Universality and Critical Behavior at the Critical-End-Point on Itinerant-Metamagnet UCoAl

Abstract

We performed nuclear-magnetic-resonance (NMR) measurements on itinerant-electron metamagnet UCoAl in order to investigate the critical behavior of the magnetism near a metamagnetic (MM) critical endpoint (CEP). We derived c-axis magnetization $M_c$ and its fluctuation $S_c$ from the measurements of Knight shift and nuclear spin-lattice relaxation rate $1/T_1$ as a function of the c-axis external field ($H_c$) and temperature ($T$). We developed contour plots of $M_c$ and $S_c$ on the $H_c$ - $T$ phase diagram, and observed the strong divergence of $S_c$ at the CEP. The critical exponents of $M_c$ and $S_c$ near the CEP are estimated, and found to be close to the universal properties of a three-dimensional (3-D) Ising model. We indicate that the critical phenomena at the itinerant-electron MM CEP in UCoAl have a common feature as a gas-liquid transition.

8 Pages, 14 figures

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• Metamagnetic Transition in UCoAl Probed by Thermoelectricity Measurements
• Critical behavior of magnetization in URhAl:Quasi-two-dimensional Ising system with long-range interactions
• Ferromagnetic Quantum Criticality Studied by Hall Effect Measurements in UCoAl
• Low-temperature Magnetic Fluctuations Investigated by ${}^{125}$Te-NMR on the Uranium-based Superconductor UTe${}_2$
• Anisotropic Uniaxial Pressure Response in UCoAl Studied by Nuclear Magnetic Resonance Measurement
• Ferromagnetic Critical Behavior in U(Co${}_{1-x}$Fe${}_x$)Al ($0\le x\le 0.02$) Studied by ${}^{59}$Co Nuclear Quadrupole Resonance Measurement
• Emergence of Elastic Softening Featuring Ultra-Slow Dynamics Around Magnetic Critical Endpoint in UCoAl
• Dramatic elastic response at the critical end point in UTe${}_2$
• Different universality classes of isostructural U$TX$ compounds ($T$ = Rh, Co, Co${}_{0.98}$Ru${}_{0.02}$; $X$ = Ga, Al)