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

TL;DR

This study investigates the critical magnetic behavior of UCoAl near its metamagnetic critical endpoint using NMR, revealing universal 3D Ising model characteristics and gas-liquid transition features.

Contribution

It provides the first detailed NMR analysis of critical phenomena at the metamagnetic critical endpoint in UCoAl, demonstrating universality and critical exponents.

Findings

Strong divergence of $S_c$ at the CEP

Critical exponents close to 3D Ising universality

Critical phenomena resemble a gas-liquid transition

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.