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Seminar: Petr Opletal

  • Petr Opletal: Development of magnetism in UCoAl with Ru doping and hydrostatic pressure
  • 9. 12. 2015, 14:50
  • lecture room F2, first floor Ke Karlovu 5
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Abstract:

Diverse quantum critical behavior of ferromagnets came into focus of both theoretical and experimental investigations in recent years [1]. One type of behavior is characterized by the itinerant electron metamagnetism at low temperatures. For such ferromagnets the Curie temperature (TC) is gradually suppressed with increasing applied hydrostatic pressure until the tricritical point (TCP) at finite temperature. At lower temperatures beyond TCP ferromagnetic  order can be induced through a first-order metamagnetic transition appears. Compounds like ZrZn2, or several uranium-based compounds like URhAl, UGe2 or UCoAl exhibit this type of phase diagram or large similarity.

UCoAl is a paramagnet down to low temperatures where, however, ferromagnetic order can be induced due to a metamagnetic transition at a critical field BC » 0.7 T. The first-order transition changes at TCEP = 10.2 K to the high-temperature crossover. The metamagnetic transition is suppressed with applied hydrostatic pressure until quantum criticality is reached at 2.9 GPa and 13 T [2]. UCoAl in ambient pressure is close to TCP which makes it a candidate for interesting research of this part of the phase diagram. For reaching the “ferromagnetic” part of the phase diagram uniaxial pressure applied along the c-axis or doping by specific transition-metal elements on Co positions appears effective.

Here we present our results of experiments with three single crystals of nominal compositions UCo0.99Ru0.01Al, UCo0.995Ru0.005Al and UCo0.9975Ru0.0025Al exhibiting behavior ranging from ground-state ferromagnetism to ground-state paramagnetism with metamagnetic transition. Data from magnetic, transport and dillatometry measurements in ambient and hydrostatic pressure are presented and relevant phase diagrams constructed.

1. M. Brando, D.B., F. M. Grosche, T. R. Kirkpatrick, Metallic Quantum Ferromagnets. http://arxiv.org/abs/1502.02898, 2015.

2. Kimura, N., et al., Quantum critical point and unusual phase diagram in the itinerant-electron metamagnet UCoAl. Physical Review B, 2015. 92(3): p. 035106.