. (paper)
[en] We report measurements of 57Fe Mössbauer spectra for RFe2Zn20 (R = Lu, Yb, Gd) from ∼4.5 K to room temperature. The obtained isomer shift values are very similar for all three compounds, their temperature dependence was analyzed within the Debye model and resulted in an estimate of the Debye temperatures of 450–500 K. The values of quadrupole splitting at room temperature change with the cubic lattice constant a in a linear fashion. For GdFe2Zn20, ferromagnetic order is seen as an appearance of a sextet in the spectra. The 57Fe site hyperfine field for was evaluated to be ∼2.4 T. (paper)
[en] We study the evolution of the Kondo effect in heavy fermion compounds, Yb(Fe_1_-_xCo_x)_2Zn_2_0 (0 ≲ x ≲ 1), by means of temperature-dependent electric resistivity and speci c heat. The ground state of YbFe_2Zn_2_0 can be well described by a Kondo model with degeneracy N = 8 and a T_K ~30 K. In the presence of a very similar total CEF splitting with YbFe_2Zn_2_0, the ground state of YbCo_2Zn_2_0 is close to a Kondo state with degeneracy N = 2 and a much lower TK ~ 2 K. Upon Co substitution, the coherence temperature of YbFe_2Zn_2_0 is suppressed, accompanied by an emerging Schottky-like feature in speci c heat associated with the thermal depopulation of CEF levels upon cooling. For 0.4 ≲ x ≲ 0.9, the ground state remains roughly the same which can be qualitatively understood by Kondo effect in the presence of CEF splitting. There is no clear indication of Kondo coherence observable in resistivity within this substitution range down to 500 mK. The coherence re-appears at around x≳ 0.9 and the coherence temperature increases with higher Co concentration levels.