W. Knafo

Importance of in-plane anisotropy in the quasi-two-dimensional antiferromagnet BaNi2V2O8.

The phase diagram of the quasi-two-dimensional antiferromagnet BaNi(2)V(2)O(8) is studied by specific heat, thermal expansion, magnetostriction, and magnetization for magnetic fields applied perpendicular to c. At micro(o)H* approximately 1.5 T, a crossover to a high-field state, where T(N)(H) increases linearly, arises from a competition of intrinsic and field-induced in-plane anisotropies. The pressure dependences of T(N) and H* are interpreted using the picture of a pressure-induced in-plane anisotropy. Even at zero field and ambient pressure, in-plane anisotropy cannot be neglected, which implies deviations from pure Berezinskii-Kosterlitz-Thouless behavior.

The magnetic composition–temperature phase diagram of the kagome mixed system (CoxNi1−x)3V2O8

The magnetic composition–temperature (x–T) phase diagram of the mixed kagome system (CoxNi1−x)3V2O8 (CNVO) deduced from neutron powder diffraction and single-crystal heat capacity experiments is presented. CNVO changes its magnetic structure twice below 5.5 K as a function of the compositional parameter x. A sample with x = 0.98 has been found to be of a critical composition where both ferromagnetic and antiferromagnetic reflections of the Co3V2O8 (CVO) type magnetic structure have been observed in the diffraction pattern. Below this composition the ferromagnetic phase is completely suppressed and antiferromagnetic short-range order is present, which is modulated by a propagation vector k1 = (0,δ,0) with δ being temperature and composition dependent. Below 4.2 K δ has a constant value of 0.4 for 0.76<x<0.92. In the region 0.71<x<0.76 a change of the magnetic structure into the long-range ordered Ni3V2O8 (NVO) type with k2 = (δ,0,0), where δ is only dependent on x, takes place. Finally, for x<0.035 the positions of the magnetic reflections become temperature dependent again.

Resistivity of Mn1−xFexSi Single Crystals: Evidence for Quantum Critical Behavior

ohneysen Abstract Resistivity measurements have been made on Mn1−xFexSi single crystals between 2 and 300 K for x = 0, 0.05, 0.08, 0.12 and 0.15. Fe doping is found to depress the magnetic ordering temperature from 30 K for x = 0 to below 2 K for x = 0.15. Although Fe doping results in a large increase of the low-temperature residual resistivity, the temperature dependence of the resistivity above the magnetic transition remains practically unaffected by increasing Fe content. An analysis of the temperature derivative of the resistivity provides strong evidence for the existence of a non-Fermi-liquid ground state near x = 0.15 and thus for a quantum critical point tuned by Fe content.

Magnetic structure of the Kagomé mixed compound (Co0.5Ni0.5)3V2O8

MS38 P05 Magnetic structure of the Kagomé mixed compound (Co0.5Ni0.5)3V2O8 N. Qureshi, H. Fuess, H. Ehrenberg, B. Ouladdiaf, T. C. Hansen, Th. Wolf, C. Meingast, Q. Zhang, W. Knafo, H. v. Löhneysen Institute for Materials Science, University of Technology, Darmstadt, Germany. Institut Max von Laue-Paul Langevin, Grenoble, France. Leibniz Institute for Solid State and Materials Research, Dresden, Germany. Research Center Karlsruhe, Institute of Solid State Physics, Karlsruhe, Germany. Physics Institute, Karlsruhe University, Karlsruhe, Germany. E-mail: navidq@st.tu-darmstadt.de