Magnetic anisotropy of YbNi4P2

We report on transport and magnetic measurements between 1.8 and 400 K on single crystalline YbNi4P2, which was recently reported to be a heavy fermion system with a low lying ferromagnetic transition at T_C=0.17 K, based on data from polycrystals. The tetragonal crystal structure of YbNi4P2 presents quasi-one-dimensional Yb chains along the c direction. Here we show that at high temperatures, the magnetic anisotropy of YbNi4P2 is dominated by the crystal electrical field effect with an Ising-type behaviour, which gets more pronounced towards lower temperatures. The electrical resistivity also reflects the strong anisotropy of the crystal structure and favours transport along c, the direction of the Yb chains.Comment: SCES 2011 proceedings, in pres

Physical properties and crystal chemistry of Ce2Ga12Pt

Single crystals of the new ternary compound Ce2Ga12Pt were prepared by the self-flux technique. The crystal structure with the space group P4/nbm was established from single-crystal X-ray diffraction data and presents a derivative of the LaGa6Ni0.6 prototype. Magnetic susceptibility measurements show Curie-Weiss behaviour due to local Ce^3+ moments. At high temperatures, the magnetic anisotropy is dominated by the crystal-electric-field (CEF) effect with the easy axis along the crystallographic c direction. Ce2Ga12Pt undergoes two antiferromagnetic phase transitions at T_N,1 = 7.3K and T_N,2 = 5.5K and presents several metamagnetic transitions for the magnetic field along c. Specific-heat measurements prove the bulk nature of these magnetic transitions and reveal a doublet CEF ground state. The 4f contribution to the resistivity shows a broad maximum at T_max ~ 85K due to Kondo scattering off the CEF ground state and excited levels.Comment: 12 pages, accepted in J. Phys.: Condens. Matte

Magnetization study of the energy scales in YbRh2_{2}Si2_{2} under chemical pressure

We present a systematic study of the magnetization in YbRh$_{2}$Si$_{2}$ under slightly negative (6?% Ir substitution) and positive (7% Co substitution) chemical pressure. We show how the critical field $H_{0}$, associated with the high-field Lifshitz transitions, is shifted to lower (higher) values with Co (Ir) substitution. The critical field $H_{\mathrm{N}}$, which identifies the boundary line of the antiferromagnetic (AFM) phase $T_{\mathrm{N}}(H)$ increases with positive pressure and it approaches zero with 6% Ir substitution. On the other side, the crossover field $H^{*}$, associated with the energy scale $T^{*}(H)$ where a reconstruction of the Fermi surface has been observed, is not much influenced by the chemical substitution.}{Following the analysis proposed in Refs.\,\cite{Paschen2004,Gegenwart2007,Friedemann2009,Tokiwa2009a} we have fitted the quantity $\tilde{M}(H)=M+(dM/dH)H$ with a crossover function to indentify $H^{*}$. The $T^{*}(H)$ line follows an almost linear $H$-dependence at sufficiently high fields outside the AFM phase, but it deviates from linearity at $T \le T_{\mathrm{N}}(0)$ and in Yb(Rh$_{0.93}$Co$_{0.07}$)$_{2}$Si$_{2}$ it changes slope clearly inside the AFM phase. Moreover, the FWHM of the fit function depends linearly on temperature outside the phase, but remains constant inside, suggesting either that such an analysis is valid only for $T \ge T_{\mathrm{N}}(0)$ or that the Fermi surface changes continuously at $T = 0$ inside the AFM phase.}}Comment: 6 pages, 4 figure

Quantum criticality in Yb(Rh0.97Co0.03)2Si2 probed by low-temperature resistivity

Quantum criticality in Yb(Rh0.97Co0.03)2Si2 is investigated by means of resistivity and magnetoresistance. The partial substitution of Co leads to a stabilization of the magnetism as expected according to the application of chemical pressure for Yb systems. However, the signature of the Kondo-breakdown remains at the same position in the temperature-magnetic field phase diagram compared to stoichiometric YbRh2Si2. As a consequence, the Kondo-breakdown is situated within the antiferromagnetic phase. These results fit well within the global phase diagram under chemical pressure [1].Comment: 4 pages, 4 figures, submitted to ICM/SCES200

Interplay between Co-3d and Ce-4f magnetism in CeCoAsO

We have investigated the ground state properties of polycrystalline CeCoAsO by means of magnetization, specific heat and solid state NMR. Susceptibility and specific-heat measurements suggest a ferromagnetic order at about, $T_\mathrm{C}$=75 K. No further transitions are found down to 2 K. At 6.5 K a complex Schottky type of anomaly shows up in the specific heat results. The interplay between Ce-4f and Co-3d magnetism being responsible for that anomaly is discussed. Furthermore $^{75}$As NMR investigations have been performed to probe the magnetism on a microscopic scale. As-NMR spectra are analysed in terms of first and second order quadrupolar interaction. The anisotropic shift component $K_{\mathrm{ab}}$ and $K_{\mathrm{c}}$ could be derived from the $^{75}$As powder spectra. Towards lower temperature a strong shift anisotropy was found. Nonetheless $K_{\mathrm{iso}}$ tracks the bulk susceptibility down to $T=$50 K very well. Furthermore the presence of weak correlations among the Ce ions in the ferromagnetic state is discussed. The observed increase of $C/T$ towards lower temperatures supports this interpretation.Comment: 6 pages, 4 figures, Accepted in Physical Review