Seminars

High magnetic field studies of the heavy fermion compounds URu<sub>1.92</sub>Rh<sub>0.08</sub>Si<sub>2</sub> and URu<sub>2-x</sub>Re<sub>x</sub>Si<sub>2</sub>

by Sonia Francoual, National High Magnetic Field Laboratory, Los Alamos National Laboratory, USA

Europe/Berlin
Bldg. 25b, Room 109

Bldg. 25b, Room 109

Description
URu2Si2 is a heavy fermion compound and itinerant electron metamagnet (IEM) the low-temperature and high magnetic field phase diagram of which is characterized by the formation of multiple ordered phases in the 30 to 42 T magnetic field range around a putative quantum critical point (QCP) located at 38 T. (§1) When 4 % of Ru atoms is substituted with Rh, a single field-induced robust phase II remains around a QCP shifted to 35 T. In order to address the coupling with the lattice of the order parameter in phase II, we have investigated the magnetostriction and thermal expansion properties in URu1.92Rh0.08Si2 using the parallel-plate capacitive dilatometry technique in DC fields up to 45 T below 30 K down to 1.5 K. We evidence important dilation effects in the underlying Fermi liquid outside phase II as observed in the 4f analog IEM compound CeRu2Si2 and also anisotropic and significant length changes at entrance into phase II pointing towards a longitudinal spin density-wave order parameter. (§2) Under rhenium doping, ferromagnetism (FM), Kondo lattice and Non Fermi liquid behaviors coexist in URu2-xRexSi2 at low temperatures. In order to address the consequences of the emergent ferromagnetism on the IEM and the field-induced ordering, we have measured transport and magnetization in pulsed magnetic fields up to 65 T in URu2-xRexSi2 x ≤ 50 %. We show that FM and KL behaviors coexist but compete for 0.15 ≤ x ≤ 0.35 as supported by recent neutron scattering measurements which AF/FM competition yields spin disorder and a detuning of the QCP. The ordering around the QCP is suppressed as soon as x = 5 %. Surprisingly, the metamagnetic transition goes to higher fields with x in a linear fashion up to x = 35 % and is observed deep inside the FM phase at x = 50 %.