3 research outputs found
Unconventional Strong Spin-Fluctuation Effects around the Critical Pressure of the Itinerant Ising-Type Ferromagnet URhAl
Resistivity measurements were performed for the itinerant Ising-type
ferromagnet URhAl at temperatures down to 40 mK under high pressure up to 7.5
GPa, using single crystals. We found that the critical pressure of the Curie
temperature exists at around ~ 5.2 GPa. Near , the -coefficient
of the Fermi-liquid resistivity term below is largely enhanced
with a maximum around 5.2-5.5 GPa. Above , the exponent of the resistivity
deviates from 2. At , it is close to , which is
expected by the theory of three-dimensional ferromagnetic spin fluctuations for
a 2nd-order quantum-critical point (QCP). However, disappears as a
1st-order phase transition, and the critical behavior of resistivity in URhAl
cannot be explained by the theory of a 2nd-order QCP. The 1st-order nature of
the phase transition is weak, and the critical behavior is still dominated by
the spin fluctuation at low temperature. With increasing pressure, the
non-Fermi-liquid behavior is observed in higher fields. Magnetic field studies
point out a ferromagnetic wing structure with a tri-critical point (TCP) at ~
4.8-4.9 GPa in URhAl. One open possibility is that the switch from the
ferromagnetic to the paramagnetic states does not occur simply but an
intermediate state arises below the TCP as suggested theoretically recently.
Quite generally, if a drastic Fermi-surface change occurs through , the
nature of the interaction itself may change and lead to the observed
unconventional behavior.Comment: 9 pages, 9 figure
Anomaly close to an electronic topological semimetal-insulator transition in elemental fcc-Yb under pressure
The Lifshitz-type semimetal-insulator transition, which is a transition of the
electronic topology, has been considered as the most fundamental metal-
insulator transition. Here, we present resistivity measurements under pressure
in the vicinity of the quantum critical point of fcc Yb. We apply a previously
suggested scaling for this type of transition and identify its universality
class. Moreover, we observe an anomaly in the screening coefficient A of the T
2 term in the resistivity at low temperatures in the metallic phase. We
suggest an interpretation of this phenomenon as an effect of doping by Ca
impurities unintentionally present in the Yb crystals. The observed behavior
may very well be applicable to any doped system in the vicinity of such a
transition