Direct observation of a magnetically ordered state inYbCu2Si2under high pressure

Abstract

The intermetallic compound YbCu 2 Si 2 is a well-known nonmagnetic ͑NM͒ Yb intermediate-valent compound with a Yb valence of 2.9 at ambient pressure and 300 K. In the present work we have investigated the effect of high pressure on the ground state properties of YbCu 2 Si 2 on both microscopic and macroscopic levels by using the 170 Yb Mössbauer effect, electrical resistance, and x-ray diffraction techniques, respectively. High-pressure x-ray diffraction data indicate that the lattice structure of YbCu 2 Si 2 is stable up to 22.2 GPa. The value of the bulk modulus ͓B 0 ϭ168(10) GPa Ϫ1 ͔ is found to be close to the value expected for trivalent RCu 2 Si 2 compounds. The pressure dependence of the electrical resistance reveals evidence for a pressureinduced magnetic order for pу8 GPa. From our Mössbauer data, we conclude a crossover from the NM to a magnetically ordered state of localized Yb moments for pу8 GPa and below 2 K. The pressure-induced change of the electric quadrupole splitting indicates that this transition is accompanied by a valence change towards the Yb 3ϩ state. ͓S0163-1829͑99͒01729-4͔

High-pressure X-ray diffraction study of UMn2Ge2

“…(1) is much smaller than the value of 215 GPa found for the compound, URu 2 Si 2 [10] (which has the same space group and comparable lattice parameter values) and of 168 GPa found for the compound, YbCu 2 Si2 [11]. This result shows that the present compound is much "softer" than URu 2 Si 2 , where Ru is a 4d transition element, and YbCu 2 Si 2 , where Yb is a rare-earth element.…”

Pressure dependence of the superconducting transition temperature inC6YbandC6CaSmith1, Kusmartseva2, Ko3 et al. 2006Phys. Rev. B437381View full textAdd to dashboardCite

“…There are many similarities between C 6 Ca and C 6 Yb; one significant difference is the Yb f-orbitals which at ambient pressure are predicted 5 to be well below the Fermi surface. At high pressures, in analogy with many Yb compounds which become more magnetic under pressure, 15 we may expect the Yb f-orbitals to move close to the Fermi surface, leading to the possibility of magnetism in C 6 Yb, which would be expected to have a significant effect on the superconductivity.…”

Pressure-induced residual resistivity anomaly in CeCu5Au

“…The magnitude of the ρ 0 peak in superconducting CeCu 2 Ge 2 at a pressure close to the T c (p) maximum, can be associated with charge fluctuations [7] or even a valence transition. For YbCu 2 Si 2 only a fraction of the Yb ions orders magnetically at p c [8] and the broad and shallow ρ 0 (p) maximum may correspond to full ordering at higher p. In the case of CeRu 2 Ge 2 the ρ 0 (p) variation at low p might be related to a change of the magnetic ordering vector between low and intermediate p the effect is rather small.…”