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

Single crystal growth and anisotropy of CeRuPO

We report on the single crystal growth of the ferromagnetic Kondo lattice system CeRuPO using a Sn flux method. Magnetic susceptibility and electrical resistivity measurements indicate strong anisotropy of this structurally layered compound. They evidence that the magnetic moments order ferromagnetically along the c-direction of the tetragonal unit cell, whereas the crystal electric field (CEF) anisotropy favors the ab-plane. Therefore, CeRuPO presents the unusual case within rare earth systems, where the anisotropy of the interionic exchange interaction overcomes the single ion anisotropy due to the CEF interaction.Comment: 13 pages, 7 figures, high quality figures: http://www.cpfs.mpg.de/~krellner

Single crystal growth and anisotropy of CeRuPO

We report on the single crystal growth of the ferromagnetic Kondo lattice system CeRuPO using a Sn flux method. Magnetic susceptibility and electrical resistivity measurements indicate strong anisotropy of this structurally layered compound. They evidence that the magnetic moments order ferromagnetically along the c-direction of the tetragonal unit cell, whereas the crystal electric field (CEF) anisotropy favors the ab-plane. Therefore, CeRuPO presents the unusual case within rare earth systems, where the anisotropy of the interionic exchange interaction overcomes the single ion anisotropy due to the CEF interaction.Comment: 13 pages, 7 figures, high quality figures: http://www.cpfs.mpg.de/~krellner

Magnetic field dependence of the antiferromagnetic phase transitions in Co-doped YbRh_2Si_2

We present first specific-heat data of the alloy Yb(Rh_(1-x)Co_x)_2Si_2 at intermediate Co-contents x=0.18, 0.27, and 0.68. The results already point to a complex magnetic phase diagram as a function of composition. Co-doping of YbRh_2Si_2 (T_N^{x=0}=72 mK) stabilizes the magnetic phase due to the volume decrease of the crystallographic unit cell. The magnetic phase transitions are clearly visible as pronounced anomalies in C^{4f}(T)/T and can be suppressed by applying a magnetic field. Going from x=0.18 to x=0.27 we observe a change from two mean-field (MF) like magnetic transitions at T_N^{0.18}=1.1 K and T_L^{0.18}=0.65 K to one sharp \lambda-type transition at T_N^{0.27}=1.3 K. Preliminary measurements under magnetic field do not confirm the field-induced first-order transition suggested in the literature. For x=0.68 we find two transitions at T_N^{0.68}=1.14 K and T_L^{0.68}=1.06 K.Comment: Accepted for the ICM proceedings 200

Development of the critical exponent at the antiferromagnetic phase transition of YbRh2Si2 under chemical pressure

We present specific-heat measurements in the vicinity of the antiferromagnetic phase transition on single crystals of the alloy Yb(Rh_{1-x}Co_x)2Si2 for x<= 0.38. This study was motivated by the violation of critical universality in the undoped YbRh2Si2 (Krellner et al., Phys. Rev. Lett. 102, 196402) where we have found a large critical exponent a=0.38. For Co-doped samples we observe a drastic change of the critical fluctuations resulting in a negative a, explainable within the universality classes of phase transitions. The development of a under chemical pressure gives strong indication that the violation of critical universality in YbRh2Si2 is due to the nearby quantum critical point.Comment: Accepted for the QCNP proceedings 200

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