J. M. Broto

Magnetotransport properties of the Kondo lattice YbPd2Si2, evidence for a new phase below 1.4 K

Abstract We study the heavy fermion properties of YbPd 2 Si 2 by resistivity, Hall effect and magnetoresistance. A new phase is found below 1.4 K.

Anomalous magnetocaloric effect in van vleck paramagnet HoVO4 near energy level crossing

The anomalous magnetocaloric effect in singlet rare-earth paramagnets near energy level crossing has been experimentally observed for the first time. The magnetization and differential magnetic susceptibility of Ho1 − xYxVO4 crystals (x = 0, 0.5) measured along the tetragonal axis in a pulsed magnetic field with various change rates near the crossover field, dH/dt, from 3 × 103 to 2.5 × 102 T/s are compared to the data in static magnetic fields down to 0.1 K. These data indicate the large negative magnetocaloric effect in the pulsed magnetic field, so that the crystal with the initial temperature T0 = 4.2 K is cooled much lower than 1 K. The experimental data are qualitatively described in the crystal field model with various interactions including hyperfine interactions and with the known interaction parameters.

Magnetic frustration in the spinel compounds GeNi2O4 and GeCo2O4

In the spinel compounds AB2O4, the B sites form a pyrochlore lattice. GeCo2O4 and GeNi2O4 have been investigated using high magnetic field magnetization as well as neutron diffraction measurements. Both compounds become antiferromagnetic at low temperature (around 23 and 12K, respectively) with the same propagation vector. The magnetization then presents two spin flop fields and one huge saturation field (above 50T). The Curie–Weiss temperature is positive for the Co spinel and negative for the Ni one. A model taking into account the first neighbor interaction J1 together with two different third neighbor interactions J2 and J3 is able to account for the common observed magnetic behavior. J1 is ferromagnetic while J2 and J3 are antiferromagnetic, in agreement with Goodenough–Kanamori–Anderson rules. These competing interactions are responsible for the frustration in these compounds.

Magnetic anomalies associated with the Tb3+ level crossing in YBa2Cu3Ox (x ≈ 6.0) in strong magnetic fields up to 50 T

Jumps of the magnetic moment of a Tb:YBa2Cu3Ox crystal (x ≈ 6.0) are observed in pulsed magnetic fields of up to 50 T for the field orientations along the [100] and [110] axes. The jumps are caused by the Tb3+ level crossing (crossover) in the layered perovskite structure. Based on the previously determined parameters of the crystalline electric field, the Zeeman effect, magnetization curves, and magnetic susceptibility curves are calculated for the Tb:YBa2Cu3Ox crystal in the tetragonal phase. The results of calculations provide an adequate description of the magnetic anomalies and the critical parameters of the crossover. The relatively large width of the jumps in magnetization curves can indicate the inhomogeneity of the second-order parameter of the crystalline electric field in the dilute crystals.

Jahn-Teller magnet TbVO4 in a strong magnetic field up to 50 T

Magnetic properties of the Jahn-Teller crystal TbVO4 are studied in pulse magnetic fields up to 50 T. The destruction of quadrupole ordering accompanied by an increase in crystal symmetry from orthorhombic to tetragonal has been revealed at Hc = 32 T. An adequate description based on the interaction parameters determined previously is proposed for magnetic anomalies and critical parameters of the induced phase transition. It is noted that the Jahn-Teller crystal TbVO4 may be of interest for investigations using synchrotron radiation in a pulsed magnetic field.

Energy dependent transport length scales in strongly diffusive carbon nanotubes

We report magneto-transport measurements in parallel magnetic field and μ-Raman spectroscopy on diffusive multiwall carbon nanotubes. The disorder effects on the characteristic transport lengths are probed by combining applied magnetic field and back-gate tuning of the Fermi level. Modulations of the differential conductance versus energy depict the modulation of the strength of the weak localization. Both the electronic mean free path and the phase coherence length are found to be energy dependent. The role of disorder in the density of states and in the characteristic transport lengths is discussed.