Evidences for magnetic dimers and skyrmion lattice formation in Eu2_2Pd2_2Sn

Magnetic, thermal and transport properties of the non-centrosymmetric compound Eu$_2$Pd$_2$Sn are revisited after including new measurements. In its paramagnetic phase, the outstanding feature of this compound is the formation of Eu$^{2+}$ dimers that allows to understand the deviation of the magnetic susceptibility $\chi(T)$ from the C-W law below about 70\,K, the field dependent magnetization $M(B)$ variation below $\approx 80$\,K and the reduced entropy at the ordering temperature $S(T_N)= 0.64R\ln(8)$. A significant change of the exchange interactions occurs between $T\approx 70$\,K (where $\theta_P = 18$\,K) and $T_N = 13.3$\,K (where $\theta_P =-4.5$\,K). The strong electronic overlap, arising from the reduced Eu-Eu spacing compared with that of pure Eu$^{2+}$ is expected to power these quasiparticles formation, inducing a significant reformulation of the magnetic structure. A rich magnetic phase diagram is obtained from the analysis of the derivatives of the magnetic parameters: $\partial \chi/\partial T$ and $\partial M/\partial B$, and the field dependence of the specific heat. Two critical points are recognized and a tentative description of the magnetic structures is proposed. The possible formation of a skyrmion lattice, that arises from the presence of magnetically frustrated pockets in the phase diagram, is suggested by theoretical studies on hexagonal structures exhibiting similar interactions pattern.Comment: 13 pages, 11 figure

Searching for a quantum critical point in YbCu5-xAux

Structural, magnetic, transport and thermal properties of YbCu5-xAux alloys with Au concentration between the limit of structural stability of AuBe5 type at x = 0.4 up to x = 0.7 are reported. The outstanding features of this system are: i) the constant and record high values of Cm /T 7J/molK^2 below a characteristic temperature T*, ranging between 150 mK and 350 mK. ii) A power law thermal dependence dependence Cm/T(T>T*)=A/T^q, with q = 1.3 +/- 0.1, and iii) an arising incoherent electronic scattering observed in the resistivity at T < 1K for x < 0.6 despite the fact that Yb magnetic atoms are placed in a lattice. Magnetic frustration, originated in the tetrahedral distribution of Yb atoms, appears as the responsible of the exotic behavior of this system.Comment: 14 pages, 9 figure

Treatment with granulocyte colony-stimulating factor after allogeneic bone marrow transplantation for acute leukemia increases the risk of graft-versus-host disease and death

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POINT-CONTACT SPECTROSCOPY OF Ce 1-x REx Νi5 (RE = Pr , Nd)

We report on the study of the electron-quasiparticle interaction function in Ce 1-x RΕx Νi5 (RE = Pr, Nd) pseudobinary compounds for x = 0, 0.2, 0.5, 0.8, and 1 measured by means of point-contact spectroscopy. The measured point-contact spectra (d2V/dI2 -directly proportional to the electron-qnasiparticle interaction function) of the heterocontacts between Ce 1-x REx Ni5 and Cn in the ballistic regime are presented. PACS nnmbers: 73.40. Jn, 71.70.Ch, 71.70.Gm In this paper we present the results in Ce1-xRExΝi5 (RE = Pr, Nd) pseudobinary compounds obtained from point-contact (PC) spectroscopy in order to obtain information on the modification of the electron-quasiparticle interaction (EQI) function. In REΝi 5 compounds the Ni ions are not magnetic and the magnetic properties are determined by RE. CeΝi 5 is a Stoner enhanced paramagnet which is characterized by the influence of spin fluctuations on its properties In order to study the disappearance of the spin fluctuation effects in CeΝi5 [1] and the evolution of the CEF energy level scheme in these series we have measured polycrystalline samples of pseudobinary Ce 1 -x REx Hi5 series with x = 0.2, 0.5, and 0.8 by means of point-contact spectroscopy. The compounds Ce 1 -x Prx Ni 5 are all paramagnetic and Ce1-x Νdx Νi5 with x = 0.2, 0.5, and 0.8 are ferromagnetic with TC 2 K, 3.5 K, and 5.1 K, respectively The point-contact spectroscopy has proved to be a very useful experimental method for the direct study of the energy dependence of the interaction between conduction electrons and quasiparticle excitations in metal

Magneto-caloric effect in the pseudo-binary intermetallic YPrFe17 compound

We have synthesized the intermetallic YPrFe17 compound by arc-melting. X-ray and neutron powder diffraction show that the crystal structure is rhombohedral with View the MathML source space group (Th2Zn17-type). The investigated compound exhibits a broad isothermal magnetic entropy change {\Delta}SM(T) associated with the ferro-to-paramagnetic phase transition (TC \approx 290 K). The |{\Delta}SM| (\approx 2.3 J kg-1 K-1) and the relative cooling power (\approx 100 J kg-1) have been calculated for applied magnetic field changes up to 1.5 T. A single master curve for {\Delta}SM under different values of the magnetic field change can be obtained by a rescaling of the temperature axis. The results are compared and discussed in terms of the magneto-caloric effect in the isostructural R2Fe17 (R = Y, Pr and Nd) binary intermetallic alloys.Comment: Preprint, 5 pages (postprint), 4 figures, regular pape

YbPd2In : A promising candidate for strong entropy accumulation at very low temperature

We report on synthesis, crystal structure, magnetic, thermodynamic, and transport properties of the compound YbPd2In, crystallizing as a Heusler structure type. A trivalent state of the rare earth was determined by fitting the magnetic susceptibility with a Curie-Weiss law. This compound is characterized by showing very weak magnetic interactions and a negligible Kondo effect. A specific-heat jump was observed at T 48250mK, followed at higher temperature by a power-law decrease of CP(T)/T. The resulting large electronic entropy increase at very low temperature is rapidly shifted to higher temperature by the application of magnetic field. This magnetocaloric effect places YbPd2In as a very good candidate for adiabatic demagnetization cooling processes

The energy gap of intermediate-valent SmB6 studied by point-contact spectroscopy

We have investigated the intermediate valence narrow-gap semiconductor SmB6 at low temperatures using both conventional spear-anvil type point contacts as well as mechanically controllable break junctions. The zero-bias conductance varied between less than 0.01 mikrosiemens and up to 1 mS. The position of the spectral anomalies, which are related to the different activation energies and band gaps of SmB6, did not depend on the the contact size. Two different regimes of charge transport could be distinguished: Contacts with large zero - bias conductance are in the diffusive Maxwell regime. They had spectra with only small non-linearities. Contacts with small zero - bias conductance are in the tunnelling regime. They had larger anomalies, but still indicating a finite 45 % residual quasiparticle density of states at the Fermi level at low temperatures of T = 0.1 K. The density of states derived from the tunelling spectra can be decomposed into two energy-dependent parts with Eg = 21 meV and Ed = 4.5 meV wide gaps, respectively.Comment: 9 pages incl. 13 figure