Strong Longitudinal Magnetic Fluctuations near Critical End Point in UCoAl: A ^59Co-NMR Study

TL;DR

This study uses ^59Co-NMR to investigate magnetic fluctuations in UCoAl near its critical end point, revealing strong longitudinal magnetic fluctuations that extend into the paramagnetic state.

Contribution

It provides the first detailed NMR evidence of enhanced longitudinal magnetic fluctuations near the critical end point in UCoAl.

Findings

Strong enhancement of longitudinal magnetic fluctuations near CEP

Diffusion of magnetic fluctuations into paramagnetic state

Distinct relaxation behaviors indicating fluctuation dynamics

Abstract

We report ^59Co-NMR measurements in UCoAl where a metamagnetism occurs due to enhancement of ferromagnetism by magnetic field. The metamagnetic transition from a paramagnetic (PM) state to a ferromagnetic state is a first order transition at low temperatures, but it changes to a crossover at high temperatures on crossing the critical end pint (CEP) at T_CEP ~ 12 K. The contrasting behavior between the relaxation rates 1/T_1 and 1/T_2 suggests that the longitudinal magnetic fluctuation of U moment is strongly enhanced especially near the CEP. A wide diffusion of the fluctuation from the CEP can be confirmed even in the PM state where the magnetic transition does not occur.