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 $P_c$ ~ 5.2 GPa. Near $P_c$, the $A$-coefficient of the $AT^{2}$ Fermi-liquid resistivity term below $T^*$ is largely enhanced with a maximum around 5.2-5.5 GPa. Above $P_c$, the exponent of the resistivity $\rho(T)$ deviates from 2. At $P_c$, it is close to $n = 5/3$, which is expected by the theory of three-dimensional ferromagnetic spin fluctuations for a 2nd-order quantum-critical point (QCP). However, $T_C(P)$ 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 $P_c$, the nature of the interaction itself may change and lead to the observed unconventional behavior.Comment: 9 pages, 9 figure

Magnetism and superconductivity of heavy fermion matter

The interplay of magnetism and unconventional superconductivity (d singlet wave or p triplet wave) in strongly correlated electronic system (SCES) is discussed with recent examples found in heavy fermion compounds. A short presentation is given on the formation of the heavy quasiparticle with the two sources of a local and intersite enhancement for the effective mass. Two cases of the coexistence or repulsion of antiferromagnetism and superconductivity are given with CeIn3 and CeCoIn5. A spectacular example is the emergence of superconductivity in relatively strong itinerant ferromagnets UGe2 and URhGe. The impact of heavy fermion matter among other SCES as organic conductor or high Tc oxide is briefly pointed out.Comment: 22pages, 15 figure

Uniaxial-Stress-Induced Ferromagnetism in the Itinerant Metamagnetic Compound UCoAl Probed by Magnetostriction Measurements

International audienceMagnetostriction measurements for the Ising-type itinerant metamagnetic compound UCoAl were performed under uniaxial stress for sigma parallel to c-axis using an in situ pressure-tuning device. A ferromagnetic transition was clearly observed at zero magnetic field at least above similar to 0.05 GPa. For a stress of 0.1 GPa, the FM transition is of 2nd order, since the anomaly of the thermal expansion coefficient does not show any hysteresis at the transition. No step like behavior was observed for the FM transition under uniaxial stress in the present study. From the precise stress dependence of T-C, a change of the power (n) law from 3/4 to 1/2 was also found at around 0.1 GPa for the expression of T-C(sigma) proportional to (sigma -sigma(c))(n), where the critical value is sigma(c) similar to 0.026 GPa

Spin-Triplet p -Wave Superconductivity Revealed under High Pressure in UBe 13

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Spin-Fluctuation Effects Near the Quantum Phase Transition of the Ising-Type Itinerant Ferromagnet URhAl

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Calorimetry Study of the Phase Diagrams of EuNi 2 Ge 2 and Eu 2 Ni 3 Ge 5 under Pressure

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Quantum Criticality of an Itinerant Ferromagnetic Compound URhAl Studied by Resistivity Measurements under High Pressure

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Calorimetric Study on EuCoGe 3 and EuRh 2 In 8 under Pressure

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